On 9/6/2013 8:59 PM, 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
Attached is admittedly quick-and-dirty, but it's ever-so-simple; no 555
timer involved. Most any garden-variety N-channel MOSFET with Vgs(on) ~=
4V will work for Q1, but performance may vary from FET to FET. Depending
on the Vgs(on) of the FET you select, you may want to fiddle with the
value of R1 to get as close to 5 seconds as you desire.
Change the value of R2 to increase or decrease the forward current of
the LED and resulting brightness.