Walmart piano keyboard

Thread Starter

m3770

Joined Jan 18, 2023
3
I had purchased a cheap Walmart piano to play around with my music creation and have some options other than bass/guitar. I have been learning oscillator circuits and made my own effect pedal, so when the main chip started acting like it got burned out, I wanted to use the key circuit board section with a 555 timer or similar circuit. I do not, however, know how the contacts are connected to produce the signal path when pressed, due to no available pinout of the main chip. How would I go about finding the paths so I can connect it to an oscillator circuit to produce at least a part of the keys' worth of signals?
 

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Ya’akov

Joined Jan 27, 2019
9,237
Welcome to AAC.

The keyboard is using a switch matrix arrangement. It is hard to tell how it is being implemented from your photos. If you could take a sharp, well lit full length photo of the entire keyboard it would help a lot. Failing that, if you could take two or three such photos with a slight overlap from the same angle above that could be reconstructed into a full view, that would work too.

However it is wired, you have a bit of a dilemma. In theory, you could use a diode martix to decode the keyboard. This would be complicated and extensive, though. The right solution is an MCU (MircroController Unit), like an “Arduino” that could very easily do that, but using the output of the MCU to turn on 555-based oscillators is frankly silly.

The MCU can produce whatever waveform you might want. It can do other things too, like output MIDI from your keyboard. But, I know this is not what you wanted to do and perhaps it doesn’t seem to be a solution to your “problem”.

I am going to suggest that your problem isn’t making the keyboard operate 555-based oscillators rather it is learning techniques to reuse the keyboard and other things that add to your knowledge and practical skill. WIth that reframing, learning to interface and program MCUs in the Arduino ecosystem is a very highly productive activity.

The possibilities are effectively endless with the Arduino and other MCUs/ecosystems. While I don’t think you should abandon circuits, which is a vital area in electronics, I do think you should add the modern and amazingly flexible world of MCUs and the cheap, ubiquitous, effective Arduino ecosystem to your knowledge as well.

In the end, with the skills you can learn in the MCU world, you could take a small, cheap, integrated circuit and create a decoder for something like what you are working on easily, even if you use discrete logic as the consumer of that decoding.

This means you can take something like a $5, 24-pin chip and program it to be the decoder as if it was a custom IC—this is very cool and has all sorts of applications, obviously. But, for the start, leaning on something that has more capacity and peripherals will make learning easier.

However you decide to do this, good luck with it—but in spite of your presentation of the problem it is my considered opinion your attempts to use the keyboard to switch discrete 555-based oscillators will end in tears. Even if you manage to do it, the complexity of the decoding matrix implemented in hardware will ensure that the project being over is your favorite part of it.

While a more experienced person who could picture the solution in hardware and set about doing it would find it a tedious but trivial thing, for a neophyte, it will quickly become a tangled web of crossed wires and confused parts. On the other hand, the satisfaction that the hardware/software combination of the MCU world brings to both expert and neophyte alike is prodiguous.

Post the photos for more help on the switch arrangement, and if you are interested in starting on a path to MCU knowledge, let me know.
 

Thread Starter

m3770

Joined Jan 18, 2023
3
Welcome to AAC.

The keyboard is using a switch matrix arrangement. It is hard to tell how it is being implemented from your photos. If you could take a sharp, well lit full length photo of the entire keyboard it would help a lot. Failing that, if you could take two or three such photos with a slight overlap from the same angle above that could be reconstructed into a full view, that would work too.

However it is wired, you have a bit of a dilemma. In theory, you could use a diode martix to decode the keyboard. This would be complicated and extensive, though. The right solution is an MCU (MircroController Unit), like an “Arduino” that could very easily do that, but using the output of the MCU to turn on 555-based oscillators is frankly silly.

The MCU can produce whatever waveform you might want. It can do other things too, like output MIDI from your keyboard. But, I know this is not what you wanted to do and perhaps it doesn’t seem to be a solution to your “problem”.

I am going to suggest that your problem isn’t making the keyboard operate 555-based oscillators rather it is learning techniques to reuse the keyboard and other things that add to your knowledge and practical skill. WIth that reframing, learning to interface and program MCUs in the Arduino ecosystem is a very highly productive activity.

The possibilities are effectively endless with the Arduino and other MCUs/ecosystems. While I don’t think you should abandon circuits, which is a vital area in electronics, I do think you should add the modern and amazingly flexible world of MCUs and the cheap, ubiquitous, effective Arduino ecosystem to your knowledge as well.

In the end, with the skills you can learn in the MCU world, you could take a small, cheap, integrated circuit and create a decoder for something like what you are working on easily, even if you use discrete logic as the consumer of that decoding.

This means you can take something like a $5, 24-pin chip and program it to be the decoder as if it was a custom IC—this is very cool and has all sorts of applications, obviously. But, for the start, leaning on something that has more capacity and peripherals will make learning easier.

However you decide to do this, good luck with it—but in spite of your presentation of the problem it is my considered opinion your attempts to use the keyboard to switch discrete 555-based oscillators will end in tears. Even if you manage to do it, the complexity of the decoding matrix implemented in hardware will ensure that the project being over is your favorite part of it.

While a more experienced person who could picture the solution in hardware and set about doing it would find it a tedious but trivial thing, for a neophyte, it will quickly become a tangled web of crossed wires and confused parts. On the other hand, the satisfaction that the hardware/software combination of the MCU world brings to both expert and neophyte alike is prodiguous.

Post the photos for more help on the switch arrangement, and if you are interested in starting on a path to MCU knowledge, let me know.
Thank you, I actually have been self teaching what I know so far this past year or so. I haven't jumped into micro controllers and arduino yet mostly because of budgeting priorities, but I have looked into it. I kind of figured it wouldn't be as simple as just a couple connections, but figured I'd see what the best options were for the job. I can take the picture/s when I get back home tomorrow for the sake of being thorough.
 

Ya’akov

Joined Jan 27, 2019
9,237
Thank you, I actually have been self teaching what I know so far this past year or so. I haven't jumped into micro controllers and arduino yet mostly because of budgeting priorities, but I have looked into it. I kind of figured it wouldn't be as simple as just a couple connections, but figured I'd see what the best options were for the job. I can take the picture/s when I get back home tomorrow for the sake of being thorough.
You can start in the Arduino world surprisingly cheaply. There are clone boards that are literally just a few dollars, and sensor/actuator kits for learning similarly priced. If you wait, AliExpress can provide very low prices at the cost of longer shipping times.

If you want to get started, and would like specific recommendations, I would be happy to make some.
 

Thread Starter

m3770

Joined Jan 18, 2023
3
for someone who has a good bit of computer experience, and a little "programming" experience but nothing professional, I'll take whatever you have in terms of suggestions. Actually was looking into the different kits and figuring out what I wanted to do a little ahead of time. I would love to do something that would interact with my guitars or effects pedals, I assume that would involve some midi control, but ultimately, would love to have basically a custom "synth keyboard" type of setup with that board. I will upload full pictures of it later today
 

MisterBill2

Joined Jan 23, 2018
19,032
Why do you think that the main chip is "burned out"? That is not likely unless excessive supply voltage was applied.
A broken connection is much more likely.
 
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