Electronic Guru help required.

[Brax]

A friend of mine has a ham radio in his car. He doesn't want it on when he first starts his car to prevent any surges or electronic "crackle".

He wants a circuit that will run off the ignition power and have a switch inline. The trick is that when he turns off the key he wants the power to shut off (easy) but when he turns it back on he DOESN'T want it to come back on until he touches the switch again.

I can't quite get my head around this one.. I'm thinking about a momentry contact switch and maybe even a relay would be required but I can't quite figure out how it would work.

Maybe a filter of some kind could also work? Could it be easily constructed instead of purchased? (he's cheap! ) Honestly, I think he'd prefer this switched circuit instead of a filter though. Not only is he cheap, he's paranoid.  

Is antone here smart enough to come up with the switch solution?  

[paigeoliver]

I can't quite get my head around why he just doesn't wait until after he starts his car to turn it on?

[Tiger-Heli]

A friend of mine has a ham radio in his car. He doesn't want it on when he first starts his car to prevent any surges or electronic "crackle".

He wants a circuit that will run off the ignition power and have a switch inline. The trick is that when he turns off the key he wants the power to shut off (easy) but when he turns it back on he DOESN'T want it to come back on until he touches the switch again.

I can't quite get my head around this one.. I'm thinking about a momentry contact switch and maybe even a relay would be required but I can't quite figure out how it would work.

Paige is right, unless I'm missing something.  Edit - I found the problem.

What I was thinking - If he wants to touch the switch to turn on the radio, then all he needs is a rocker or toggle switch wired to a circuit that is only hot with the engine running (say the heater or sth).   This will allow him to press the switch to turn it on, and it will automatically turn off when the car goes off.  PROBLEM: With this circuit, unless he flips the switch back, the radio will come on as soon as the car is re-started.

What you need is a delay timer circuit, in front of the switch.  I don't know how to wire one, though, sorry.

[Radical]

Try asking over at http://www.eham.net/forums.  They usually are very helpful.

By the way, some radios have a setting as to whether or not it will come back on after losing power.  Depending on how old the radio is you might want to check that.

[BobA]

This tdr should do the job.  There are many different units available for different loads from electroinics supply shops.http://www.kussmaul.com/091-100-012.html

BobA

[Brax]

That should work thanks!

Now I just have to figure out how to interface this to my comp..... hehe