TT064 Mitra Prescaler

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).

No, TT064B changed the input to a PulseShaper.  See comments following

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.

Power is through a 12V wall-wart.

The reason for the divide-by-two is that it makes a cheap pulse stretcher.  The resulting pulse stream is usually fat enough to be processed by low-speed counters.

Marked-up schematic for ToprCmp2FPGA:

FPGA is simply a pair of toggle flip-fops.  Put schematic here:

ToprDout2 schematic (no changes):

The baseboard is a TipTop1590G with only the 5V regulator installed:

TT064B pics: