> > Ok - all detector inputs come through a bunch of OR gates (small signal
> > diodes) to ONE input.

I've had some trouble with diode-ORing clock pulses and had to stretch
them to get through the diodes. Could it be that the capacitance of the
diodes (1N914/1N4148) is too high for pulses in the region of 1us as
you'd find in a typical bsf nop bcf operation ?

> > One output pin clocks through cascaded decade counters, each
> > output of which fires up an LED in your light barriers one-at-a-time.
> > The third output resets the counters for guaranteed synchronisation
>  > at the start of each cycle

If you're thinking of something like a 4017 (active high Reset), connect
a resistor, say 10k between Clk and Reset, and a cap of around 100n
from Reset to 0V. A short pulse to Clk will get through, but will be too
short to charge the cap on Reset through the 10k. Lengthen the pulse
enough to charge the cap to bring Reset high and you've got a one-
wire control for Clk and Reset

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