SparkFun Forums

[smp4488]

I was looking at the power adapter for the relay board and it needs 5V. If im putting this in my car i need to regulate the 12V to 5V. I looked at the 5V regulator, will that work. Also, what is the common line for?

[Encryptic]

I was looking at the power adapter for the relay board and it needs 5V. If im putting this in my car i need to regulate the 12V to 5V. I looked at the 5V regulator, will that work. Also, what is the common line for?

Common is another term for ground.

[smp4488]

Will it work for my 12V line in?

[Encryptic]

Something I just noticed, is it appears that the board actually requires a 12v source, according to the schematic it has a regulator.

Yes, the ground from the 12V source will work, BUT you should check to make sure that it's a clean 12V and that it's really 12v. An efficient regulator may be a good idea, just for safety.

[smp4488]

Where on the schematic does it show the 12V in?

[Encryptic]

Where on the schematic does it show the 12V in?

Upper left shows PWR comming in, going to a +12V signal, and then going into a +5V regulator.

[smp4488]

Ahh got it. I might order the parts tonight but im still a little weary weather or not i can program it. I don't want to buy all these parts then not be able to do anything with it.

[Encryptic]

Ahh got it. I might order the parts tonight but im still a little weary weather or not i can program it. I don't want to buy all these parts then not be able to do anything with it.

I'd hold on, and wait until someone who knows the AVR microcontrollers better. Also, upon some examination at the schematic, the 12.6v connection might be fine without any regulation, it already has a capacitor there on the schematic and appears to only go to the relays.

[daemondust]

From the description, the relays should take up to 120v, but it isn't safe to work at that voltage. The voltage regulator on the board, a 7805, should be fine up to around 20v, but since it's a linear regulatory, it would get very hot at that input voltage. You should be fine connecting it directly to your car's battery/a cigarette lighter port on your car/etc. The most you'll probably ever see at your cigarette lighter is around 13v.

Don't forget to put a fuse on the power line coming from your car. If something shorts you want the fuse to blow instead of something catching on fire. Lead acid batteries are prone to thermal runaway when shorted. Higher temperatures decrease the internal battery resistance causing more current, causing more heat... That's the same reason it's harder to start a car in cold weather, the battery's internal resistance is higher when it's cold.

Encryptic is right to suggest waiting to see if you hear from someone experienced with AVR programming. You might also ask for help in the AVR forum here.

[smp4488]

Would i need just a regular 12V fuse?

[daemondust]

I think there should be a fuse to the cigarette lighters in your car, so you may be able to get away without adding an extra one. If not, then you can use a regular car fuse, probably a 1 or 2 amp one.

[smp4488]

Ok so i can just run my 12V line from the fuse box?

[Encryptic]

I think there should be a fuse to the cigarette lighters in your car, so you may be able to get away without adding an extra one. If not, then you can use a regular car fuse, probably a 1 or 2 amp one.

some adapters have one built into the pin that connects in the middle.

[daemondust]

I hope I don't sound discouraging to you. All too often I've seen people get burned (literally) by not worrying about safety. Safety really needs to be thought about in the beginning, not added in at the end, of a project.

[Encryptic]

I hope I don't sound discouraging to you. All too often I've seen people get burned (literally) by not worrying about safety. Safety really needs to be thought about in the beginning, not added in at the end, of a project.

Plus, burnt electronics make a very poor air freshener. Letting out the magic smoke is bad.