"George Herold" wrote in message ...
On Wednesday, August 21, 2013 7:46:13 PM UTC-4, Guv Bob wrote:
John Fields" wrote in message ...
On Wed, 21 Aug 2013 10:30:46 -0700, "Guv Bob"
wrote:
"John Fields" wrote in message ...
On Tue, 20 Aug 2013 14:12:28 -0700, "Guv Bob"
wrote:
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.
Current for both legs is in the 10-50ma range.
A simple on-delay timer would work but I'm having trouble finding one with NC contacts. Tons of stuff $100+, but for this application, it has to be under $20.
---
For way under $20, this'll work, and if you need NC contacts, all
you'll have to do is put either a solid state relay or a mechanical
relay with a catch diode across the LED.
Thanks John, I'm not following you. Can you sketch the circuit?
---
Sure.
View with a fixed-pitch font like Courier New:
GND-\ - +12
O-----+----+---+---+------+-----+-------+ +--------NO
| | | | | | | | | O--C
| | | | | [680] |K | O- \--NC
|K | | | | | [1N4148] [COIL]- - - -\
[1N4148][7M5][100K]| [10K] [LED] | |
| |Rt | | | |K | |
| | | | | +-----+-------+
| | | | | |
+-----+----|--|-\ | C
| | | -+----B 2N3904
|Ct +--|+/U1 E Q1
[1µF] | | |
| [100K]| |
| | | |
GND--------+----+---+----------+
U1 is any comparator with an input resistance which won't swamp Rt,
and an open-collector output (or an output with a weak pullup to Vcc)
which can sink a few mA without letting Q1 go out of saturation.
So, what's your application?
--
JF
Thanks again! Would this work?
NTE955M Timer, (555 Type), 200 mA Iout, CMOS 8 DIP 1.20
http://www.alliedelec.com/search/pro...x?sku=70215850
I was going to say this sounded like a perfect fit for a 555 timer.
(So what's the best RC combo to get 5 seconds from a 555?)
George H.
I used to know all that stuff by heart, but I've been swapping modules too long. This not the usual rush job, so it's a nice change to be able to spend some time on it. Now I'm off to re-learn all the RC stuff.