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Hello,

I am fairly new to the Arduino and am looking for the best way to power my project. I am working on an RFID ignition switch for a scooter. Here is a link to the battery they run off of:

http://www.amazon.com/YTZ7S-AGM-Maintenance-Free-Battery/dp/B0038MI338/ref=sr_1_2?s=automotive&ie=UTF8&qid=1335307216&sr=1-2

It is a 12v battery. The scooters do have a charging system as well. The only accessories that really exist are headlights, horn, turn signals and brake lights. I was contemplating just connecting it straight to the battery but fear that is not the safest bet. I was thinking of using the regulator circuit outlined here:


http://www.eidusa.com/Electronics_Voltage_Regulator.htm

I have a 7805CT lying around that I could use in my prototype. What would be the best course of action? Am I safe to just use the 12v power from the battery or should I incorporate a regulator?

Thanks in advance.
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What are you plugging in? An Arduino board? That already has the regulator on it. Perhaps describe your exact hardware.
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I will be plugging in the Arduino Uno (As it says in the topic). I am aware that it already has a regulator, but should I be worrying about how clean the power is going to the board? In addition I will also be using an RFID reader (ID-12) plugged into the Uno. Here is a link to the RFID reader:

http://www.sparkfun.com/products/8419

When a fob is scanned and passed it will switch on the 12v ignition to the scooter (either using a transistor circuit or a relay). In addition I was going to offer a couple of "Accessory" outputs. The outputs would just switch the 12v on to an output for an accessory.

Hope that answers your questions.
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Quote
I am aware that it already has a regulator, but should I be worrying about how clean the power is going to the board?
With 12V going-in and the Arduino only needing 5V, you are giving the regulator plenty of "room to work" and the voltage regulator should hold the voltage steady.   So, the on-board regulator should be fine.   If there's any noise or glitches getting through, a 2nd or different regulator is unlikely to help.   

If you do run into problems, such as the voltage dropping too-low for a moment when you hit the starter, or when you first turn-on the headlight, etc., you can try adding a diode and capacitor (maybe 1000uF or so) to the 12V input.   This makes sort-of a "one-way" filter... It won't do much for positive spikes on the power-supply line (the regulator should take care of that), but if there is a negative-spike where the voltage momentarily drops below 5 or 6 volts, the capacitor will hold-up the voltage (hopefully long-enough) and the diode makes sure all of the energy stored in the capacitor goes to the Arduino, by  prevening the capacitor from quickly-discharging into the overall electrical system, and "trying" to power everything else on the scooter.

And actually... as long as the thing resets properly when the voltage drops-out, and it doesn't shut-down the scooter when there is an unexpected reset, it's probably not too critical .
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I am aware that it already has a regulator, but should I be worrying about how clean the power is going to the board?
With 12V going-in and the Arduino only needing 5V, you are giving the regulator plenty of "room to work" and the voltage regulator should hold the voltage steady.   So, the on-board regulator should be fine.   If there's any noise or glitches getting through, a 2nd or different regulator is unlikely to help.   

If you do run into problems, such as the voltage dropping too-low for a moment when you hit the starter, or when you first turn-on the headlight, etc., you can try adding a diode and capacitor (maybe 1000uF or so) to the 12V input.   This makes sort-of a "one-way" filter... It won't do much for positive spikes on the power-supply line (the regulator should take care of that), but if there is a negative-spike where the voltage momentarily drops below 5 or 6 volts, the capacitor will hold-up the voltage (hopefully long-enough) and the diode makes sure all of the energy stored in the capacitor goes to the Arduino, by  prevening the capacitor from quickly-discharging into the overall electrical system, and "trying" to power everything else on the scooter.

And actually... as long as the thing resets properly when the voltage drops-out, and it doesn't shut-down the scooter when there is an unexpected reset, it's probably not too critical .

Perfect.. That is exactly what I was looking for.. Thanks for a great reply. I never thought about the power cut out when trying to start. That is something I will need to test thoroughly as it could potentially shut off the ignition while trying to start.

Thanks again for the help.
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