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Text-to-speech with the SpeakJet! (SpeakJet revisted)


This blog article describes an easy way to add unlimited speech to your Arduino projects (PicAxe, BS2, or any other microcontroller for that matter). It goes beyond simply adding a SpeakJet, which  is a popular (and common) approach, however the SpeakJet can be a bit tricky to program. Wouldn't it be great if the SpeakJet could just say what you want it to, without spending so much time looking up the speech codes to simply speak a few words? In my previous blog I used PhraseALator software to help, but PhraseALator is limited to the words stored within it as well.

Apparently I could take either a software approach or a hardware approach to add text-to-speech to the SpeakJet. At this time, I don't know where to find a software "text-to-speech" solution for the SpeakJet, and I don't have the time to develop one - but someone did beat me to it by putting "text-to-speech" onto an IC! So this is my hardware solution! By adding just one additional IC to my original circuit (the TTS256 Text-to-Code processor) we now have text-to-speech capability for the SpeakJet! Adding speech to your projects is almost as easy as simply typing what you want it to say. One of the benefits of this approach is it requires very little from the Arduino as far as I/O and memory.

Parts needed (if you built the prototype from my first blog posting you will have nearly all of these parts). Most of the parts should be available through most large electronics retailers on the web (such as DigiKey, Mouser, or Jameco). Where they are not, I've added links to the component.

1 - Arduino (Refer to Arduino website on where to buy and how to setup your Arduino. For the first video, I used an AdaFruit BoArduino, but you could use nearly any Arduino or Freeduino clone.)
1 - SpeakJet
1 - TTS256 text-to-speech processor
1 - LM386N amplifier IC
2 - .01uF capacitors
2 - .1uF capacitor
1 - 10uF electrolytic capacitor
1 - 100uF electrolytic capacitor
1 - 10K resistor
2 - 27K resistors
1 - 10K potentiometer (set to approx middle of range to start)

My schematic is based on information and examples shown in both the SpeakJet (pdf) and TTS256 (pdf) user manuals. Essentially this is a modification to my earlier blog posting with connections added to accomodate the TTS256. This is the schematic that I built this project from...



 A larger image of schematic is available below (just above the comments) as a file attachment...


This is a photo of the project I built on a couple solderless breadboards:


The following sketch for the Arduino is an example of how to make this work. As you can see, just regular English text, no more mysterious looking speech codes! The first video demonstrates the sketch below. You can modify the text in the sketch to make it say almost anything you want!

// SpeakJet text-to-speech "All LMR are belong to us" demo

//set up a SoftwareSerial port for Speakjet Shield
//rxPin: the pin on which to receive serial data from TTS256
//txPin: the pin on which to transmit serial data to the TTS256
#include <SoftwareSerial.h>
#define txPin 2
#define rxPin 3
SoftwareSerial sjSerial =  SoftwareSerial(rxPin, txPin);

void setup(){
    // initialize the serial communications with the TTS256/SpeakJet
  pinMode(rxPin, INPUT);
  pinMode(txPin, OUTPUT);
  sjSerial.begin(9600);// set the data rate for the SoftwareSerial port
  delay(1000); // wait a second for the Arduino resets to finish (speaks "ready")
  sjSerial.println("All L.M.R. are belong to us!"); // send the text to speak to the TTS256

void loop()

I have found the TTS256 does a pretty good job with most English words. Some you have to "creatively misspell" in order to get it to sound correct. One example I found right away is "robot". Apparently "robot" is an exception to the phonetic rules written into the TTS256 as it comes out sounding more like "raw bot" rather than "row bot". Such is life, sometimes when working with small micros such as the Arduino or PicAxe you have to put up with a little quirkiness. :-) For speech in my projects I can put up with a little misspelling once in awhile!


Also, with the circuit as shown here, it is pretty easy to "overflow" the SpeakJet buffer with too much text (the SpeakJet will either stop speaking, or spews out random words from your text). Adding a few well placed "delay(milliseconds)" functions help, but you could also monitor the SpeakJets "buffer-half" or "d1/speaking" lines to determine when you are about to overflow.

The photo below and second video show an Arduino shield PCB I made based on the above circuit. I have added more noise shielding, headphone/speaker connections, busy/buffer-half monitoring and easy switching between the SpeakJet and TTS256 configurations to it. At this point, I don't know how much interest there may be in LMR-land (and beyond) for this shield, but I can make boards/kits available if there are enough people interested in buying one...


 2009-11-29 UPDATE!

 I was not happy with how my schematic image rendered above. Since apparently LMR won't let me post a higher-res (greater than 500x500 pixel) version, I changed the image colors a bit to at least try to make it more readable. I re-uploaded the schematic image - yeah it's still smallish, but at least (to me anyway) a bit more readable than my original. Later I will add a link to a higher res image when I figure out how...

 2009-12-1 UPDATE!

I made this post a tip/walk-through (after a bit more editing). I have also linked a larger schematic to both postings. Sorry for the redundancy. I may delete this one later. When I first posted it here I wasn't thinking of it as a walk-through, but decided later that it obviously should be. Click here for the walk-through...

 2010-1-20 UPDATE!

Revised schematic uploaded.


SpeakJetTTS_Schematic.PNG26.54 KB

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m sry for posting it here.....bt i seriously need help

i am an engineering student..in electronics and communication....m literaLYY zero in robot making etc....bt i realy hv an interest in dis...

i hv to make a project on text to speech convertr....plzzz help me out ...i just hv 3 days to submit synopsis

Nice hit with Make Blog! Good for you!

I have noticed they are mentioning Cantarino as a candidate for speech synthesizer. I think Webbot's work is much better and more close to what SpeakJet does. Perhaps even the sound effects can be done, but I didn't work on that yet. I have a preliminary library that has only say(text), speak(phonemes) and setPitch(number) commands. I need to add the possibility to print out the phonemes after converting from a text string (Webbot had them in his original code for debugging purposes, I just deleted them to make the code smaller), so one can play around with them to get better results. 

Anyway, I can't add files to your topic, so I'll add the library to mine, get it and test it out, see how it does. The library is in a zip file, rename the file to TTS.zip then unzip and copy to your libraries folder.




Hi Ro-Bot-X. Thanks! It was a bit unexpected, although nice, but I thought of this project as being more of a nuts and bolts thing rather than something that would get much attention! Guess I was wrong :-) No complaints tho...

I managed to get the TTS.zip file from your MiniEric page. Will take a look to see if I can get it to run with my SpeakJet shield when I get the chance!


For those who haven't seen it yet: http://blog.makezine.com/archive/2009/12/text_to_speech_theres_a_shield_for.html Whoever passed it on to Make Blog, thank you!!

I will have a very limited supply of these as kits available to build and try out soon. The website link to order and for more information will be posted here shortly.


Congratulations on making it to the Make Blog!  

 I'd buy a kit if you made one.  You should also post to the make blog if you do make a kit, you'll sell quite a few of them I expect.  


I've just opened the droidbuilder store! Visit the main site at http://www.droidbuilder.com - take a look at the docs and order one from my store if you want one. I am working on getting some kits bagged and ready to ship, as I get my act together I should get some shipping in a day or two...
The questions asked so far are great fodder for a "frequently asked questions" section I want to add to my (future) store website. Keep them coming! :-)
Very nice! Very cool! But is it possible to add automatic buffer-monitoring abilities to the shield without too much trouble?

Thank you thank you! :-)

I do have buffer monitoring lines already implemented in the shield. I have connections available for both the SpeakJet "Buffer-half-full" and "Speaking" lines - whichever used is user-selectable. It only takes a couple of code lines in the sketch to implement it (although still slightly tricky getting the delay time right - getting the 'Daisy Bell' song in the demo to run correctly took me more than a couple tries!). I will admit there may be a better way to handle this, but at this time I am still learning more about the SpeakJet myself. But the lines have been made available to the Arduino, so as I (or we?) improve my technique - it should be nothing more than just updating a sketch.

For a few occassional sentences here and there, I find buffer monitoring isn't necessary. The buffer overruns happen mostly on long multi-sentence phrases or in songs. The most troublesome thing I can think of someone maybe throwing at this shield would be a twitter-feed, or reading out loud a book, but I don't (at this time anyway) think the problem is insurmountable.

I should probably also mention that the SpeakJet in this shield is "mostly implemented". You can throw speech/sound and almost anything else available via the serial connection at it. But I did not implement the "event" pins as these are for "stand-alone" applications and (to me) did not make sense to implement on a shield.


hi droid builder,
i've been looking at the speakjet chips for awhile now. this post is like manna from heaven for me. i would be very interested in a shield at some point in the near future