#sp0256aal2 — Public Fediverse posts

Who had “New OS for the Z80” On Their 2026 Bingo Card?

https://fed.brid.gy/r/https://hackaday.com/2026/04/12/who-had-new-os-for-the-z80-on-their-2026-bingo-card/

Who had “New OS for the Z80” On Their 2026 Bingo Card?

https://fed.brid.gy/r/https://hackaday.com/2026/04/12/who-had-new-os-for-the-z80-on-their-2026-bingo-card/

Minimalist Lo-Fi Minimalism – Part 2

Last year I programmed up an Arduino with my Pi Day MIDI Sequencer to play a short extract from Philip Glass’ Einstein on the Beach. You can read all about that here: Minimalist Lo-Fi Minimalism.

Having spent a fair bit of the time since then playing around with an Arduino and SP0256A-AL2 and finally getting it hooked up to MIDI, I parked an idle though that it might be interesting to get it “singing” part of Einstein on the Beach. This post comes back to that idea.

https://makertube.net/w/4upxhBNemynPiFKfdzzea2

Warning! I strongly recommend using old or second hand equipment for your experiments.  I am not responsible for any damage to expensive instruments!

These are the key Arduino tutorials for the main concepts used in this project:

• Minimalist Lo-Fi Minimalism
• SP0256A-AL2 Speech Synthesis
• Arduino and SP0256A-AL2 – Part 6
• Pi Day MIDI Sequencer

If you are new to Arduino, see the Getting Started pages.

Parts list

• 2x Arduino Uno
• Pi Day MIDI Sequencer
• Arduino SP0256A-AL2 Shield Design

The Circuit

I did wonder about combining both the Pi Day sequencer and SP0256A-AL2 shield into a single device, but then decided it would be simpler to treat them as two separate devices and use MIDI to pass control between them.

Consequently I’ve ended up as follows:

• Pi Sequencer -> MIDI TRS -> SL0256A-AL2 -> MIDI TRS -> synth

Where the Pi sequencer is running the code for Minimalist Lo-Fi Minimalism with a small update to send additional MIDI messages to be interpreted by the SL0256A-AL2. All other MIDI is passed through the SL0256A onto a MIDI synth as before.

The Code

Having decided on the basic architecture, the next decision was how to encode the information destined for the speech synthesizer. I need to be able to tell it a pitch and a number to be “sung”. I toyed with the following ideas:

• MIDI NoteOn with pitch, but using note velocity to encode the number to sing.
• MIDI Program Control to select the number, then MIDI pitch and velocity as normal.
• Use the MIDI channel for the number, and pitch and velocity as normal.

I opted for the last option, treating each number as a different instrument on a different MIDI channel. This is a bit wasteful but was a lot easier for testing than attempting to get a specific velocity or having to send MIDI PC messages to keep reselecting the “voice” before each note.

As described previously in Minimalist Lo-Fi Minimalism MIDI channels 1,2 and 3 are already used for the bass and two voice lines, so I’m using MIDI channels 4 through to 13 for the numbers one to ten.

The code for the Glass already has pitch and which number encoded into the data structures. To trigger the “singing” via the speech synthesizer I’m using the Soprano voice pitches, but an octave lower, so it is a relatively simple matter of adding in an additional MIDI send as follows:

    MIDI.sendNoteOn(sop[i], 64, MIDI_CHANNEL_SOP);              // Original code
    MIDI.sendNoteOn(sop[i]-12, 64, MIDI_CHANNEL_NUM-1+num[i]);  // New code
    lastsop = sop[i];                                           // Original code

It is using the “NUM” MIDI channel – 1 as I’m encoding the numbers 1 to 10 which are stored in the num[] array. As the speech synthesis is essentially running at a fixed duration for each utterance, I’m not even bothering with a Note Off message.

On the speech synth side, again essentially all of the code is the same as for the Arduino and SP0256A-AL2 – Part 6 MIDI code, but instead of singing “do, re, mi”, etc linked to pitch, I need to take the word from the MIDI channel. To do this, I’ve expanded the speak() function to include the number and call it as follows from the NoteOn callback:

  speak(channel-MIDI_CH2NUM, pitch);

This will result in a number from 1 to 10 and a MIDI pitch which can then be used to select the playback frequency as before and then say the allophones corresponding to the received number.

void speak (uint8_t num, uint8_t note) {
  midi2clock (note);
  switch(num){
    case 1:  // One
      spAllo(WW1);
      spAllo(AX1);
      spAllo(NN1);
      break;

    case 2:  // Two
      spAllo(TT2);
      spAllo(UW2);
      break;

  }
  spAllo(PA3);
}

The SP0256A-AL2 datasheet lists the allophones to use for the basic numbers.

I’ve used, in a few cases, slightly shortened versions of the numbers from one to ten. In particular I’ve removed the duplicate allophones for six and seven to make them a little shorter to playback.

The allophones for “One” includes the use of “SX” but I can find no other mention of that in the datasheet, so I’ve ignored it.

One final change was to tweak the timings of the original playback. I’ve had to slow it down a lot to give the SP0256A-AL2 time to say each number, and I’ve also introduced a small delay between sending the MIDI messages and updating the numbers on the display to allow them to sync up a little better.

If the MIDI went to the synth directly from the Pi Day sequencer then a delay would probably be required there too, but as it has to go through the SP0256A-AL2 and get sent back out using the “software THRU” of the Arduino MIDI library, it has a natural slight delay already and isn’t too noticeably out of sync.

Closing Thoughts

I always knew there would be a few limitations, not least of which due to the time it takes to play back the allophones, but in essence I believe this works. I’d rather it was a little more up tempo, but sometimes one just has to work with what is available.

I think it is certainly keeping within the spirit of attempting an extract of the original opera on 8-bit microcontrollers, so it’s not doing too badly.

Kevin

I've persuaded my SP0256A-AL2 to "sing" the Twelve Days of Christmas.

https://diyelectromusic.com/2025/12/23/sp0256a-al2-sings-the-twelve-days-of-christmas/

#SP0256AAL2 #ArduinoUno #MusicAdventCalendar #MyApologies #FiveGoldRings

SP0256A-AL2 Sings the Twelve Days of Christmas

Partly prompted by a programming challenge by Futzle on Mastodon, I thought it might be interesting to try to get my Arduino and SP0256A-AL2 to sing the Twelve Days of Christmas.

https://makertube.net/w/diBkzrhkh3tekAPBhGzrVj

Warning! I strongly recommend using old or second hand equipment for your experiments.  I am not responsible for any damage to expensive instruments!

These are the key Arduino tutorials for the main concepts used in this project:

• Arduino and SP0256A-AL2 – Part 5
• Arduino SP0256A-AL2 Shield Design
• SP0256A-AL2 Speech Synthesis

If you are new to Arduino, see the Getting Started pages.

Parts list

• Arduino Uno
• Arduino SP0256A-AL2 Shield

The Code

I wasn’t aiming for a clever code solution, as can be seen submitted to the programming competition already, but I was hoping to get the computer to do at least some of the work for me.

