Processor-less instrument consisting of a ToprCmp2FPGA dual high-speed comparator with an FPGA configured as a divide-by-2 counter. Output is a ToprDout2 board, a simple 5V digital driver with 50 Ohms of source impedance.
TT064B is an almost-identical copy for the Doyle group. The only difference is that the input threshold range is changed from (+/-1V) to (0 to -1V).
Comparator thresholds are adjustable from -1V to +1V with the blue trimpots. You can monitor the threshold by putting a voltmeter on one of the MON pins. You can see white lines connecting the MON pins to their respective input channels. For the voltmeter's ground, use pretty much any exposed metal – BNC shields, screw holes, etc.
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