Looking for a schematic to drive a small relay.

[Guest]

Hi there, I'm looking for a schematic diagram. The working voltage is 12V DC, when there is about 5VDC at the input of the transistor, the relay is not turn on, if there is approx 0VDC / grounded / less than 1VDC, the transistor will turn on the relay and with at least 1-2 seconds delay off the relay. Thank you. ;D

 

[Alun]

Try this, the relay will turn off when the input goes above about 0.6V.

 

[Guest]

Hi Alun,

Thanks for your reply. Can this circuit add up with the delay turn off function? When the input at the 100K resistor goes above 1V, the circuit will delay 1-2 seconds (adjustable) to turning off the relay. Thanks.

 

[Alun]

Sorry, I missed the last part, what do you mean?

(a) The input goes low and the relay turns on for 1-2 seconds.

or

(b) The input goes low and the relay turns on and remains on for 1-2 seconds after the input goes high.

a or b which is it to be?

ps
You might have to wait until Monday for me to reply as I'm going away for the weakend.

 

[Guest]

Hi Alun,

Thanks for your reply. I prefer the (B). When the input goes low, the relay turns on and when the input goes high, the relay maintain on about 1-2 seconds and then off again.

Thanks.

 

[Alun]

Sorry for the delay - I've just remembered this thread.

Try this.