So here is the setup: I have an array of 12 tiny solenoid valves mounted over a 36" conveyor belt that is being driven by a 1/30 HP, 90V motor (and is located about 8 inches from the valves). I have a chip (actually an FPGA) that outputs 2.5V for hi and 0V for lo, and is driving 12 NPN transistors through 500 ohm resistors. The solenoids are hooked up across 5V and the transistor, with a protection diode in place, just like on page 23 of the "interfacing circuits" PDF. When the motor gets above a certain speed though, the valves all start randomly firing, and I can see that the outputs of my chip are no longer at 0V (jump around from -.6V to 2.5V somewhat randomly). The FPGA is powered from a 9V wall-wart type power supply with an onboard 2.5V and 5V regulator, and the valves are powered from a 5V lab PSU, while the motor is powered by a 90V rail-mount PSU. It's somehow interfering, but I don't understand how, so any advice would be appreciated!
p.s. There is a picaxe feeding data to this, so it's not completely off-topic!
p.s. There is a picaxe feeding data to this, so it's not completely off-topic!