Power Supply?

im going to be running this two motors out of my arduino : http://www.pololu.com/catalog/product/61 and 1 servo parallax http://www.parallax.com/tabid/768/ProductID/101/Default.aspx

Also im planning to put a serial LCD (to save pins) :frowning: and a LED light…

Whats my best bet as power supply?

btw im using the adafruit motor shield

You shouldn’t need an additional power source to run that. A good 9V battery pack on the arduino should cover it. That or a good wal-wart.

i read few post of people saying that 9v are not that good to run motors that AA are better… should i just get like a 4cell battery holder so it will be 6v? will that do it?

  1. The 7805 voltage regulator takes a minimum of 7. something volts to work

  2. yes a fist full of AA batteries will last longer than a 9 volt, but then you have a fist full of AA batteries

ohh then i will need a 6-cell holder… ummm i may stick with a single 9v… Any of you guys have experience running 3v using that motorshield?

or im better off using a 9v battery for my arduino and then connect external power to the motors, posibly using a 4cell battery cage

Everything you want to work with only needs 5V so running it off the Arduino is fine. no need to play around with an external power source unless your ready to regulate it doen from 6V to 5V so you don’t burn out the arduino accidentally feeding that 6V directly into one of the pins.

wouldnt that stress the Arduino’s voltage regulator?

eh the 7805 is rated up to an amp … but not with the way its setup on the arduino

your good to go for a few hundered ma, guess we need to figure out how much load is going to be on it

how do i figure that out?

also if i run everything from a 9v the battery will get consumed very quickly right?

how do i figure that out?

Start looking at the items your going to run. They will all have spec sheets telling you the min and max voltages they use and how much current they ca draw. Find the max current for all items and add them up. Now you know how much current they will all pull if they are all running maxed out and doing so at the same time.

If you have everything running full bore constantly then yes a 9V can be drained quite fast. But a 9V is a good place to start. If run time becomes a concern you can always turn to using 4 to 6 D cell batteries. Though a better option may be using a 9.6V battery pack from an RC car. Those are made for running heavy loads like motors running hard.

well here is the data sheet for my 2 motors… (Mine are FA-130RA-18100) http://www.pololu.com/file/0J11/fa_130ra.pdf

seems like under load it uses 0.56A. So 0.56*2 = 1.12A at load

Note that a 9V battery PACK is not the same as a 9-volt battery. You’d use 6 or 8 rechargeable AA or AAA cells in a holder. And for running motors, rechargable is the way to go, unless you really like buying non-rechargables by the case :slight_smile:

8 cells is probably a better choice than 6, since a NiMH cell puts out around 1.2 volts, rather than the 1.5 of a non-rechargable alkaline cell.

Well i was thinking about using a “9V battery” for the arduino and then a 2-cell AA (3V) for the motors and connect it to the ext pwr on the motor board

well i got the motors in today and they wont run using a 2cell battery when i take the jump the motors try to move but it never happens, if i remove this 2 cell holder and put the jumper back in and run everything using the 9v it works fine but… i have issues… if i use this code:

#include <AFMotor.h>

AF_DCMotor motor1(1);
AF_DCMotor motor2(2);

void setup() {

motor1.setSpeed(200); // set the speed to 200/255
motor2.setSpeed(200); // set the speed to 200/255

void loop() {

motor1.run(FORWARD); // turn it on going forward
motor2.run(BACKWARD); // turn it on going forward


Both motors will spin forward and everything seems to work… but if i add a reverse action or a delay the motors will get stock like they will try to work but they wont start and then it works then it stops… im going to try to put a cap 0.1 in the motor connectors tomorrow and see how that goes…