The first issue is getting a useful range for the song. My original MIDI SP0256 project managed around an octave and a half. Well it so happens that the 12 Days of Christmas is just over 1 octave, so if I can position that to the top end of the range, I should be ok.

This is the most compact notation of the tune that I know of. This is from the “Christmas Praise” Brass Band carol book, which seems to be one of the most common references for any band out caroling at this time of year.

Ignoring the introduction, I’m going to transpose this into concert Bb (i.e. up a minor third) which gives me a note range from F2 through to G3. This allows me to use a sensible range of the SP0256A without it getting too slow down at the bottom end of things.

The main text/lyric structure will be set up in a series of functions as follows:

intro() - "on the nth day of Christmas my true love gave to me"
nth() - "first", "second", etc.
one() - "a partridge in a pear tree"
two() - "two turtle doves"
...
twelve() - "twelve drummers drumming"

Some variations are required as follows:

• intro() – needs to be able to switch to “and a partridge” for all verses apart from verse 1.
• two(), three(), four() – have a different melody from verse 5 onwards.
• five() – ideally this should get slower and more drawn out with each repetition.
• one() – ideally this would slow down on the last time through.

In order to capture the variations and repeats for each verse, I’ve opted to use an increasing bitmask for each time through to trigger the various phrases. Bit 0 always indicates one() must be called. Bit 1 indicates two(), and so on. It starts with the value 1 but will keep adding another bit as the verses change, so will have the values 1, 3, 7, 15, 31, 63, etc. thus allowing me to build up the verses with one bit per verse.

one() takes bool parameters to indicate first time and last time through. two(), three(), four() take a bool parameter to indicate if it is a “post five gold rings” verse. Using the bitmask this is pretty easy as it just means any of the bits 0x0FF0 will be set for verses 5+.

Here is the main code loop.

uint16_t phrase=1;
for (int verse=1; verse<=12 ; verse++) {
  intro(verse);
  delay(200);
  if (phrase & 0x0800) twelve();
  if (phrase & 0x0400) eleven();
  if (phrase & 0x0200) ten();
  if (phrase & 0x0100) nine();
  if (phrase & 0x0080) eight();
  if (phrase & 0x0040) seven();
  if (phrase & 0x0020) six();
  if (phrase & 0x0010) five(verse);
  if (phrase & 0x0008) four(phrase & 0x0FF0);
  if (phrase & 0x0004) three(phrase & 0x0FF0);
  if (phrase & 0x0002) two(phrase & 0x0FF0);
  if (phrase & 0x0001) one(phrase == 1, verse == 12);
  phrase = (phrase<<1) + 1;
  delay(1000);
}

The timings were really quite tricky as I have several variables to work to:

• Each allophone takes a different time to be said.
• Each allophone also has a recommended delay time (this might be to account for the time to say them – I’m not sure).
• When I change the frequency, the time to say any specific allophone also changes, with lower frequencies significantly slower than higher ones.
• I naturally need to account for the musical rhythm changes too.

In principle I could probably work out the slowest interval and work back from there to get some accurate timings, but I just did a bit of trial and error on each phrase until it was close enough. The unevenness remaining was because I didn’t want to slow the whole thing down to the slowest phrases being “sung”. It is slow enough already!

Also, as it doesn’t look much, I’ve added an LED to light up at the start of an allophone and to go off whenever a pause is encountered.

Find it on GitHub here.

Closing Thoughts

I’m actually really pleased with this. It is a good balance of close enough to show the principle without me undertaking complex timing and endless fiddling.

I could probably get a bit cleverer with the code, but that wasn’t really the point for me. I’ve used an algorithm where it mattered to me, and was quite happy to spell out the allophones, frequencies, and timings by hand as I went.

Lastly, let me wish you the compliments of the season, to you and yours.

Kevin

#arduinoUno #sp0256aAl2

Arduino and SP0256A-AL2 – Part 6

Finally I’m doing something arguably slightly musical with my SP0256A-AL2! Playing it over MIDI.

• Part 1 – Basic introduction and getting started
• Part 2 – Arduino programmable clock
• Part 3 – Using a Raspberry Pi Pico as a programmable clock
• Part 4 – Using a HC4046 PLL as the clock
• Part 5 – Using an I2C SI5351 programmable clock
• Part 6 – Adding MIDI

https://makertube.net/w/wLRxeVHtMatYo7NGWCw54U

Warning! I strongly recommend using old or second hand equipment for your experiments.  I am not responsible for any damage to expensive instruments!

If you are new to microcontrollers, see the Getting Started pages.

The Circuit

This is using my Arduino SP0256A-AL2 Shield with an SI5351 programmable clock module, so this is essentially the circuit from Arduino and SP0256A-AL2 – Part 5 with the addition of a MIDI module.

I also used my Arduino MIDI Proto Shield but any MIDI RX circuit on the Arduino RX pin would work.

The same circuit can be made on solderless breadboard, but I’ve opted to use my PCBs for convenience as that is why I designed them in the first place.

The Code

I’m using all the main code from Arduino and SP0256A-AL2 – Part 5 but I’ve split the speaking into “start” and “stop” parts so I can drive them from MIDI NoteOn and NoteOff messages.

The main “speak” code now looks like the following:

void speak (uint8_t note) {
  if (note == 0) {
    spAllo(PA3);      // Speaking off
    return;
  }

  if ((note < MIDI_NOTE_START) || (note > MIDI_NOTE_END)) {
    return;
  }

  midi2clock (note);
  switch(note){
    case 36:  // Do
    case 37:
    case 48:
    case 49:
      spAllo(DD1);
      spAllo(OW1);
      break;

    case 38:  // Re
    case 39:
    case 50:
    case 51:
      spAllo(RR1);
      spAllo(EY1);
      break;

...

So when called with note==0 it will stop the speaking by sending PA3, but for any note between 36 and 56 it will set the frequency and then say the appropriate “Do, Re, Mi” word. I’ve used the same word for the natural and sharp equivalent. I’ve also allowed for two octaves. This is why there are four note values that result in the word “Do” being said: MIDI notes 36, 37 (C2 and C#2), 48, and 49 (C3 and C#3).

This can now be called from the code that handles MIDI Note On and Note Off messages.

Find it on GitHub here.

Closing Thoughts

It works, but it isn’t very responsive due to the time it takes to say each allophone.

I guess when I started thinking about doing this, I thought I’d get more of a frequency range from the device and wasn’t anticipating it being so “low” in the musical range either.

But it is quite fun to see it finally being driven by a music keyboard, even if it isn’t particularly practical!

I know there is emulation of an SP0256A-AL2 in the RC2040 (an emulation of the RC2014 on a Raspberry Pi Pico) so I might at some point look at seeing if I can just drop the hardware and doing it all in software at some point by adjusting sample and playback rates.

I suspect that will work a lot better, but it isn’t quite the same as driving the real thing 🙂

Kevin

#arduinoUno #midi #si5351 #sp0256aAl2

Arduino SP0256A-AL2 Shield PCB Build Guide

Here are the build notes for my Arduino SP0256A-AL2 Shield Design.

Warning! I strongly recommend using old or second hand equipment for your experiments.  I am not responsible for any damage to expensive instruments!

