More KiCad

Top Layer

I am becoming more skilled with KiCad and cant seem to stop laying out boards. I designed and purchased this one last night for testing out my solenoids on the test playfield. I am no longer willing to navigate through spaghetti wiring and loose breadboard connections while working. It's so frustrating trying to design something without being able to rely on the robustness of a previously working design. It is always good practice to work on one thing until it works every time without failure, and only then move on to something else. I'm hoping this board will do just that. Each one can independently control 4 solenoids with an ATTiny85, and be mounted on the bottom of the test playfield using the four 6-32 mounting holes in the corner. I can then route the power rails to screw terminals, making disconnecting the power from the playfield quite simple.

Bottom Layer

Silk Screen and Edge Cuts

This is the schematic I drew up originally of the solenoid driver. the 40V is isolated from the logic through an opto. because of the way I have done this the logic to turn the solenoid on is backwards. So when my output is high the solenoid is deenergized and when the output is low the solenoid energizes the problem with this logic is that there is a high probability that the solenoid will stay energized and burn out. So my design tries to counter act this by using a PNP transistor to invert the signal before entering the circuit. This method still doesn't fix the underlying problem though. Keeping the solenoids turned off requires the use of my 5v supply. In the event of my 5v supply failing, every solenoid would fire and blow a fuse, burn out a coil, or worse. So my new design uses an output of the MCU to fire a relay which switches on and off the 40V rail to the coils. Now my coils wont have power until I output a signal. A signal that is not available unless my voltage source is on.

New Solenoid Driver Portion