help needed with pulsing a latched realay

[digitecks]

hey im new on here but , i have dabbled with electronics over the years,

my question is im wanting to give a relay/device a constant 12v + or - dose not matter about the polarity , but the out put from relay/device to pulse once when a constant power is added , and to pulse once when power is removed

not found any devices or relays as yet that will do this so any help most gratfull

 

[duke37]

More information woul be helpful (I am always saying that).

One way would be to connect a capacitor to the relay contact so that a pulse is generated when the relay pulls in. Another capacitor connected to the back contact would give another pulse when the relay drops out. These pulses could be added with two diodes to provide an output signal.

 

[Harald Kapp]

Alternatively, you could use a ploarized relay and add a sufficiently large capacitor in series with the relay coil.
When applying a control signal to the relay coil the charging current of the capacitor will trigger the relay. When the capacitor is charged, the current will drop to zero and the relay will fall back in its idle position.
When you remove the power, you have to make sure that not only power is removed but that the circuit of relay and capacitor is closed. My schematic uses a SPDT switch for this purpose. The discharge current of the capacitor will then trigger the relay.

Harald