If you are new to electronics and microcontrollers, see the Getting Started pages.

Bill of Materials

• Arduino SP0256A-AL2 Shield PCB (GitHub link below)
• 1x SP0256A-AL2 (see notes here on sourcing: SP0256A-AL2 Speech Synthesis)
• Either 1x 3.579545 MHz oscillator (4-pin in 8-pin DIP footprint – see photos)
• Or 1x SI5351 breakout board (see photos)
• 2x 1KΩ resistors
• 3x 100nF ceramic capacitors
• 1x 1uF electrolytic capacitor
• 1x 3.5mm stereo TRS socket (see photos and PCB for footprint)
• 1x set of Arduino headers: 1x 10 pin; 2x 8 pin; 1x 6 pin
• Optional: 1x 28 pin wide DIP socket

Build Steps

Taking a typical “low to high” soldering approach, this is the suggested order of assembly:

• Resistors
• DIP socket (if used) and TRS socket.
• Disc capacitors.
• Electrolytic capacitor.
• 3-way jumper headers.
• Oscillator (if used)
• SI5351 pin headers (if used)
• Arduino headers

It should be decided up front if the board will use a fixed oscillator or a SI5351 programmable clock. Both could be installed, but there is a solder bridge that has to be used to determined which will be used. It isn’t possible to use both at the same time.

This shows the solder bridge configured to use the SI5351. This might be easiest to do prior to soldering other components on the board.

Here are some build photos.

Here is a photo with the oscillator installed, and one with the SI5351 instead.

Note: I didn’t solder the pin headers of the SI5351 to the PCB, but instead used the “fishing line trick” to push the board into the PCB without soldering. This means I have the option of reusing the board again for something else in the future.

By default the SP0256A-AL2 /RESET line is connected to the Arduino RESET pin. It is possible to break this link by cutting the solder bridge shown below and wiring the RESET pad to another Arduino GPIO pin.

Testing

I recommend performing the general tests described here: PCBs.

PCB Errata

There are no known issues with this PCB at this time.

Enhancements:

•  With hindsight it might have been useful to have a jumper option to select the clock mode rather than a solder bridge. But it seemed quite a fundamental choice at the time of designing the PCB that I thought it perhaps shouldn’t be quite so easy to change. Now I’m not so sure!

Find it on GitHub here.

Sample Applications

Here are some applications to get started with:

• Arduino and SP0256A-AL2 (and subsequent parts).

Closing Thoughts

Now it is a bit easier to experiment I can explore a few other musical possibilities.

But this has shown up a slight issue with the chips I have. The highest frequency that the chip can support without locking up seems to be somewhat device dependent.

I’ve seen nothing in the datasheet, application manual, or design guide that suggests it will function at all with anything other than a 3.12MHz oscillator, so I am running it quite a bit out of specification now.

Kevin

#arduinoUno #pcb #si5351 #sp0256aal2

Arduino SP0256A-AL2 Shield Design

Having spent quite a bit of time with an Arduino hooked up to an SP0256A-AL2 on a solderless breadboard, and now that I’ve got some ideas for how I want to sort out the clock, I thought it time to create a PCB to save the unreliable wiring getting in the way!

• Arduino SP0256A-AL2 Shield PCB Build Guide

Warning! I strongly recommend using old or second hand equipment for your experiments.  I am not responsible for any damage to expensive instruments!

If you are new to electronics and microcontrollers, see the Getting Started pages.

The Circuit

This is the basic circuit I’ve been using since Part 1 but I’ve added in an option to support the SI5351 from Part 5 instead of the oscillator, too. A solder jumper selects the clock source – there is no default setting.

There is also a (default closed) solder jumper on the RESET line in case there is a need to separate out the reset of the SP0256A-AL2 from the Arduino.

PCB Design

The PCB design is relatively straight forward. Using an Arduino Uno Shield template, all the components have fitted in quite well.

I had to create a custom symbol and footprint for both the SP0256A-AL2 itself and the SI5351 module I’m using.

The following GPIO pins are in use.

As already mentioned, the link between the two /RESET pins is via a solder jumper and pin header connection which can be broken if required.

I’ve added in additional breakout headers for all GPIO that isn’t connected to the SP0256A-AL2: D0-D1, D10-D13, A0-A3.

I’ve not included A4-A5 as these are connected to the SI5351 (if used).

Closing Thoughts

Hopefully this is a fairly straight forward design with no major surprises.

Kevin

#arduinoUno #pcb #si5351 #sp0256aal2

Driving the SP0256A-AL2 from an Arduino with a SI5351 I2C programmable clock.

This is starting to get useful now (finally) :)

https://diyelectromusic.com/2025/09/08/arduino-and-sp0256a-al2-part-5/

#Arduino #SP0256AAL2 #SI5351

Arduino and SP0256A-AL2 – Part 5

This looks at another of the options from Part 4 – the I2C programmable Si5351 clock source.

• Part 1 – Basic introduction and getting started
• Part 2 – Arduino programmable clock
• Part 3 – Using a Raspberry Pi Pico as a programmable clock
• Part 4 – Using a HC4046 PLL as the clock
• Part 5 – Using an I2C SI5351 programmable clock
• Part 6 – Adding MIDI

https://makertube.net/w/bX5QNRRkAomFJQo7qY17he

Warning! I strongly recommend using old or second hand equipment for your experiments.  I am not responsible for any damage to expensive instruments!

If you are new to microcontrollers, see the Getting Started pages.

I2C Si5351 Programmable Clock

From the datasheet of the Si5351:

“The Si5351 is an I2C configurable clock generator that is ideally suited for replacing crystals, crystal oscillators, VCXOs, phase-locked loops (PLLs), and fanout buffers in cost-sensitive applications. Based on a PLL/VCXO + high resolution MultiSynth fractional divider architecture, the Si5351 can generate any frequency up to 160 MHz on each of its outputs with 0 ppm error.”

The device itself requires a 3V to 3.6V supply, but typical breakouts seem to include a LDO regulator meaning it can be powered from 3V to 5V. Logic outputs are always 3V but the I2C lines will be the same as the power supply.

The Circuit

I’m using a breakout board like the one shown above. This has header pins for the three clock outputs, power and ground, and I2C. Although the si5351 device itself is a 3V3 device, most breakouts like this seem to include components to allow them to be powered by either 3V3 or 5V. I’m using 5V in my circuit.

I’m only using one of the clocks, so output 0 is fed into the OSC1 input of the SP0256A-AL2. Otherwise the rest of the SP0256A-AL2/Arduino circuit is the same as for part 1.

The Code

There are two libraries I’ve found for this:

• https://github.com/adafruit/Adafruit_Si5351_Library
• https://github.com/etherkit/Si5351Arduino

The Adafruit library is a fairly low-level interface to the device. The device basically has a multiplier which is used to set a PLL clock to somewhere between 600 and 900MHZ; and then a divisor to drop that back down to something useful.

But the reality of setting the parameters is actually quite complicated. There is a full discussion of how to do it, with some example Arduino code, here: https://rfzero.net/tutorials/si5351a/

It is not for the faint hearted!

