Michael Karas wrote:
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You should also re-evaluate the use of the HC109 flipflop in the configuration you have chosen. As it is now the flipflop can toggle at will whenever there is a clock on its input (unless the microcontroller is holding down on the clear ball).

It is supposed to toggle as soon as it receives a clock. The "clock" signal on the chip is a sync signal that goes high at the start of a new sample.

When the circuit is inactive the controller holds down the clear ball, which keeps the 163 counter on zero all the time (the flip-flop controls the LOAD' input of the 163). Then when the circuit has to be "started" the clear ball it set high, and the 163 starts counting as soon as the sync signal has set the flip-flop.

Once again, since it comes through a cable via the header, the 'HC109 clock should at least be buffered via a schmidt trigger type gate or buffer. Noise on this line could cause the HC109 to toggle inadvertantly and then cause the HC163 to clear before its time.

Are there any non-inverting schmitt triggers available, or should I use two HC14s on each signal?

I do not understand the exact usage of this FF but maybe a more appropriate configuration would be a D type with the D tied high and then it clocks on only only once and the microcontroller takes care of starting the next cycle via the clear ball.

Wouldn't that work exactly as the present circuit, or am I missing something? The reason I use the HC109 is also that I need an S-R flip-flop in another part of the circuit, so both halves of the chip are used.

Best regards,

Mikkel C. Simonsen