optocoupler for 5vdc signal, and 14vdc (360ma) load

[Mad Professor]

I am looking for some help and advice on what component(s) I need to do the following task.

I have been helping a friend retrofit their diesel backup generator, The generator it's self is fine, but the diesel one day decided that it's internals would look much better on the outside.

My friend was going to scrap the whole generator, but one say I jokingly said how about retrofitting the generator with a automotive common rail turbo diesel engine.

Well after a lot of head scratching, cursing, etc, the donor engine is now in, fitted, and running.

Now here is where I am looking for some help and advice.

I need to be able to turn on a pneumatic 3 way valve when the engine is at idle.

The coil of the pneumatic valve is 40R and the max voltage it should ever see is 14.4v so we are only looking 360ma.

I know the simplest approach would be to just add a microswitch to the throttle.

But I never seem to want to do things the simplest way.

The throttle has both a idle switch and a potentiometer (See Attachment).

So this got me thinking if I could use the OEM throttle to control the pneumatic valve.

1) Idle Switch output, 0v at idle (switch closed), 5v off idle (switch opened), must have pull up resistor in the ecu.
2) 0v.
3) 5v.
4) Potentiometer output

My 1st problem I found is that the 0v pin is not the same as battery ground, so the ouputs from the ECU must be isolated.

At this point in time the only thing that pops into my mind that I can use is a optocoupler of some kind.

I want to try and keep the component(s) used to a minimum as possible.

The next problem, and probley the most limiting of all, is that I don't want to have to wait, and or place a big order with say RS, Farnel, etc, just to get a few component(s), So this is really limiting me to eBay or dare I say it Maplin Electronics.

Please me let know your thoughts on this.

Thanks for your time.

Best Regards.

[tggzzz]

The next problem, and probley the most limiting of all, is that I don't want to have to wait, and or place a big order with say RS, Farnel, etc, just to get a few component(s), So this is really limiting me to eBay or dare I say it Maplin Electronics.

They don't have to be big orders, but you would pay some postage (which can be compared with the cost of a trip to Maplins).

If you have an RS counter shop nearby, they do free next day delivery to their counter shops.

[Paul Moir]

The thing about interfacing with unknown electronics is you don't really know what kind of current will be available to you.  You might not have enough on that 5v to power the LED in an optocoupler.

If you measured the 5v on the switch to ground, I would tap that off with a logic level (5v to turn fully on) mosfet.  The mosfet could drive a relay and you could use the NC contacts to drive your valve.

OTOH, this will allow the valve to be on when the ECU is off.  That may be a problem? 

[cpt.charlie]

You could use an optoisolator driving a mosfet, if the current of the MCU is a problem, maybe an opamp as buffer may work.