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Skenny

wrote:
On Jul 29, 7:26 pm, "Stephen J. Rush" wrote:

On Sat, 28 Jul 2007 21:08:09 -0400, Broderick Crawford wrote:

What't the difference between a retriggerable one shot and a regular
relay? Isn't that the same thing?

The basic one-shot will ignore a trigger pulse that arrives during its
'on' period. A retriggerable one-shot will stay 'on' for as long as
triggers arrive before the circuit reverts to the 'off' state. One of the
uses of the retriggerable version is as a watchdog timer, to raise an
alarm if an expected event doesn't happen on time.

Hi

This sounds like exactly the thing I need. I read up on relays on
internet but still I dont' find any that has an 'ON period'. Can you
explain more or tell me how to search for them.

What I want to do is as following. I want a small voltage (A) to
trigger an event (B). The B process must run for longer than the A
signal.

E.g you briefly press a button and a motor starts turning. Once a
complete revolution is done, it stops and you can press the button
again to start the process.

Couldnt you just use a regular relay, have it latch until a limit switch
is activated by the motor's revolution?
The limit switch is open while the motor is "at home position".
The button "shorts out" the limit switch, turning on the relay. The
limit closes when motor turns, holding relay on until limit opens again
at home position.
You might have to hold the button until the limit closes, but this could
be overcome by using another relay that "latches on".
I can draw you a simple diagram, if you are interested.
Of course, if the button and limit switch can handle the motor's
current, you probably wouldnt even need a relay.