9/27/2014 – Incandescent driver board tested

Here is a picture of the populated incandescent driver card:


The picture shows the MOSFETs in the correct orientation, and all the connectors placed the correct way.    The four and two pin connector on the right side should be a six pin connector, but I made due with what I had for the first card.  Same with the two connectors on the top right.

Spent a couple hours today and tested out the incandescent driver board.  To test the board, I built another board to use a computer’s parallel port to drive the SPI signals, and an old PC power supply to prove the 12V and 5V.  The picture below shows the parallel port to incandescent interface on the top right corner, and the incandescent driver tester on the bottom.  I haven’t had a chance to cut the two boards apart yet.


The converter board at the top has spade terminals for the 12V, 5V and ground from the power supply.  It also has the six pin connector that gets connect to the incandescent driver.  I cut a DB25 cable in half and used D0-D2 from the parallel printer port drive MOSI, SCLK, and SS*.

The test board is at the bottom of the picture.  Each pin of the four two pin connectors drives an incandescent lamp.  The incandescent driver board can be used as either a high side switch or a low side switch.  All of the playfields I have looked at in depth use a wire braid to return the GI lighting current back to the power supply.  That means that you need to provide a high side switch (i.e. cut switch the voltage on and off instead of switching the connection to ground on an off).  Since it is a high side switch, and I’m using an N-channel FET, to turn the FET on and off, a voltage is needed which is VLED + Vthreshold for the FET.  The threshold voltage for the BS-170 is 3.0V max, and most pinballs use 6.3VDC, so about 10V is needed to turn on the FET.  The power supplies provide 12V, so that should work perfectly.

So trying to lay out the board quickly, I messed up one signal.  The G* signal on the STPIC6D595 needs to be grounded instead of pulled up.  That’s a simple cut of a trace and add a wire on the back of the board.  The mistake is disappointing, but it is easy to fix.

Since the incandescent driver boards are being used as high side switches, the spade terminals on the card are connected to VLED.  I bought a couple of buck converters to change the voltage from 12V to 6 or 7V to drive the LEDs.  That should make them look a lot less anemic.  Each pin of the two pin connectors go to a light bulb and provide the power to turn it on and off.

Next step is moving towards the Pi.  My laptop doesn’t have a real parallel port, so now I can’t easily run feature lights and the serial interface off the laptop, so it is time to start getting stuff working on the Pi.  That will reduce the amount of voltage conversions that I need to do.  I will end up using a voltage converter chip to move the 3.3V Pi signals to 5V for the old driver cards (won’t be necessary with the next generation of cards), and then the conversion to convert the SPI bus signals to 5V.  I will put down a second chip to convert the 5V from the Tx output from the input/solenoid driver boards back down to 3.3V.

I have to build a bunch of boards for Cactus Jack, but I’m not sure how he is going to drive them.  That might require a few emails to figure out how he wants to drive that stuff.

Oh yeah, here is  a link to the video of the incandescent driver running the test fixture.  A 200ms sleep was tossed in so that it didn’t blink too rapidly to film.  Running at full speed, the flashing was so fast my eyes couldn’t detect it.


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