Hi guys,

I am trying to use the 555 configured as an astable, with a variable Ra =
(the resistance between 7 & 8), and measure the output pulsewidth (the =
ON time) on a 16F84.

The results I get pretty much match what the specs. of the 555 would =
expect, but there is a strange problem. The circuit is so unstable, if I =
just touch either pin 6, or 7, the readings go haywire. Same happens if =
I solder a long wire to place the resistance remotely as a sensor. I =
tried a bypass capacitor, a shielded wire for the remote resistance etc. =
but nothing seems to work.=20

My power supply, incidentally, is pretty well regulated, and I dont =
think I can suspect that.

Besides this problem the circuit works so well, I am reluctant to give =
it up in favour of some other scheme.

Any hints and advice would be highly appreciated.=20

Incidentally, I tried a 7555, the CMOS version as well; same results.

Regards,

Anand

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