Thankfully the second library mentioned above, by “EtherKit”, has a ‘set_freq()’ function that does it all for us. The code to use it is therefore fairly straight forward:

#include <si5351.h>
#include <Wire.h>

Si5351 si5351;

void clockSetup () {
  si5351.init(SI5351_CRYSTAL_LOAD_8PF, 0, 0);
  si5351.set_freq(300000000ULL, SI5351_CLK0);
  si5351.update_status();
}

void setClock (uint64_t freq) {
  si5351.set_freq(freq, SI5351_CLK0);
  si5351.update_status();
  delay(300);
}

The initialisation function requires three things:

• Which of 6, 8 or 10pF capacitors are used with the external oscillator.
• Frequency of the external oscillator. Passing in 0 uses the default, 25MHz.
• A parameter for frequency correction. I’m just using 0.

The set_freq() function takes a 64-bit value which gives a frequency in 0.01Hz units, so 3MHz is 3 followed by 8 zeros. This is an “unsigned long long” type, hence the “ULL” initialiser after the value in the code above. The other parameter states which clock to use – I’m just using clock 0.

It is possible to wire up a pot to an analog input and set the frequency using something like the following:

int alglast = 0;
void checkClock (void) {
  int algval = analogRead(ALG_IN);
  if  (algval != alglast) {
    uin64_t freq = 1000 + 5 * analogRead(ALG_IN); // in kHz
    setClock(freq*100000); // Convert to 0.01Hz units
  }
  alglast = algval;
}

This maps a pot reading onto frequency values between 1MHz and just over 6MHz in units of 5kHz.

Alternatively, it is possible to set pitches for individual allophones. I’ve found that loosely speaking, 3MHz seems to correspond to talking at the pitch of G#2 (MIDI note 44) which is an audio pitch frequency of round 98Hz. 6MHz is, as you might expect, G#3 (MIDI note 56 at 196Hz).

This means that the I can calculate the required clock frequency for a MIDI note M using the formula:

• Freq = 3MHz * 2 ^ (M – 44)/12

This function will set the clock based on the MIDI note number:

void midi2clock (int m) {
  if (m < 36 || m > 56) {
    return;
  }

  freq = 300000000 * pow (2.0, (((double)m-44.0)/12.0));
  setClock (freq);
}

Note how I’ve limited the range to between C2 (36) and G#3 (56), which means frequencies of 1.889MHz to 6MHz.

It would probably go a bit lower – down to 1MHz is probably practical from the point of view of the chip functioning, but not so useful from the point of view of how long it would take to say a single allophone. Anything higher will cause the SP0256A-AL2 to lock up in a funny state.

But that gives me a good octave and a fifth, which is quite a useful and practical range.

Warning: The top frequency seems to be device dependent for me. I have one that can support the full 1.5 octaves and one that locks up after just an octave, so some experimentation is required!

Find it on GitHub here.

Closing Thoughts

This is the most accurate and simplest to set up manner of providing a programmable clock I’ve found so far. The device itself is actually quite complex to use, but all that complexity has been hidden away in the Si5351 library published by EtherKit.

The device sometimes seemed to get stuck in a weird state where is wasn’t recognised on the I2C bus. A power cycle or reset, or some combination of both, was usually required to get it going again. I don’t know if that was dodgy cables somewhere, but when it got stuck, curiously my nearby FM radio receiver lost its signal… Hmm.

The downside of using the Arduino for both clock and speech control is that it isn’t possible to adjust the clock whilst the speech is happening. That would need some kind of parallel execution to manage that – either adding in another microcontroller, or maybe moving to a dual-core microcontroller.

But as you can hear from the end of the video, this could still be pretty useful and I wish I’d had it for my Electric Lo-Fi Orchestra Concerto for a Rainy Day.

Kevin

#arduinoUno #electricLofiOrchestra #include #si5351 #sp0256aAl2

Arduino and SP0256A-AL2 – Part 4

Having now tried both an Arduino and Raspberry Pi Pico as programmable clocks for the SP0256A-AL2, this post starts to look at some alternative solutions, starting with a HC4046 phase-locked loop, voltage-controlled oscillator clock.

• Part 1 – Basic introduction and getting started
• Part 2 – Arduino programmable clock
• Part 3 – Using a Raspberry Pi Pico as a programmable clock
• Part 4 – Using a HC4046 PLL as the clock
• Part 5 – Using an I2C SI5351 programmable clock
• Part 6 – Adding MIDI

https://makertube.net/w/8eRTaCvqb3bsmZEJFy94E3

Warning! I strongly recommend using old or second hand equipment for your experiments.  I am not responsible for any damage to expensive instruments!

If you are new to microcontrollers, see the Getting Started pages.

Some Ideas

Whilst trawling around the Internet (and remembering a comment from my earlier posts), I found two existing projects where changing the frequency was used as a way to add pitch to the SP0256A-AL2:

• The previously mentioned MIDI Narrator: https://rarewaves.net/products/midi-narrator/
• A great blog post on SP0256A-AL2 pitch control: https://www.polaxis.be/2011/11/sp0256-al2-pitch-control/

Both use a VCO approach. The latter using a LTC6903 programmable oscillator; and the former using a CD4046 PLL device.

The LTC6903 looks like it would be a lot more complicated for me to use (especially being SMT), but I have some DIP 4046 devices already in the parts drawer so that is definitely an option for me.

I’ve also found (and now ordered) some breakout boards based on the SI5351 based programmable clock module. They all seem to follow Adafruit’s lead: https://learn.adafruit.com/adafruit-si5351-clock-generator-breakout/overview

One last thought – use a 555. No really! There are some versions that can go up o 3, 4 or even 5MHz apparently, see: https://en.wikipedia.org/wiki/555_timer_IC#Derivatives Of course having that in any way programmable might be a challenge, but it isn’t out of the question.

4046 VCO/PLL

A voltage-controlled oscillator is just what it sounds like. An oscillator whose frequency is related to the level of a control voltage on its input.

Here is a pinout and functional view of the 4046 from the TI 74HC4046/74HCT4046 datasheet. This provides several phase comparators and a voltage-controlled oscillator to create a phased-locked loop controller.

A key statement is the following:

“The VCO requires one external capacitor C1 (between C1A and C1B) and one external resistor R1 (between R1 and GND) or two external resistors R1 and R2 (between R1 and GND, and R2 and GND). Resistor R1 and capacitor C1 determine the frequency range of the VCO. Resistor R2 enables the VCO to have a frequency offset if required.”

The “application information” section describes the “with offset” operation:

There are a lot of graphs of characteristics in the datasheet for the various combinations of R1, R2 and C1 – these are the “figure 27-32” mentioned above. Actually, to cover all options, there are figures 10 through to 43, but most of those cover other situations.

The criteria for selecting R1, R2 and C are:

• R1 Between 3kΩ and 300kΩ
• R2 Between 3kΩ and 300kΩ
• R1 + R2 Parallel Value > 2.7kΩ
• C1 Greater Than 40pF

For the MIDI Narrator, the values being used are as follows:

• R1 = 1.5K to 2.5K (adjustable)
• R2 = 12K
• C1 = 1nF

Which I believe puts it in the following areas of the performance curves, although they aren’t strictly within the state required ranges…:

So without detailed calculations and measurements, I think this puts the (centre) offset frequency at a low-number of MHz (extrapolating for 12K at 5V) and the Max/Min ratio (R2/R1) at something around 4 to 8.

