I'm afraid it's difficult to read because I only cobbled it together to get a PCB layout for OSHPark. I'll try to walk you through it.
Missing completely from the schematic are 6 automotive 12v relays. Pad power +12v goes to the igniter then to one tab on the relay switch and the connectors on the left (J1). The other tab on the relay is switched to pad power -. When there is continuity through the igniter, J1-1 (for the first pad) will be high, then to the pn2222 transistor which turns on the pad continuity led (cont1-1 connector), and also turns on the led in the ps2502 opto-isolator.
The connector across the top goes through the cat5 back to the controller circuit. J2-1 is +12 from the controller (and powers the control side of the relay), J2-2 is - from the controller, and J2-3 is the control signal for pad 1, etc. The eventual plan here is to have the controller power tap off to switch some alarm circuit like a buzzer or strobe so when it is selected from the controller, people know it's hot.
J2-3 is the control & continuity signal for pad 1. When there is continuity, there is a completed circuit from +12 through a voltage divider to J2-3. J2-3 is then presented with about 7v. When J2-3 is pulled to ground, the MIC4467 (MIC1_1) gate will trigger +12 to the RLY1-2 connector (which is of course connected to the coil of pad 1's relay).
The MIC4467/8/9 is a pretty neat chip. It's basically a CMOS buffered MOSFET. The MIC4467 used here has a CMOS inverter on it (hence why it's drawn like that). Since it's CMOS it has a high logic threshold and allows an intermediate voltage state to be used to signal continuity to the controller.
What's completely missing here is the controller circuit. I'm using a ULN2004 darlington inverter to drive the continuity lamps (LEDs) at the controller, and simple interlock and switch to ground to control the launch.
I have built a single channel version of this controller to test the circuit out and it seems to work like a champ. I'm struggling to pull the trigger on ordering boards from OSHPark because, well, I'm a wimp and think I might have something wrong.
Kevin
View attachment relay4.pdf