Standalone Makey Makey

Using Arduino Microcontrollers
1

hey

i need to make a 18 key touch sensitive musical keyboard.

i tried the MPR121 and it works great, but it only offers 12 electrodes. i cannot use the capsense library because they keyboard has to be far away from the arduino... the long wires mess with the capacitance readings.

so, the makey makey sounds like a great solution to my problems, but i need to be able to use it without a computer.

can anyone think of a solution where the makey makey can run in standalone mode, with each of the 18 electrodes switching 18 arduino pins on/off?

any thoughts would be greatly appreciated....
thanks !!

2

dataplex:
i cannot use the capsense library because they keyboard has to be far away from the arduino... the long wires mess with the capacitance readings.

Why not put the Arduino next to the keyboard so that capsense works then transmit the keypress information along long wires (where capacitance isn't much of a problem).

If necessary, add another Arduino at the other end to receive the information. If you do that then a whole bunch of other possibilities appear, like wireless communication.

3

@fungus

i cant fit my arduino mega inside the instrument im making... thats why a tiny MPR121 or a makey makey would make the most sense.

is there a way to use the makey makey as a standalone ardunio, controlling 18 logic pins?

4

dataplex:
@fungus

i cant fit my arduino mega inside the instrument im making... thats why a tiny MPR121 or a makey makey would make the most sense.

is there a way to use the makey makey as a standalone ardunio, controlling 18 logic pins?

Use two MPR121s?

5

okay, that would work.... hmmm.... any idea how i would do that? i cant find anything on the subject.... it seems i would have to change the address codes and whatnot...

6

The MPR121 datasheet shows how you can change the chip's i2c address by connecting pin 4 (ADDR) different ways:

4
ADDR
I2C Slave Address Pin Selects.
Connect to VSS, VDD, SDA, SCL to choose address 0x5A, 0x5B, 0x5C, 0x5D respectively.

so you should be able to use up to 4 of the chips on the same i2c bus without issue.

The other thing you can do is multiplex the input lines so a finger press really touches two sensor pins. This app note for the MPR 121:

http://cache.freescale.com/files/sensors/doc/app_note/AN4600.pdf?fpsp=1&WT_TYPE=Application%20Notes&WT_VENDOR=FREESCALE&WT_FILE_FORMAT=pdf&WT_ASSET=Documentation

has an example of a 7x5 grid; for your needs you could get by with a 2x9 or 3x6 etc.

Good luck!

[edit - fixed app note URL]

7

dataplex:
okay, that would work.... hmmm.... any idea how i would do that? i cant find anything on the subject.... it seems i would have to change the address codes and whatnot...

Yep. Each will need a different adderss.

It's easy to do, just a case of connecting pins to ground. Most breakouts even have jumpers for doing it, eg. SparkFun Capacitive Touch Sensor Breakout - MPR121 - SEN-09695 - SparkFun Electronics