Here is my schematic so far for my solenoid driver board. The PWM control took up too much space to include on the board due to the limitations of EagleCad's freeware. Each control circuit has two inputs, one for the trigger and one for the PWM power control. I might add in a way to disable the single pulse generator so that you can just trigger it on or off if there is room on the board. However, I can only think of a few instances that would require it as most solenoids will burn out if left on too long. I will post the EagleCad files including the board layout when I am finished.
Final version? I hope so. I have gone back and redesigned my solenoid driver board several times. In previous versions I attempted to offload some of the logic from the microcontroller. For example, I used a Schmitt-Trigger [74HC14] with an RC network to provide a single pulse to the solenoid. Also, I added in a PWM signal to set the average voltage 'seen' by the solenoid. This worked but was very limiting to have the pulse length hardwired in and it was difficult to adjust without more expensive precision potentiometers. I chose to simplify my circuit to make it a general MOSFET driver for flexibility. Since I have more than enough space inside my pinball cabinet, it was not a problem to have the extra boards. The boards were designed to have 4-channels since by default I would get a minimum of 10 boards for the same price from Seedstudio. Also, the cheapest board option was restricted to 10cm x 10cm otherwise the price balloons ...
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