I believe, from looking at the other charts, that a higher R1 or C value gives a lower frequency. There are graphs for the following with the stated approx frequency ranges at 4.5V:

• 1M5, 100nF: 0 < Freq <100Hz
• 150K, 100nF: 0 < Freq < 1kHz
• 5K6, 100nF: 0 < Freq < 20kHz
• 150K, 50pF: 0 < Freq < 1.5MHz

One last thing to note from figure 32 – it states that a Vin of 0.95 VCC will generate the maximum frequency and 0V for the minimum.

It turns out I have some CD4046 in my parts box, not a HC or HCT 4046. On initial inspection, there doesn’t seem to be a lot of difference that would significantly affects my messing around. Some of the pins (that I’m not using) have different functions:

But as I’m not using those pins, that probably won’t matter. But then on closer inspection, I can see a key difference that definitely will affect my messing about – the operating frequency ranges:

• HC/HCT4096: Up to 18MHz at VCC=5V.
• 4096: Up to 1.4MHz at VDD=10V.

And digging into the detailed spec for the CD4046, when running at 5V the maximum is down to just 0.8MHz typical.

So I could use them to test out some general principles but need a HC/HCT version to really achieve what I’d like to do.

At this point my understanding was starting to struggle, and those graphs weren’t helping much. So I just went ahead and built the version of the circuit from the Rarewaves MIDI Narrator. I really wasn’t having much luck with it as is however, so started fiddling about with different components and an oscilloscope to see if I could make any sense from it.

There is a good article about the basics of a 4046 based VCO-driven PLL oscillator output here: https://hackaday.com/2015/08/07/logic-noise-4046-voltage-controlled-oscillator-part-one/

I was finding that the output wasn’t a particularly clean square wave, and at higher frequencies was pretty much triangular. At this stage I don’t know how much of that is my measuring equipment. I have a scope probe with a 10pF capacitance apparently, so a 10K resistor and 10pF capacitor do create a low-pass filter that significantly rounds off the signal.

But more significantly, the peak to peak voltage was greatly reduced to around 1.5Vpp with a significant BC bias. That wasn’t much use as a clock signal for me – from Part 3 I know the SP0256A-AL2 requires <0.6V for a LOW and >2.5V for a HIGH. Basically scope or on scope the output was pretty unreliable for me.

I’d included the 10K resistor between the 4046 and SPA256A-AL2 as per the circuit for the MIDI narrator. But without that resistor, the clock is much cleaner and has much more useful levels, so I removed it. Later experiments show that a 1K resistor seems to work fine too.

I also found that the suggested 1nF capacitor wasn’t giving me a particularly useful range. In the end, 4.7nF seemed to work well for me. Eventually after testing a range of different resistor values, I went back to 12K and 1.5K + 1K pot from the original circuit. This gives me:

• The frequency range set by a combination of 4.7nF and 12K.
• A frequency offset of between 1K and 2.5K is configurable.

I believe this will pull the frequency offset down slightly from the previous values to something between 100kHz and 600kHz, according to the charts, but it gives me a very useful range between around 1MHz and 5MHz once tuned slightly with the trimpot.

When going through the LM358 the usable voltage range for the VCO seems to be between ~2V and 3V for the 1MHz to 5MHz range. 0V is currently giving me 120kHz, tweaking of the offset resistor (R2 = 12K) helps here – 3K3 makes that around 500kHz, making the useful input voltage now around 1.5V to 3V. The issue is that reducing R2 starts to get to the point where the condition that R1||R2 > 2K7 no longer holds true. But either seems fine for some experimenting for now.

My final circuit used for now is as follows:

The CLK output was plugged directly into the SP0256A-AL2 OSC 1 input, with OSC 2 connected to GND.

The control voltage pot goes through a LM358 which might not be strictly necessary in this case, but helps to at least stabilise the input voltage to the VCO. It might also be useful when I switch to programmatically driving the control voltage from a microcontroller.

The usable clock frequency range is adjusted using the trimpot. Eventually, as mentioned, I settled on a range of around 1MHz to 5MHz. It will go lower, but that isn’t so useful for driving the SP0256A-AL2.

Arduino PWM Voltage Control

To get the Arduino to set the control voltage, requires generating a PWM signal which can be pretty simply done with analogWrite().

The default PWM frequency is around 400kHz without messing about directly with Arduino timers. This will need filtering though, but a simple low-pass filter should easily work here, especially as the frequency won’t be changing very often.

I just went back to the MIDI narrator circuit and could see that a 100K/220nF filter was used. Putting these into a low-pass filter calculator gives a cut-off frequency of just under 8Hz. This generates a pretty smooth output.

There is a balance between the frequency range and offset chosen for the 4046 by the selection of R1, R2 and C, and the voltage range sent out of the Arduino. After a fair bit of messing around, I settled on the following:

• R1 = 3K3
• R2 = 10K
• C = 560pF

Then used analogWrite() with values between 60 and 200 to generate voltages and frequencies as follows:

• analogWrite() value range: 60 to 200
• PWM smoothed voltage range: 1.3V to 3.6V
• LM258 output voltage range: 1.3V to 3.3V
• Clock frequency range: 2.2MHz to 5MHz

Setting up the clock via PWM voltage control is done as follows:

#define SP0_CLOCK 10 // D10
void clockSetup () {
  pinMode(SP0_CLOCK, OUTPUT);
  analogWrite(SP0_CLOCK, 128);  // Approx 2.5V output
}

void setClock (int clock) {
  analogWrite(SP0_CLOCK, clock);
}

Closing Thoughts

This seems to work really well. The control using a pot isn’t particularly reliable, but that is quite different if generating a control voltage from a microcontroller.

I still need to do some calibrations to work out what voltages create which frequencies and then what pitch of voice reproduction that seems to produce, but that can come later. For now it is enough to know it appears to work albeit in still quite a hand-wavy kind of way.

As an aside, whilst trawling around the Internet for this one I stumbled across the CTS256A-AL2 device. This is a microcontroller (I think it is 8051 based, based on a PIC7041) that performs text to allophone conversion for pairing with a SP0256A-AL2 for a complete text to speech system.

There are some details, and an interesting DIY board, here: https://www.smbaker.com/cts256a-al2-text-to-speech-board and an older project here: https://8051bits.com/misc-projects/speech%20-%20music%20synthesizers/speech-mus-syn.html

Unfortunately these seem very hard to come by these days, but there is some interesting emulation code here: https://github.com/GmEsoft/SP0256_CTS256A-AL2

And a pretty thorough discussion about the device and its running code here: https://www.retrobrewcomputers.org/forum/index.php?t=msg&th=816&goto=10847

Kevin

#74HC4046 #arduinoUno #define #pll #sp0256aAl2

Arduino and SP0256A-AL2 – Part 3

Following on from using an Arduino as a variable clock in Arduino and SP0256A-AL2 – Part 2, I have some ideas for a few options, but this post looks in detail at using a Raspberry Pi Pico as the clock source.

