Jittery input from motor shield

Other Hardware Robotics
1

Hi forum!
I am new to electronics so this will probably be an easy question for most of you.

I have an arduino uno R3 hooked to a arduino motor shield R3. The arduino is powered from usb and then the motor shield is connected to a 9V battery through the Vin, GND.

The problem is that when i read values from the unused pwm pins or the analog pins I get very jittery values. The pwm behaves strange and seems to give 1s and 0s at random, and the analog reading is stable until you use the motor which makes the reading of a sensor through those pins impossible (right?) without the use of some kind of filter.

Is this normal behaviour for a motor shield, and if it is how do you get sensor input?

Thanks!

2

If you have nothing connected to a pin and you read it, then you will get random values. It is picking up electrical noise, you have what is called a floating input. Connect sensors and a pull up resistor and it will stabilise.