Electronic Wizards

[teenix]

Thanks for the answers :-)

I tried a simple N FET buffer (2N7000). It worked at low frequency but not at 200 odd KHz, although breadboarded with flying leads probably not good. I was a bit worried about the gate switching currents on the clock source. It is hard to test different parts due to high postage rates to source them. I tried a few diode types but slow signal response and also faster Schottky but passed negative voltage

I actually posted this to an electronics Forum before thinking that there are some very smart people here so as it is calculator related in a way, maybe worth posting here.

I got this circuit from someone last night with scope traces showing that it works, so it is worth a try.

Another choice that came up was 3 resistors connected as a voltage summer, (superposition), but may load the clock source.

Space on a circuit board is very limited so the smaller the circuit the better, although I can sandwich two boards if that is required.

cheers

Tony