Motion sensing for Midi project question

[ChrisW]

Hey guys,

I am contemplating a diy midi keyboard project but am not sure how to sense and measure the timing of the movement of the individual keys in an accurate manner.

Would hall effect sensors work or would I have to design some light based solution like an led and photo-diode?

Any pointers would be greatly appreciated!

-Chris

[Memphis]

Hall-efect sensor is reasonable but much better would be an accelerometer for each key. Todays accelerometers can be chained with one bus I2C or SPI and thus you can easily process it with for example ATmega168.
I was playing with midi on University and this was a result: Industrial orchestra 

[Hideki]

I think you will find it very hard to get any sensible data out of an accelerometer without a lot of processing. It will also require running wires to every key, unless the intention is that the key actually hits the accelerometer at the end of its travel. It might be fine for a more percussive type of instrument. Determining if the key is actually up or down also gets a bit tricky.

The usual way to do it is to have a pcb with two contacts per key. A silicone membrane strip sits above it with two carbon pill contacts per key. One is a bit higher than the other, so as you press the key down, one switch closes before the other. You measure the time between them to determine the key velocity.

It's used by nearly all midi keyboards on the market, but I guess it's very hard to DIY that at home.

There are optical methods, like pnoscan. http://www.midi9.com/products.htm based on reflective optical sensors like http://www.digikey.com/product-detail/en/QRE1113GR/QRE1113GRCT-ND/965713

Hall effect should work fine too, but then you need to put a little magnet in every key.

[jmole]

My advice:

Forget about a DIY keyboard unless you're trying to do something totally new, like the Continuum, or ROLI.

Pick one up at your local pawn shop, it will save you lots of money. Then, hack on whatever other functionality you want by hacking on the MIDI stream.


But, if you're still considering it, check out a related project I did a while back: http://portfolio.moeller.io/happy-feet.html

I'm sure you can adapt the pressure sensing technique to whatever you're looking to create.