The electronics for the xylophone are setup identically to the Fritzing circuit diagram on the Electronics page. The ItsyBitsy will live on a 1/4 Perma-Proto and then three 1/2 Perma-Proto boards will be used for the MCP23017's and the four ULN2308's.
One board will have the two MCP32017's and then the two remaining boards will have two ULN2308's each. To begin wiring, solder the IC sockets onto the boards. Then, run the wires for power, ground and I2C.
Mount the boards to the xylophone. The screw ends of the M3 stand-offs are facing out so that they can slot into the boards' mounting holes and then be secured with some M3 nuts. By doing this, you'll know exactly how long the wires have to be between the multiplexers and drivers, followed by the driver boards and the solenoids.
All of the outputs from the multiplexers will connect to the inputs of the drivers, which should be oriented to face towards the bottom of the xylophone. This way, the outputs of the drivers will be at the top and easier to access for the solenoids.
The solenoids will connect using a JST extension cable. Cut them to length based on the location of the solenoid and the driver output.
Don't get rid of the other connection end though! They'll come in handy for future projects. You can never have too many JST connectors.
Strip back a few millimeters of wire on the JST extension and then tin them for soldering. Solder one wire to the driver's output and the second wire to the power rail, which will carry 5V. Solenoids do not have polarity, so it doesn't matter in this case which wire is connected to either soldering point.
Continue this for all of the solenoids.
The process of wiring up the multiplexers to the drivers can be a little tedious. To avoid any major mistakes you can wire up one driver to each multiplexer to make sure that I2C is working and that both driver boards are outputting to the solenoids as expected.
It also helps to have a cat inspect the circuit's progress.
The ItsyBitsy is attached to the 1/4 Perma-Proto with socket headers. Power, ground and I2C signals are run via long wires to the other Perma-Protos through the case's wiring slots at the bottom.
A toggle switch is in-line with the USB power signal from the ItsyBitsy that supplies the ULN2308's. This allows you to have control over the solenoids receiving power in case of a problem.
This particular toggle switch also has an LED at the top that lights up when power is engaged.
- The toggle switch's GND is connected to the ItsyBitsy's GND
- The toggle switch's + pin is connected to the ItsyBitsy's USB pin
- The toggle switch's headlamp pin is connected to the ItsyBitsy's USB pin
With everything wired up, it's time for the final assembly.
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