Some Electrical Questions

**Kayos Frawg** · 04-15-2004, 10:45 PM

I've been hanging around the boards for a while, and I'm finally going to be able to start my carputer project. I have a couple of questions about some electrical components though.

I wanted to add a little something to my alarm system. When it gets tripped I want it to stop the car from starting. I think this can be done by disabling a wire that runs to the ignition, so this way even if they open up the steering column and put the two wires together the car wont turn over. I was thinking have a relay connected to the alarm, so that it is triggered whenever the alarm is. Then have that running to something on the (12v?) line that is usually in the "on" position allowing current through, and when tripped by the relay, switches "off" and requires a manual reset to allow current back through the line.

I don't know if what I was thinking is possible, but I think that it is. The main thing I'm fumbling with is what to put on the line that will disable the turnover.

The next thing is a relay controller. I found this and I'm not sure its what I want. It gives its rating in AC, so does that mean that it cannot work with DC? If not has anyone found a USB relay controller that does work with DC?

**arkadiyp** · 04-15-2004, 10:56 PM

What you have described is exactly how alarms work in general, so what are you trying to build?!?

**starfox** · 04-16-2004, 07:48 AM

Relay ratings are usually in AC because relays often switch AC

As long as your DC voltage is less than the RMS of the AC you should be fine (max AC voltage multiplied by square root of 2).

Watch the maximum current rating though, that's usually the limiting factor. The relay controller you've posted above is only 10A, it won't be suitable for some car circuits.

**kiltjim** · 04-16-2004, 03:56 PM

Check with your security system company. They might have a starter cutoff built just for that purpose.

As for a relay board use this one.

Someone on the board has posted code to let you control it, both for Pre-XP, and XP.