Spoilers: it kind of works, but isn’t quite the answer I need yet…

• Part 1 – Basic introduction and getting started
• Part 2 – Arduino programmable clock
• Part 3 – Using a Raspberry Pi Pico as a programmable clock
• Part 4 – Using a HC4046 PLL as the clock
• Part 5 – Using an I2C SI5351 programmable clock
• Part 6 – Adding MIDI

https://makertube.net/w/bxBYCqHrZvQLwLuwYa5Z9r

Warning! I strongly recommend using old or second hand equipment for your experiments.  I am not responsible for any damage to expensive instruments!

If you are new to microcontrollers, see the Getting Started pages.

Using a RPi Pico

The RP2040 can be overclocked quite a bit, so generating a variable square wave up in the few MHz range should presumably be relatively straight forward. Using the built-in PIO state machines for a square wave is fairly simple and it can be done from Circuitpython or Micropython too.

This is a complete square wave generator for GP2 that steps down from 4MHz to 2MHz in steps of 100kHz. It can optionally overclock the RPi to 250 MHz too if required.

import time
import microcontroller
import board
import rp2pio
import adafruit_pioasm

square = adafruit_pioasm.assemble ("""
.program square
    set pins, 1
    set pins, 0
""")

RP2040Freq = 125_000_000
#RP2040Freq = 250_000_000

print ("RP2040 Frequency = ", microcontroller.cpu.frequency)
microcontroller.cpu.frequency = RP2040Freq
time.sleep(1)
print ("New RP2040 Frequency = ", microcontroller.cpu.frequency)

while True:
    for freq in range (4000000, 2000000, -100000):
        print("\nReqd frequency = ", freq*2)
        print("Sq frequency = ", freq)

        sm = rp2pio.StateMachine(
            square,
            frequency=freq*2,
            first_set_pin=board.GP2,
        )
        print("Actual freq = {:d}".format(sm.frequency))
        print("Actual sq freq = {:d}".format(int(sm.frequency/2)))

        time.sleep(5)
        sm.deinit()

The PIO program itself has two instruction steps, so takes two cycles to complete, so the running frequency has to be twice the desired frequency of the square wave. It automatically keeps looping, so no additional instructions are required there.

The state machine will run at the system speed with a 16.8 fixed point fractional clock divider. Full details can be found in section 3.5.5 “Clock Dividers” in the RP2040 datasheet.

For certain values there might be some jitter:

If the system clock is faster though, the amount of jitter will be less I suspect, so it is advantageous to overclock the Pico for more accurate frequencies.

The problem with this approach is that whilst I get a nice accurate clock source with quite a good resolution across its range, every time the state machine is recreated to change the frequency, there is a “blip” in the audio from the SP0256A-AL2 whilst its clock temporarily disappears!

An alternative approach is to use a fixed state machine frequency but include a counter in the PIO program to allow for a configurable number of steps per scan of the PIO without having to stop and restart the clock.

The problem with this is that I am limited to a unit of the instruction time for the PIO state machine which gives a fixed overhead, in terms of the instructions required for a minimal loop, and a flexible overhead, in terms of the counter I can pass in.

The upshot of this is that I’m tied to a certain resolution of frequency change.

I have the following PIO code:

.program blink
.side_set 1
.wrap_target
    pull noblock
    mov x, osr
    mov y, x
    set pins, 1
lp1:
    jmp y-- lp1
    nop
    nop
    mov y, x
    set pins, 0
lp2:
    jmp y-- lp2
.wrap

The “pull” will update the output shift register (OSR) either with any new value written to the state machine or the last value of the X register. This value gets copied to Y to use as a counter. This happens twice, once for when the pin is set at 1 and once for when the pin is set at 0.

There are two nops whilst the pin is set at 1 to balance for the original pull and mov instructions at the end of the pin set to 0 cycle.

As the Y counter value is used twice, the flexible overhead of the timing is essentially proportional to count * 2. It counts for the pin being HIGH and then for the pin being LOW.

The fixed overhead is the cost of the original pull, two moves, the pin sets, and a single jmp per pin state – so by using the two nops to ensure the HIGH and LOW times are the same, that is 10 instruction cycles.

I was hoping to use the “side” instruction to eliminate the two set instructions, but so far I’ve not managed to get that to work. I still don’t understand PIO…

So for now the timing of the PIO routine is = 10 + 2 * count and the unit is the time for a single instruction, which is 1 / frequency of the PIO execution, up to a maximum frequency of the Pico’s system clock frequency.

Using an overclocked Pico at 250MHz, the frequency range would start at the following:

• Execution freq = Pico Sys Clock / (10 + 2 * count)
• So when count = 0; execution freq = 250MHZ / 10 = 25 MHz

That is far too fast for the SP0256A-AL5. In fact, I’ve found that anything over around 5MHz causes the chip problems.

For this reason, I’m using a minimum count of 20:

• Max execution freq = 250MHz / (10 + 2 * 20) = 5 MHz

Plotting execution frequency per “count” value (starting from 20) gives the following:

We can see the limits of the resolution at the top-end, and in fact, the first few equivalent frequencies in that range are as follows:

That is giving me something like a 150-200kHz jump each time, which isn’t great, but is probably the best I can do. I would be larger if I wasn’t overclocking the Pico. It does get smaller as the count increases, but it is only really worth going down to a count value of around 120, which is around 1MHz for the resulting clock. Anything lower than that and the SP0256A-AL2 isn’t particularly useful.

Here is the full Circuitpython code which attaches a pot to GP26 to control the frequency in the range of around 900kHz up to 5MHz. Note the scaling of the pot value (0 to 65535) by 600 prior to its use to add to the count.

import array
import time
import board
import rp2pio
import microcontroller
import adafruit_pioasm

from analogio import AnalogIn
algin = AnalogIn(board.GP26) # ADC0

blink = adafruit_pioasm.assemble(
    """
.program blink
.side_set 1
.wrap_target
    pull noblock
    mov x, osr
    mov y, x
    set pins, 1
lp1:
    jmp y-- lp1
    nop
    nop
    mov y, x
    set pins, 0
lp2:
    jmp y-- lp2
.wrap

"""
)

RP2040Freq = 250_000_000

microcontroller.cpu.frequency = RP2040Freq
time.sleep(1)

oldalgval = 0

sm = rp2pio.StateMachine(
            blink,
            frequency=RP2040Freq,
            first_set_pin=board.GP2
        )
sm.write(bytes(16))

while True:
    algval = algin.value
    if (algval != oldalgval):
        oldalgval = algval
        count = 20 + int(algval / 600)
        freq = int (RP2040Freq / (10 + count*2))
        data = array.array("I", [count])
        sm.write(data)

    time.sleep(0.2)

One problem will be the 3V3 operating levels of the Pico. The SP0256A-AL2 datasheet states the following:

So whilst a “high logic” value for the oscillator has a minimum level of 2.5V, it also states that a minimum of 3.9V is required if driven from an external source.

