I'm working on a pinball project so I trying to build an 8x8 lamp matrix to drive the 6.3V #44 lamps used in pinball machines.
I've seen some discussion on driving larger LEDs but 6.3V lamps are special in that they are high current and the CPU needs to drive them at variable rates to allow for strobing and/or flashing effects, so in pinball machines the supply voltage is +18VDC. In my case I am going to try driving them at 12V since I'm using a switching power supply for testing.
What I've done is essentially duplicated the Williams WPC-95 design for the lamp matrix but removed a few bits like the current limiting logic to make as simple a matrix as possible. I've attached a copy of that design.
Unfortunately I am a complete newbie to electronic design - I can read a schematic basically but, for example, I'm not sure why some of the resistors are there or of their values. Also, I had to replace the original TIP102/107 pairs with TIP122/125 because Eagle doesn't have libraries for those transistors. I'm hoping someone is willing to look at what I've come up with and can offer suggestions on the design.
For reference, I believe the WPC-95 design is ground sink, in that a column is activated and the rows are scanned, connecting the TIP102 to ground and thus lighting the bulb.
I'm not married to this design, but I figured starting with a known working example made sense. Any help appreciated!
lamp-matrix.sch (199 KB)
