Re: Looking for a Low Cost On Delay Timer

[John Sowden <jsowden@xxxxxxxxxxxxxxxxxx>]

On 08/21/2013 10:39 AM, 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.
>
> Thanks,
>
>
> Bob
>
Get a sensitive relay (coil 1k ohms or so), put about a 3ooo uf
capacitor across the coil, apply 12 volts to the coil, the relay will
hold closed while the cap is discharging into the coil.  Use the n/o
contacts to do what you want.


John Sowden
American Sentry Systems, Inc.
San Francisco Bay Area