If required, something like a 74HCT14, powered by 5V, can be used to level shift the 3V3 output of the Pico to a 5V signal for use with the SP0256A-AL2.

But in practice, I was finding the Pico worked fine as is. It is important to ensure both the Pico, Arduino and SP0256A-AL2 all have their grounds connected.

A this point I’m just using the Pico as a programmable clock, but if I was to go this route, then it would make sense to have the Pico drive the SP0256A-AL2 too and forgo the Arduino.

Closing Thoughts

So I have two choices if I want to use a Raspberry Pi Pico:

• Go for smooth changes of frequency, but with less resolution, especially at the higher frequencies.
• Go for more accurate resolution across the range but accept there will be blips when the clock changes which will be heard in the audio.

Neither is a perfect solution, but it shows the principles are valid. Also, using two microcontrollers is a bit over the top, so if I was to move to using a Pico, I’d probably want to find a way to drive the SP0256A from the Pico directly too and skip using an Arduino.

One benefit of that would be that I can time the frequency changes to coincide with silence in the speaking should I wish to, avoiding the possibility of major audio blips.

But I also have a few other options to try, which I’ll come back to in a future post.

Kevin

#arduinoUno #pio #raspberryPiPico #sp0256aAl2

Arduino and SP0256A-AL2 – Part 2

After getting the Arduino and SP0256A-AL2 working I wondered if I could repeat the trick from the Arduino and AY-3-8910 and have the Arduino generate the required clock signal for the SP0256A-AL2. This post starts to look at that question.

• Part 1 – Basic introduction and getting started
• Part 2 – Arduino programmable clock
• Part 3 – Using a Raspberry Pi Pico as a programmable clock
• Part 4 – Using a HC4046 PLL as the clock
• Part 5 – Using an I2C SI5351 programmable clock
• Part 6 – Adding MIDI

https://makertube.net/w/paGX4eiCAHgLU9mK2x3uyq

Warning! I strongly recommend using old or second hand equipment for your experiments.  I am not responsible for any damage to expensive instruments!

If you are new to Arduino, see the Getting Started pages.

Parts list

• Arduino Uno
• SP0256A-AL2 speech synthesizer chip
• 2x 1KΩ resistors
• 2x 100nF capacitors
• 1x 1uF capacitor
• 1x 3.5mm jack socket
• Breadboard and jumper wires

The Circuit

This is basically the same setup as the previous post, but instead of the 3.579345 MHz oscillator, the clock input of the SP0256A-AL2 is connected to the Arduino D10 pin.

D10 is internally connected to OC1B, or the “B” compare match output of Timer 1 of the ATMega328P.

The Code

To get a clock signal of any kind on one of the output pins requires use of the ATMega328’s timers – in this case Timer 1. This is a 16-bit timer.

To generate an automatic (i.e. with no code driving it once it is set up) square wave signal on the Arduino’s output pin requires the timer to be connected to an output pin to generate a 50% duty cycle PWM signal.

The PWM peripherals can be configured to toggle an output pin when the timer expires, but that therefore requires the PWM to be running at least twice as fast as the required frequency.

From the SP0256A-AL2 datasheet, it has this to say about clocks.

There isn’t a lot to go on here – basically it assumes a 3.12MHz clock with a 48-52% duty cycle for the square wave.

A typical application circuit would be the following (again from the datasheet):

And the final word on oscillators is in the pin descriptions:

The options for creating a 3.12 MHz clock with an Arduino PWM output are pretty limited, due to the following:

• The faster clock for PWM is related to the system IO clock speed of 16MHz, when running with no “prescalar” to drop it down in frequency.
• When running at 16MHz, lower frequencies are obtained by using the “compare match” approach. The timer will reset and the output pin will toggle when a counter match occurs. The counter will count in integer units of the core 16MHz frequency.
• As the output pin will toggle on compare match, the timer must run at twice the frequency of the required clock signal. This allows one period for a HIGH output and one period for a LOW output to generate the required square wave output.

The PWM square wave frequency is given by the following formula (as per the ATMega328P datasheet for Timer 1,3,4):

• Freq = FreqClk / (2 * prescalar * (OCR1B + 1))

Given the above, with a FreqClk of 16MHz, the following are the only real options for a PWM-driven square wave as a clock for this application:

So there isn’t a lot of choice, and nothing particularly close to the required 3.12 MHz, although 2.7 MHz is the closest and would probably do if required.

To configure the above requires the following code:

#define SP0_CLOCK 10 // D10
void clockSetup () {
  pinMode(SP0_CLOCK, OUTPUT);
  digitalWrite(SP0_CLOCK, LOW);

  TCCR1A = (1 << COM1B0);
  TCCR1B = (1 << WGM12) | (1 << CS10);
  TCCR1C = 0;
  TIMSK1 = 0;
  OCR1AH = 0;
  OCR1AL = 1;
}

This configures Timer 1 in Clear-Timer-on-Compare (CTC) mode with no prescalar, toggling OC1B on compare match with the value in OCR1A.

Note: even though there are two pin outputs – OC1A on D9 and OC1B on D10 – which is used is determined by the COM1A/COM1B settings. Even when using OC1B, as I am here, it is still the match value in OCR1A that determines when the counter has reached its “top” value.

I updated the code to try each of the above values for OCR1A in turn and the result is the video at the start of this post.

void setClock (int clock) {
  OCR1AH = 0;
  OCR1AL = clock;
}

Closing Thoughts

It is interesting to note that the Arduino can in fact provide a clock that allows the SP0256A-AL2 to function, even if it is not particularly true to the original at this point.

But it does mean that there isn’t as much control over the pitch as I’d hoped. If I want to get to more of that granularity between 4 MHz and 2 MHz, I’ll have to find another way.

Kevin

#arduinoUno #define #sp0256aAl2

Testing out the SP0256A-AL2 emulation on the RP2040 now.

#RP2040 #SP0256AAL2 #ShallWePlayAGame

SP0256A-AL2 Speech Synthesis

I had one of those moments recently when reading an article online sent me into a bit of a major tangent. The article in question was talking about the SP0256-AL2 speech synthesizer chip. And if you heard a computer talking in the 1980s, then chances are it was probably this chip doing all the hard work.

These aren’t very easy to come by these days, but you might get lucky with the usual places and find a legit, used, working one, but apparently an awful lot of those that can be found online are likely to be fake (see: https://www.smbaker.com/counterfeitfakejustplainbad-sp0256a-al2-chips).

But a number of peripherals for home computers in the 1980s included it and as luck would have it, the wonderful “MR GELÉE’S TECH” has a PCB, supplied with the chip included, for the RC2014 here: https://www.tindie.com/products/mrgelee/mg005-speech-synthesiser-designed-for-rc2014/

Update: I’ve also spotted that there is SP0256-AL2 emulation in the RC2040 project too.

So whilst on particularly a musical project (at least, not at the moment), this details how I got it up and running.

For my series of projects driving this from an Arduino, see Arduino and SP0256A-AL2.

https://makertube.net/w/gmqV2pM5UMqTPt31ThwseY

Warning! I strongly recommend using old or second hand equipment for your experiments.  I am not responsible for any damage to expensive instruments!

