This week, I wanted to make a board that could drive 3 voice coils. My plan is to make a system with 12 voice coils (self wound eventually). I hope that the boards will be networked, and each will control 3 of the speakers. I drew my schematic in eagle.
The layout was really difficult with a single side. So I introduced more connectors to give me work around room. Another thing I did to make routing easier was to use the following settiings for the mill:
Mods bit width: 0.001”
Milling the traces went find, but it was Milling the outline which caused me trouble. THe 1/32” bit broke halfway through the cut. I think the issue was that the height of the cut was changing as I was cutting, causing the bit to go deeper than it should have. This may be due to the base sacrificial layer not being completely flat.
I finished cutting out the board with an exacto knife and a snapping motion. I then stuffed the board. At first, I coudln’t find the H-bridge chips I had designed for (A4953), but thanks to a tip from the class section, I found them in the inventory.
After full stuffing, I was able to burn the arduino bootloader on the system.
I set up the system to use software serial so I could communicate with it. This is a screenshot of the system communicating on 9600 baud. In order to figure out what pins to use for software serial, I checked the core file for the arduino bootloader to cross-reference the pins.
Halfway through development with the board, I ended up ripping off the icsp and the traces. This may be due to me over-using it or under-soldering it. Kinda frustrating.
I also utilized a 14V power supply and connected arduino headers to it. I did the same for an 8 ohm speaker I found in the inventory.
The code for controlling the speaker using software serial and software pwm. The plan in the future is to use the same timer to control the pwm for 3 speakers.
I went back to redesign the system using a single mosfet instead of an h-bridge for the speaker. Thanks to a tip from Neil, I am going to implement it using a voice coil, a magnet, and a spring. The mosfet will only be able to push the speaker in one direction, but the speaker will be able to return it. Since a mosfet will only require 1 pin, It should increase the number of speakers I can control with the attiny to 12. Pretty dope.