Upgrade A Toy Keyboard’s Tone Production


[Jan] was given this toy keyboard and decided to make it the subject of his next project. In addition to having three octaves of keys it’s got a ton of buttons used to select different modes. He gave it an upgrade by installing his own tone production circuitry seen in the upper right.

His preliminary investigation of the stock components yielded a mystery uC encased in a blob of black epoxy. He wasn’t going to be getting anywhere with that, so he started by figuring out how to use 4051 multiplexers to read all of the keys. Outputs for that were routed to a 20 pin header for easy connection to the synthesizer board he would build in the next part of the project. He based it around an ATmega8, which we know can produce some killer chiptunes audio. Once he had everything working he laid out a circuit board in Kicad to ensure the transplanted circuitry would hold up inside of the toy keyboard. You can hear all of different effects it’s capable of in the clip after the break.

18 thoughts on “Upgrade A Toy Keyboard’s Tone Production

  1. I found one of these chinky keyboards in the trash. It ain’t even voltage stable tuning, it needs bent but has high cheese factor as is. I should try a manual generator with no voltage regulation no battery modest cap, a bit like bagpipes. Save your good work for a vintage organ key-frame that will hold up to further experiments, or make noise box out of the old innards.

    1. Perhaps a vintage organ is his next project. This one seems to have mainly dealt with key matrices and tone generation. That will prepare them for anything they run into with a full size organ and they will have plenty of space to deal with :) Not having a garage, currently, I can certainly sympathize with keeping things small scale.

    2. Hello.
      It is like Franklin says: this project was mainly about keyboard sensing and tone generation. And making custom circuit board at home. I like vintage organ being rebuild (I guess we all know the greatest of great – The Chipophone) but I actually don’t play piano, so my territory ratherr is small boxes with knobs – like Franklin is saying. So I like your idea of reusing old innards, it is still somewhere under table :)

      1. My brother from another mother :) Keep up the good work buran. There are so many of these My Music Center oriented clones out there that your current config will transfer to pretty much all of those lil keyboards out there :) Many use the 8voice 8drum 4drumpad config so just having that matrix mess already figured out saves a load of time and trial and error. Thanks again, buran! You may hear from me in the future as I am gonna be trying your guide out.

  2. “Once he had everything working he laid out a circuit board in Kicad to ensure the transplanted circuitry would hold up inside of the toy keyboard.”

    How does using a CAD program make a circuit more robust, and what conditions exist inside of a toy keyboard that would require it if so?

    1. The key here is that its not about how you design and make the circuit board but just that one is made that will fit neatly where the original was.

      A toy keyboard such as this can actually receive quite a bashing moving it from one surface to the next, throwing it in a backpack, dropping it, etc… Due to its scale its pretty portable, and these are all hazards. So if they had hot glued in a series of awkward shaped PCB in there, over time they would probably work free.

  3. Neat idea. My wife and I ban grossly — and unintentionally — out-of-tune tune toy instruments from the house. This policy has sent several keyboards to the thrift store. I might have to look into doing something like this project to the next torture device^B^B^B^B^B^B^B^B^B^B^B^B^B^B keyboard gifted to my daughter by my tone-deaf in-laws.

    I especially love that the PCB appears to have screw holes to mount to the (I assume) existing bosses in the case. That’s a nice touch. Are those full-sized keys?

    1. Hey man ya could maybe just bend them back in tune. More importantly (at least to my friends with kids lol) is the addition of a volume pot to any child’s toy. If you ever need to find a home for one of these random outta tune fellas, feel free to let me know :)

      1. If you add the volume pot (or two), I would personally make sure that it (or one) is recessed inside the enclosure, accessable only with a “tweeker” type tool (or screwdriver if completely internal). That way, you can set the maximum volume. My son seems to think there are only two volumes: off and maximum. I generally don’t want to hear out-of-tune, poorly-played, cheap-synth “music” at whatever volume the designer thinks is a proper level.

        1. Excellent point, Brian! When dealing with toddlers and wee ones that like to eat anything they can, you have to be very careful about the selection of pot if it is to be exposed to a child’s creepy nimble fingers lol. I would feel awful if a kid or baby pulled off a knob and ate or choked on it :( So glad you brought up that point and your suggestion of the trim pot/micropot is perfect! I have been using side wheel style tweak pots usually on the back of the instrument, but your idea will save me breaking out the dremel lol. Admittedly, a simple internal limiting resistor would probably be the safest and best bet. And I would agree that the kidtunes do get old real quick lol. Thanks :)

      1. I almost mentioned the crappy sounds this model originally produces lol. Being a circuitbender and tinkerer, I am pretty familiar with working models of this and ugh, very grainy dither zipper for the envelope and 4 variations of the same sound lol. I have seen models that have an echo/vibrato effect built in and one without drums that had 2 sounds and 18 demos lol. They are pretty rough but I did learn a lot about low pass filtering trying to clean them up. It is amazing how much better some of these sound with a simple lpf at the amp or output. I have to ask again if we were separated at birth lol? I like your sounds much better, buran.

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