555 Astable Keyboard

The 555 timer is a powerful chip for a low cost oscilation system. By adjusting the components that you attach to it, you can make it oscillate faster or slower. Hook that to a speaker and you get a nice 555 Keyboard.

Here is the list of parts you will need. You can get them at any local electronics shop, or you can order them online.

1 protoboard
1 1k resistor
3 10k resistor (4 shown, found out you didn't need it when wiring up the circuit)
1 220 ohm resistor (not shown)
13 Tactile buttons
13 trimmer pots
1 8 pin dip ic socket
1 555 timer
1 .01 uf capacitor
1 .22 uf capacitor
1 9v battery clip
1 9v battery
1 8 ohm speaker

Tools needed:

Solding iron
Hot Glue
Wire cutters and strippers (not shown)

To start, orient your protoboard such that all the keyboard buttons fit onto the board with enough room for your fingers to play them. I put a single hole gap between each of mine, but depending how you want to lay out your board, you can make them closer or farther appart. I added 8 buttons to the bottom row, and 5 offset above. If you want it to look like a piano this layout makes sence. 

When you finish adding all the buttons, repeat this pattern about 3/4 to an inch away from you buttons. Following the same pattern will help make it easier to tune later on. For the first 3 buttons, the 10k trimmer is not big enough of a value for the 555 circuit, so add a 10k resistor. I originally had 4, and there are 4 pictured, you you only need three. Do not add the one farthest to the right.

Solder these onto their pads to keep them in place.

Then solder a long jumper wire to every other terminal on the buttons, meaning solder the wire to the right or left side of each button. but not the other side of each button. Try to keep this consistant. it will help you latter. 

Do this again with the potentiometers. This time solder all the pin 2 connections together on the bottom side of you board.

To begin your 555 circuit, i recommend that you breadboard it first. Test everything out and make sure that you're circuit is going to work before you start soldering. You will see the 555 circuit move at this point for me because i messed up. Lesons learned.

1. Solder a jumper wire from pin 4 to pin 8. The piins go ccw arounf the chip, with the little notch indicating the pin 1 location.

2. Add a jumper from pin 7 to the wire connecting all your buttons together on the bottom of your board. Add the 1k ressitor from pin 4 to pin 7. I just had it jump to the button leads because it was easier.

3. Add the .22 uf capacitor such that it is between pins 2 and 1. If you are using a polarized capacitor, have the negative side connecting to pin 1.

4. Add the .01 uf capacitor, connecting from pin 5 to pin 1.

5. Add the 9v battery clip by soldeing the positive lead to pin 8 and the negative lead to pin 1.

6. (had to meove the circuit at this point) Solder in the 220 ohm resistor. Connect one side to pin 3, and the other side move into an open area.

7. Solder 2 long leads to the speaker. Solder the negative lead to pin 1 and the positive lead to the end of the 220 ohm resistor not connected to pin 3.

For the last little bit of soldering, add a jumper from the buttons to the potentiometers. If the button is paired to a 10k resistor, jump to that first, then to the potentiometer.

When adding the jumper, solder to the opposite corner from which you soldered the jumper wire to. If you added the jumper to the left side of each button, connect the jumper to the right side of each button. Connect each button to it's respective potentiometer's pin 1.

To tune your piano, you can do it by ear. Using a small tone generator app on my phone, I adjusted each potentiometer to match it's respective piano tone. 

Now all that's left is to hot glue the speaker into place on an open section of your board, plug in your 9v battery and...

The piano is done! You should be able to hear your speaker oscilating and ouputing the different notes when you hold down the button for each key!