Mike's Project Tracker

Multimeters can give false voltage readings if they have a low battery even without the low battery warning. I mounted the components for the voltage regulator for the MOSFET Driver Board in order to test the regulator by itself.  The regulator drops the voltage from the 48V solenoid power supply to between 1.2V to 30V.  The 30V upper limit was set because the D223 optocouplers cannot handle more than 30V so it is pretty important that this works. MOSFET Driver Board with Linear Regulator Mounted The regulator pot was used to set the voltage output to 12V but the 12V started to drift high, just tenths of a volt at a time.  I thought that my regulator just needed to come to steady state as my set resistors were heating up and thereby causing the voltage to drift.  Also, the 48V power supply is one of those cheap ones off eBay or Amazon so I did not trust it very much.  After a few minutes, the voltage was still going up and I tested the voltage supply ...

Red PCBs do look sharp.  The MOSFET Driver Board PCBs came in and overall they turned out well.  Compared to previous boards I have ordered from Seeedstudio, the tin on the pads is a bit uneven and the inkjet for the silkscreen must have got gummed up.  You can see that the silkscreen is a bit messed on the white rectangle I left as a space to write on.  Small gripes for hobby PCBs and overall I'm quite happy how they turned out. MOSFET Driver Board PCB

Optocouplers can be used on the high side without issue. Optocouplers let us isolate two separate power systems.  In the case of my pinball project, I am using a computer PSU to power the logic, lights, and lower voltage items like motors etc; and I am using a somewhat suspect 48V power supply for the solenoids.  To keep these systems separated, I used optocouplers on my mosfet driver board. When designing the board, I was concerned that my transistor like optocouplers would not perform on the high side of the mosfet gate.  You cannot easily use a NPN transitor on the high side (Emitter Load).  You would normally use a PNP transistor.  The test circuit in the data sheet also showed the optocoupler in a low-side (Collector Load) configuration.  Why did I not use a high-side configuration?  Well, say if something went wrong with my optocoupler, I want my mosfets to default to the off position, ie. ground the gate.  With a high-side configurat...

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 ...

Last November, I fried my 'lab power supply' that I made from a computer PSU.  I was testing my solenoids and the stress was just too much for the PSU.  The mistake I made was rapidly turning on and off my solenoid which likely resulted in voltage transients (spikes).  Since the PSU does have a current limiter, it was likely the constant voltage spikes that caused the damage.  There are various methods to suppress voltage transients such as by-pass capacitors and zener diodes.  In particular solenoids and other inductive loads experience these voltage spikes, hence my no longer functioning bench power supply. ATX Breakout Board I could have just rebuilt the same power supply by adding binding posts etc to the PSU housing but after searching the internet an ATX power supply breakout board seemed a popular option.  The main advantage compared to my old power supply was the addition of fuses on the outputs.  The extra safety this provides is perf...