I’m working on a project where I’ll have a keyfob that transmits to a receiver in my car. The receiver being attached to an Ardunio, which in turn will, well, do stuff.
My issue is that this is a “permenant” project. As in I intend to leave it in my car for months at a time. It always needs to be powered/listening for the keyfob signal.
I’ve been doing a lot of reading tonight on hooking an arduino to a car battery and have read that you’ll blow your arduino up if you start the car with it powered on. I’ve read about using a ciagrette lighter adapter - but the problem is my cigarette lighter is unpowered when the car is off.
Another concern is battery draw. I considered using a transformer of sorts to step down and regulate the voltage, however, won’t this be an unnecessary drain on the battery?
Basically - whats the best way to step down voltage from my car to 5v, that’s always on, but has very reasonable battery drain and I can leave it on for a week without starting my car, and come back and the battery isnt dead?
Worst case I can get an external batter to power the arduino, that, when the car is running, charges from the cigarette lighter, and if it dies after a day or two of non-use, so be it.
But I’d really like to full time power from the car battery, with as little drain as possible.
I’m sure someone’s done this before, but for all the searching I’m doing, I’m not seeing it…
You probably want a switchmode step-down regulator, to minimise battery drain & power dissipation, unless you’re only drawing a small amount of current (code optimisation may mean that the micro spends most of its time in a reduced power state when the car’s ignition is off). Look at something like OKI-78SR range (although if you don’t need much current there would be more efficient solutions):
http://www.digikey.com/product-detail/e … ND/2259781
As you suggest, voltage spikes / surges can be a HUGE issue with automotive circuits. As a minimum, put some very beefy TVS / tranzorb diodes on the power supply input. Choose voltage ratings that will not conduct in normal use, but will clamp the voltage below the rating of the voltage regulator (36V in the case of the OKI-78SR). I’d suggest nominal 16V or 18V devices.
As well as the power supply input, make sure you protect any other pin of the Arduino that interfaces to external circuits or other parts of the car. As a minimum, this could be a resistor of a few K-ohms (the internal protection diodes of the micro provide some protection), although sometimes you need to include other protection devices.
i prefer the sub-miniature thermonuclear breeder-reactors the size of a prescription pill bottle and only requiring a steady supply of liquified nitrogen or helium for coolant… low maintenence stuff :0)
i prefer the sub-miniature thermonuclear breeder-reactors the size of a prescription pill bottle and only requiring a steady supply of liquified nitrogen or helium for coolant… low maintenance stuff :ugeek: :0)