On Mon, 12 Apr 2010 17:32:47 -0500, "Dave" wrote:


"Hammy" wrote in message
.. .
On Mon, 12 Apr 2010 15:52:09 -0500, "Dave" wrote:




Okaaay. Thanks Fred. Just out of curiousity, what made you think of
this?
Is there some dark secret about the 555 that I have somehow missed?

Many thanks. Off to the workbench...

Dave


Hi Dave

Go here and read the part "Selecting External Components". You'll find
the answer to your ?

http://www.williamson-labs.com/555_apps.htm

Hey Hammy. Checked it out, but it didn't really tell me anything I didnt
already know. If the problem were simply the signal being out of expected
parameters, or the resistors/cap being high or low in value, I would still
have some kind of signal to work with. Instead pin 3, which is the output,
goes to ground as soon as the power is turned on. As I told Fred I think I
have to have something hooked up wrong. Just have to figure out what it
is...

Thanks anyway.

Dave

Then you missed the part where it says "there are certain minimum
values of resistors......" and "it is recommended a 5kohm resistor be
the min for RA....."

You may have already damaged the timer. The timer charge/discharge is
current limited but it still may be damaged depending how long it was
running with those low resistor values.

Usually you would select as a high a value resistors as possible and a
low nF (nano farad) capacitor.

You might want to try it without your load ,first get the timer
working into a resitive load , then attach your JFET.