On Sat, 07 Sep 2013 13:35:25 -0700, Jim Thompson
wrote:
On 07 Sep 2013 20:21:35 GMT, Jim Mueller wrote:
On Fri, 06 Sep 2013 20:59:46 -0700, Guv Bob wrote:
"Jim Mueller" wrote in message
b.com...
On Fri, 06 Sep 2013 09:57:57 -0700, Guv Bob wrote:
snip
Thanks Jim. I have no experience with 555 timers. Where would I
find a basic circuit for this application using a 555?
Here's a data sheet: http://www.ti.com/lit/ds/symlink/lm555.pdf. It
has a number of generic circuits. What you want is a monostable
circuit. It can be set up to trigger from power-on or from a separate
signal. Can you modify the example circuit yourself or do you need
help?
--
Jim Mueller
To get my real email address, replace wrongname with dadoheadman.
Then replace nospam with fastmail. Lastly, replace com with us.
Thanks, Jim, that's a big help. I'm afraid I do need more help.
Someone also mentioned needing a diode. I'm pretty lost at the
component level.
If it helps, the application is to energize a small LED for approx 5
seconds when 12VDC is applied to the input. After 5 seconds the LED
should go off even though 12VDC is still on the input.
I don't have the LED current draw, but it's very small - probably on the
order of 10ma.
Many thanks for this help!
Bob
The circuit in the link from Jim Thompson, http://www.analog-
innovations.com/SED/5-Second_Timer.pdf, turns the LED on after 5 seconds
which is the opposite of what you want. To reverse this (one way of
several) is to disconnect R1 from +12V and connect it to pin 3 of the
555. Then, the cathode of the LED is disconnected from pin 3 and
connected to ground. The 555 is somewhat unique for an older part in
that it can source a substantial current as well as sink.
Huh?
The way I read Bob's OP...
http://img839.imageshack.us/img839/4650/uh3.gif
the relay closes after 5 seconds, activating the LED.
Did I miss a post reversing that?
---
Here's his original post:
"Names can be confusing, so here's what I'm doing....
http://img43.imageshack.us/img43/7434/wvm.gif
When 12VDC is applied to the input, I need a 12VDC output for 5
seconds. Then output will go back off and stay off until the input
goes to zero. Then cycle starts again."
--
JF