Incorrect functioning of Arduino UNO when not connected to Serial

Other Hardware General Electronics
1

Hey all!

I'm working on a project (basic collision avoiding robot) and I'm running into a problem. The robot works fine when it is connected to my computer's USB port via the serial port on the UNO, but the second I run it with external power only it does things that are not in the code (spinning in circles, humping the floor[it was interesting], etc.). I've tried changing the boot-loader and re-installing drivers and bridging the RX pin to the Ground pin with a resistor and using different batteries . . . Nothing.

Has anybody else had this problem?

2

Is the power supply on the second arduino stable?
Did you try power it using bateries?
I belive you only have a power problem.
What is the Voltage you are appling to it in the DC jack?

3

I don't believe so. I'm using only one Arduino with the Arduino motor shield and I've tried different batteries. I tried using a 9v battery and then a 6v battery pack and neither fixed the problem.

4

Sounds like a power problem.

Try measuring the voltage on the Arduino.

5

I have 5V going to the Ping sensor I'm using and 3V going to each motor. The battery pack I'm using is 6V.

6

DYE_ABel:
I have 5V going to the Ping sensor I'm using and 3V going to each motor. The battery pack I'm using is 6V.

Measure it again. 6V isn't enough for the Arduino regulator to function properly so you can't possibly have 5V on the Arduino.

PS: 4 normal batteries doesn't give 6V unless the batteries are brand new. Measure that voltage, too.

7

DYE_ABel:
I tried using a 9v battery and then a 6v battery pack and neither fixed the problem.

9V battery, especially the small rectangular type, will not provide enough current to function properly. 6V isn't enough to function properly either.

You really want something in the 7-9V range that can supply at least 500mA.

If you go much over 9V, the on-board regulator might start shutting down if you're drawing close to 500mA.

8

I just tried powering the shield and Arduino with two separate (kind of oldish) 9V batteries and it SEEMS to be working better.

9

Like all we say it's a power problem :grin:

10

Yep . . . :sweat_smile: