MozMo : the brilliant Arduino Mozzi synth in an Eurorack hardware.

The idea

Mozzi by Tim Barras is an outstanding library that allow the Arduino to produce complex and exiting sounds with almost no additional hardware.
(In fact MozMo uses the hifi mode that requires … 2 resistors and a cap !) The idea was to build a dirty cheap modular synth exploiting the vast potential of this library.


  • Arduino compatible with Usb connection
  • Powered via Doepfer 5v bus or via Usb (via jumper)
  • Uses Mozzi Hifi mode
  • 2 potentiometers
  • 2 CV entries
  • 1 gate entry
  • 1 audio out
  • Depth : 40 mm
  • Size : 6 hp





Here is one example

Check my Soundcloud for more demos



Examples sketches

I am building a collection of Mozzi sketches adapted for this module.
(wait for the page to load as there a few Soundclouds files embedded)
You can help me to build this collection by sending me your best sketches.


All the hardware files and the Arduino sketches are kept under my Github repository


If you plan to build one, have a look a this


I keep a few pieces of each components and I can ship :

  • pcb
  • panel
  • programmed Atmega328p
  • full kit
  • assembled module


  • re label panel entries A2 A3 and pots A0 A1
  • install onboard 5V regulator

Talkie Eurorack Module – Part 2 : Schematic & Pcb


Here is the schematic. Nothing really special : A simple RC filter I have used before with the Talkie library and a few pots to fiddle with the various functions. All the entries (cv and gate) are now protected with diodes to allow connections with modulars synths modules using higher voltages. A simple 7 segment to show the current playing mode. I plan to use the dot as the clock led

Talko1 0


I am ordering 8 Pcb from Beta Layout.
Here is the preview I got by uploading the file to their web site

20141228 0832 bot gold with mask with silk


Added female voice used in the talking clock

New sound demo

Here is the setup : a clock with variable pulse width is triggering the sound and stepping a sequencer feeding cv to the module. A bit of reverb is sometimes added just for fun

More demo on my Soundcloud


You can find all the files (hardware & software) on my Github


  • To share the Mouser cart
  • Module assembly
  • Eurorack Panel design

Talkie Eurorack Module – Part 1 : Concept


This arduino based module works thanks to a clever library : Talkie from 

I have already used this library to build a Talking clock

It is so simple to use that building a sound module requires only 5 pots and a button to get going.


I have slightly modified the original library to allow hacking it with various pots. The code is hosted on my github I edit the code and library directly from my favorite IDE : UECIDE




For the moment I have added 4 modes or sound banks :

  • digits
  • voltmeter (reading the CV voltage)
  • frequencemeter (fake mode just saying “Hertz” instead of “Volts”)
  • alphabet
  • nato alphabet

I plan to add a 5th mode with a large vocabulary and a 6th mode with weird sounds


CV signal change the words or phrase to be said


Pressing the button start the complete sound in trigger mode. (regardless of it’s length)
If the trigger switch is off, the gate will start the sound and hold it as long as the gate level stays up. Very useful to create crazy rhythms.

If the cable is plugged in, the gate is triggered via an external signal


Choose between trigger mode or gated mode


If bend is on, the bend pot … distords the sound.


Change the speed


Change the pitch


First test of the differents functions. Manual gate via a button

Looping a sequence in Ableton Live to trigger gate & cv while I play with the mode /speed /pitch / bend knobs


I am now working on a PCB and a panel.
I will upload these details and the schematics in a next post.

SSI 263 text to speech in Python via Nanpy on the Arduino

The almighty SSI-263 speech synthesizer chip

As you can read on the Wikipedia page, the SSI-263 is the other name for the Votrax SC-02.
It is becoming quite difficult to find, much harder then it’s little brother the Votrax SC-01 but I finally got one by buying a Mockingboard B on Ebay.
The SSI-263 is TTL compatible and need only very few component to be added. It is very easy to connect it to an Arduino but is much more complex than the Votrax-SC01 to program.


As I planned to make many software iteration and process the text to speech routine from Python, I decided to use Nanpy on the Arduino to « relay » the instructions to the chip. I guess I could also use Firmata to do the job as I am using really basics stuff like writing bytes on various pins.


The SSI-263 datasheet is quite easy to find and so the programming guide via some Google search but the best one I found is the Votrax SC-02 version that has an extra page at the end with a nice and very simple schematics to get started with .

As I plan to build a shield for the Arduino, I started to draw this in Eagle too :


You can download the Eagle version here
The chip needs a 1-2 MHz clock signal. I am using a Attiny 45 to do the job because all the timer pins are already in use on the Arduino. I have described how to use the Attiny45  to do this in a previous post


The best reference to get started is the article from Steve Ciarca : “Build a Third-Generation Phonetic Speech Synthesizer ».
A complete version is available on Google books. Ciarcia, Steve, “Build a Third-Generation Phonetic Speech Synthesizer,” Byte, March, 1984, p 28. (SSI-263)
There is also a reference to the SSI-263 and to many other speaking chip in “Chip Talk: Projects in Speech Synthesis” but the chapter mainly refers to Steve’s article.
The book is still available in some second hand book shop (I got mine via Amazon). The information provided is minimal but it’s fun to ready about all these veterans speaking chips.
Prochnow, Dave, Chip Talk: Projects in Speech Synthesis, Tab Books, Blue Ridge Summit, PA: 1987. ISBN is 0-8306-1912-7 (hard cover) and 0-8306-2812-6 (paperback).
Have also a look here : The page is regularly updated and makes an excellent starting point.


Here is the  Main code

The text-to speech is performed via a lookup in the CMU Dictionary (The dictionary can be install with these instructions :

It return an arpabet version of the text which is then translated into the Votrax allophone table.
(thank to this modified Arpabet to unicode script)
The allophone chain is then sent to the chip
The code is very basic and doesn’t use the SSI263 registers to their full potential : the voice generated is very robotic … but I like it a lot


Listen to the chip saying the Issac Assimov’s 3 laws of robotics with 2 different voice settings :


Next thing I will try is to add prosody or even make it sing
On the hardware side I plan to add a RC filter with  an amplifier and add a midi in to the circuit .. so stay tuned.

SN76489 arduino shield – part 1 testing the chip

I always loved to play with sound making chip back in the ’80 (I made a synthesizer with the SN76477 in `79 which is sill working)
Today it is still possible to buy some SN76489 on ebay and a few website are decribing how to connect the chip to an Arduino.
The most advanced code is offered by for the Teensy and for the Arduino


The SN76489 needs a clock signal that must be provided by an external oscillator. As I coudn’t find one, I decided to program an Attiny45 to do the job.
The code offered here is for the Attiny15 but the Attiny45 can be configured into an Attiny15 by programming the CKSEL fuses to ‘0011’ (see the datasheet)
The AVR assembler code need to be slightly adapted to calibrate the timing of the signal with the help of a frequency counter. I plan to play midi note in tune with other devices, but if you don’t need an exact tuning you can use the file as it is : the Attiny45  is providing a clock signal at around 2Mhz on pin 6.
I am using gasvr on the Mac to assemble the .asm file into an .hex that it uploaded to the Attiny with AVRfuses.
(Download the compiled clock file here and rename the it to clock.hex and use it to flash the ATtiny45)


Connecting the Arduino and the SN76489 is described in the Arduino code here
Now we need to send midi data to the Arduino via the usb port
There is ready made solution for Mac, Windows and Linux : the Hairless midi to serial bridge !
(Don’t forget to adapt the baud rate in the preferences to the one you are using in the Arduino code)
If you don’t have midi sequencing program you can use midi virtual keyboard like :
Here is a first sequence I sended to the chip with Ableton live (a midi file found here :

Arduino talking clock

I’ve discovered this great library here 
They have done an impressive job. The library is provided with a large vocabulary.
It is a software implementation of the Texas Instruments speech synthesis architecture (Linear Predictive Coding). It is just amazing to discover what  the atmega168 can do. By the way the library works only with 168 and 328 16MHz based Arduino.
Just for fun to hear the script counting …

And then the clock saying the time

To build this clock you need :

  • An arduino Uno
  • A temporary switch
  • A speaker
  • A DS1307 clock
Talkie clock bb

I plan to add and infrared detector to allow the system to say the time by just waving a hand in the dark.
I have mixed the example code provided in the talkie library to process and say numbers (Volmeter) and the vocabulary from the Vocab_US-Clock example.
The sketch wait for the button to be pressed and then read the clock’s time.
It first greet the listener for the moment of the day (morning,afternoon, evening) and then say the time

Votrax SC-01A PWM clocked

The idea

I got this brilliant idea by John Loadsman who is using a version of my previous code:

I also wanted to digitally control the Votrax’s pitch to implement some new functions. (keep in mind that I want the Votrax to sing)

The hardware modification was pretty easy: I removed the analog clocking part, tied the MCRC to the ground and just pulled the Votrax’s clock entry MCX to +5v with a 2.2k resistor.

I had to use pin 3 on the Arduino to produce the clock via the timer 2 and, therefore, need to use pin 6 for the A/R


What’s new

– Moved the A/R to pin 6
– Using pin 3 to generate the clock (see setup section)
– Created a function to drive the clock on demand. See ClockFrequency() where the clock frequency is given in kHz.
– note: My Votrax doesn’t seem to accept a frequency bigger than 910 kHz
– Added some new modifier _PITCHUP & _PITCHDN to allow variation within the text

Todo :

– find a way to produce musical notes
– Add midi control



SP0256-017 says some numbers and plays little melodies

I just received an SP0256-017 purchased on Ebay as the one on this picture from Flickr.

SP0256-017 Speech Synthesis Chipset (Mint In Box!), 1983

This version of the SP0256 was designed for talking clocks. I work with the help of a dedicated EPROM which hold the code for the numbers (without the EPROM, it can say the numbers from 0 to 10 but then it hangs). This version cannot says the allophones as it’s bigger brother the SP0256-AL2 variant

I found the data sheet here but the quality of the scan is quite poor. I used the schematics from the SP0256 to understand what to do.

The sound are quite funny and I couldn’t resist posting a little message just to let you ear this chip.

Oh Eighteen
One Nineteen
Two Twenty
Three Thirty
Four Forty
Five Fifty
Six It is
Seven A.M.
Eight P.M.
Nine Hour
Ten Minute
Eleven Hundred Hour
Twelve Good Morning
Thirteen Attention Please
Fourteen Please Hurry
Fifteen Melody A
Sixteen Melody B

Melody C

I just coded a loop to ear this table.

Votrax SC-01A (tries to) sings

Having a working Votrax SC-01A hooked to an Arduino, I wanted to test the inflection bits to hear their influences on the speech.


To get the inflection working we need to toggle the to inflection bits low or ligh. The Votrax’s inflection entries are CMOS level, so we need to adapt them for the arduino (see The two entries are forced to high via 2 resistors and connected to the Arduino pin 4 & 5 (see code at end of page).

Votrax using inflection via Arduino

Inflection setting are pretty coarse : toogling the inflections bits gives a strong variation to the voice. I plan to add a digitally controlled pitch using a LTC6903 as done with the SP0-256 AL2. See

In this first example you can hear the Votrax variation in pitches.(I got some inspiration on the code thanks to the excellent works done for the GinSing shield. See GinSing library & examples V3.0)

Holding vowels & inflection changes

To try to sing, I also added somes delays to force hold the vowels in an attempt to mimic Kraftwerk style


Manual Timing

Finally I added a potentiometer and a switch to replace the normal and individual phoneme timing by an artificial one to make it sound more robotic. If the switch is on, the sketch read the pot value and force all the phonemes to be sustained for certain time (from 30 to 300 ms)



Here is the code :


Arduino midi in interface

Took me quite a while to finalize my midi in interface !

A lot of time wasted because I used a MCT2 optocoupler with  the “standard” 200 ohms resistor on the incoming signal.

The output form the optocoupler to the arduino was quit weak (thanks to my old oscilloscope). I finally found the solution in the  MCT2’s data sheet : the input LED needs a 60 mA current ! (as opposed to the 25 mA for the more classical 6N13x series). You can use a 100 ohms resistor : it works fine.


I also wrote a little sketch to test the MIDI library : the led (attached to pin 3) blinks if a NoteOn, Program Change or a  Controller change is received.

You can also attach a piezo to pin 3 to play the note received

There is still a problem I have to solve : the library doesn’t responds directly after reset : it need to receive a program change first or a controller change before reading any data. Any ideas why ?