Eghbal and I made solenoids for our final project! First we designed a board in eagle which contained an N-channel mosfet and a schottky diode and made pads to connect to a previous echo_helo_world board so that we could use the existing ATTiny to control the MOSFET to actuate.

First I had a small problem cutting the board out because inputting the true DPI exported by eagle (500dpi) led to a board that was 2x the size! I just adjusted it to cut with 1000dpi to get the right dimensions. Next I designed a solenoid part in Onshape and printed it on the sindoh. At first I printed it with a hole in the center with the exact dimensions of the metal peice that we wanted to move but I failed to account for the tolerances of the printing and thus had to make a new part with a larger hole.

Next we wrapped these parts in wire for several hundred turns (this is rather imprecise but we wanted to just do a proof of principal that it could work at all since we haven't settled on the weight that we want to move). After wrapping a bit of gorilla glue held everything in place and Eghbal stripped the ends of the solenoid using a soldering iron. We next checked the resistance of the solenoid which was ~30 ohms. Then to make sure that the solenoid worked before attaching it to the boards we simply hooked it up to a 5V power source and manually tested that it could pull our part towards the center (see 2nd gif).

We then built the jumper board and hooked up our solenoid. We drove the solenoid with the ATTiny in an oscillating fashion which is modulated by the button. Next we plan to use several of these to move a series of wooden mallets. We found some springs which will push the mallets up away from the instrument that we wish to play until the solenoid moves down, allowing the spring to move and the mallet to stike the instrument.