"Dave" wrote in message
netamerica...
"hamilton" wrote in message
...
On 4/12/2010 4:29 PM, Dave wrote:
"Fred Bartoli""" wrote in message
...
Dave a écrit :
Building the attached schematic, only I have no signal output on pin 3
of
the 555. My calculations tell me it should be a 10.2 KHz squarewave,
but - nothing. When power is applied, it goes to ground, and I have
checked and rechecked all my connections. Somebody please tell me
what I
am doing wrong. I used the same setup for a transistor tester, and it
worked fine. Keep thinking something has failed to make contact with
the
solder applied to it, but that doesn't seem to be the trouble. I
guess
I'm asking if this *looks* right, cause that would mean I do have a
wiring error. Or is there something here I don't know about the 555?
Pin 3 should have a square wave on it, even if it is not connected to
anything but a scope, right?
Thanks,
Dave
Change R1&R2 to 47K and the 1uF cap to 1nF.
--
Thanks,
Fred
Hey Fred,
I didn't have a 1000 uF cap, or anything reasonably close, so went with
a
10uF tantalum cap and the same 47 ohm resistors, figuring I would get a
1KHz
signal but that was okay. Problem is, the same problem persists. When
the
power comes on pin 3 of the 555 goes to ground. I have to be wiring it
wrong, is all I can figure. If it was configured properly, I should have
some type of signal on pin 3. Will look into it some more...
Thanks for the idea on changing the values.
Dave
Dave,
I think everyone has been trying to tell you that your 47 ohm and 1uf
parts are just wrong. (but they are more polite)
Yes, I see that you "figured" that your numbers should work. But it does
not. You said so yourself.
I have no clue where 1000uf came from.
1nf = .001uf = 1000pf
For future reference: http://www.justradios.com/uFnFpF.html
hamilton
PS: do you have a scope ??
AAaaaah. Crap. Well, I said I was ignorant. 
My apologies. And I
guess I did miss the part about 5K being the min for RA. Will have to go
back and look at that again, more slowly.
And I have plenty of .001uF disks. Damn. I'm sleep deprived right now,
and when I let that happen I get stupid.
Many thanks for the up front and plain-spoken answer. I frequently miss
hints. (Ask the wife.)
And yes, I have a scope. It's a 100MHz Tektronix (sp?). Can't remember
the model # but it's a rugged, militarized version of an already reliable
model, as I understand it.
'Preciate the help...
Dave
Back to the workbench.
Okay, I went back looking for what I obviously missed. And I did
*completely* miss that section. shaking head Thanks again, Hammy. And
now I know not to use ceramic disks for the timing cap. Fortunately I also
have plenty of silver mica caps, which is one of the alternatives that
article recommends. And I am sure I have damaged the 555 chip. But I have
another. Maybe this time I'll do it right.
I'm learning, slowly.
Many thanks,
Dave