Hi,

I am looking for help on making a simple switching/pulse project.

This device needs to work of 12v dc.

Right now I have relays doing the switching but I have many catch 22's with this and I am thinking a IC 555 timer maybe needed here.

Basically what I need is a setup where when 12v dc is applied a pulse is sent to "short" a power button. At this time I have done this by using a 12v relay with a 5v relay. When I apply 12v to the device it trips the relay and shorts the connection after that the device I am turning on supplies 5v to a 5v relay that releases the 12v relay so that the 12v relay will not hold the "short" to the switch as I need a simple "quick" pulse to complete the switch circuit.

This device simply replaces the need to press the momentary button manually.

The 1st problem with my current setup is that I also need it to "short" the switch when 12v is disconnected from the device.

The 2nd problem I am having is when 12v is applied I need the pulse to be delayed, say for 5seconds (A variable pod would be great so that the delay timing could be adjusted from 1-15 or maybe up to 30 seconds)

here is a link to my current schematic.

 

Hmm... maybe it would be better to use a NE555 timer chip than two relays though you can delay a relay by using a transistor/ capacitor/resistor combination. If you really enjoy electronics then I would suggest you learn to use a small PIC micro.

 

On second thoughts, I have just had a look at your page and have seen what the project is for, stick with your relay.....