If you are new to microcontollers, see the Getting Started pages.

The SP0256A-AL2

This is a pretty amazing device. It was present in the Currah uSpeech peripheral (that unfortunately I never had myself) back “in the day” and a whole load of other cheap(ish) add-ons for 1980s computers.

It works by having a set of samples encoded in ROM for the basic phonetic sounds of the English language (called “allophones”). Then it is told which to sound by a controlling CPU, or these days MCU probably.

Of course, text to speech has come on enormously since then, and there are all sorts of nuance now possible. It will be interesting to see if the recent rounds of AI use become a pinnacle of text to speech or a curse, but we shall see.

But there is something pretty nostalgic about hearing an allophone-based, lo-fi (by today’s standards) chip in action. And this style of voice is iconic for the sounds of computer voices used in films such as War Games, 2001, and The Forbin Project, among many others.

There is a complete run-down of the family of these devices here: https://en.wikipedia.org/wiki/General_Instrument_SP0256

“The SP0256-AL2 is perhaps the most commonly encountered variant. It contains 59 allophones primarily intended for use with English language phrases and five pauses in its internal 16 Kb (2 KB) ROM.”

There are full technical details in a datasheet and application manual available online, for example, from here: https://www.cpcwiki.eu/index.php/SP0256

Here is the full allophone table from the datasheet:

The datasheet also includes some words that show how the allophones can be used, for example:

I sort of imagined that somewhere there might be a library that has the data structures that represent the details provided in the datasheet, but I’ve not found it yet if it exists.

But thankfully there are means of getting allophones from English Text, which I’ll get to shortly.

The Basic Code

The code to drive the chip from BASIC is pretty straight forward. This is my code based on the example provided in the manual:

10 DATA 18,12,55,12,43,18,51,35,5,55,0
15 DATA 24,35,46,52,45,21,41,51,11,13,14,53,45,0
20 LET LE=11+14
30 DIM XX(LE)
40 FOR Y = 1 TO LE
50 READ XX (Y)
60 NEXT Y
70 FOR Z=1 TO LE
80 IF (INP(31) AND 2) = 2 THEN GOTO 100
90 GOTO 80
100 OUT 31,XX(Z)
105 NEXT Z

There is a list of the phonemes required and they are sent to the chip in turn.

As already mentioned of course, the real trick is how to get that list of allophones. Whilst it is possible to walk through the datasheet for the SP0256A-AL2 and pick out the correct ones in turn, that is a lot more difficult that it might initially seem, as it perhaps highlighted above.

Text to Allophone Data Workflow

As with may of these things we are fortunately that there are tools out there that can do all this for us. In this case, two tools are required:

• lexconvert: https://github.com/ssb22/lexconvert
• espeak or espeak-ng: https://github.com/espeak-ng/espeak-ng

I used espeak-ng which has a MSI installer for Windows, and lexconverter which is a python script.

Install steps:

• Install espeak-ng as required. This is a command line utility for Linux or Windows and instructions for installation can be found in “Documentation” -> “User Guide”.
• Grab the lexconvert.py script.

I had to ensure that the location of espeak-ng was present in my system PATH, but also had to edit lexconvert.py to change several instances of espeak to espeak-ng. There were three places that looked like they would need changing, all associated with “os.system”, “os.popen” or “subprocess.Popen” calls or similar.

I suspect copying the original executable to a more handy location and renaming it to “espeak” would probably work too.

To get allophones suitable for use with the SP0256A-AL2 requires the “cheetah” option to lexconvert, as detailed below:

cheetah : Allophone codes for the 1983 "Cheetah Sweet Talker" SP0256-based hardware add-on for ZX Spectrum and BBC Micro home computers. The conversion from phonemes to allophones might need tweaking. Set the CHEETAH_SYM environment variable to see the mnemonic symbols from the instruction sheet (not actually used by the system).

The command I used was as follows, which then waits for keyboard input and creates a data structure of allophones which can be used almost directly in the BASIC program.

C:\Users\Kevin\Stuff>python lexconvert.py --phones cheetah
Enter text (EOF when done)
Hello World
DATA 27,51,45,53,46,52,45,21,0
Greetings Professor Falcon
DATA 36,14,19,13,12,44,43,9,14,51,40,7,55,52,40,26,45,41,51,11,0
Would you like to play a game?
DATA 46,30,21,25,22,45,6,41,13,51,9,45,20,51,36,20,16,0
This is the Voice of World Control
DATA 18,12,55,12,43,18,51,35,5,55,24,35,46,52,45,21,41,51,11,13,14,53,45,0

C:\Users\Kevin\Stuff>

One issue I had in using these DATA statements directly is that they get capped when pasted into the RC2014 terminal, hence using two DATA statements in my final code.

But in general terms, this works surprisingly well.

RC2040 Support

After getting this far, I happened to spot that there is also SP0256-AL2 support in the RC2040 emulator too – more here: https://github.com/ExtremeElectronics/RC2040

In particular there is a script that will create the entire BASIC code for you here: https://extkits.co.uk/sp0256-al2/

Full details of the emulation can be found here: https://github.com/ExtremeElectronics/SP0256-AL2-Pico-Emulation-Detail

This is a really easy way to start messing around with it.

A Note on Chips

As mentioned at the start, getting hold of a true SP0256A-AL2 might be a bit of a lottery, so it maybe that playing with the Pico emulation is good enough.

But a good source, if you are already an RC2014 user, is the MG005 as previously mentioned. It is a great addition to your RC2014 system.

In my case I have managed to end up with three devices, one from the MG005 and two off ebay. They weren’t particularly cheap but look like they come from sellers who have a range of vintage devices for sale (one in the UK and one from Netherlands).

All three devices do seem to work and seem to be actual SP0256A-AL2 devices rather than a re-badged simpler device in the range. Here are some photos of the tops and bottoms of my three devices.

The bottom one is the trusted source from MG005 (hence the coloured in GI logo), the others are the two ebay purchases.

They all have similar markings. The text appears pretty distinct in all three devices, and although it’s quite hard to see in the photo, all three have a faint “C 236 20” type marking, viewable in the right light, that is just visible on the centre device in the photo.

All three also have a very distinct, recessed, spot marking pin 1 and none of them seemed to have overly shiny pins that would imply they’ve been “re-dipped” in solder to make them look new.

So far, I think I have three good chips I can use for experimenting.

Closing Thoughts

I now feel like I should build up DATA statements of allophones for well-known quotes from computers in films.

I also now want to work out how to drive the SP0256A-AL2 directly from a microcontroller myself, so that will probably be next.

Then I would like to tie this up to MIDI somehow, but my initial thought, of linking allophones to MIDI notes, seems to have been done already: https://rarewaves.net/products/midi-narrator/

But I still might have to overdub it saying “Concerto for a Rainy Day”. Getting it in time with the music might be an interesting challenge, but maybe there might be a computer-voice-vocoder-like thing possible now.

And of course, this now presents all sorts of interesting possibilities for some more Philip Glass…

Kevin

#rc2014 #sp0256aAl2 #speechSynthesis