PWM Current Ouput

I want to use the Arduino Uno to trigger a muscle wire that reacts to heat. Plugging the Arduino to a USB port could only generate a maximum of 0.5A through the wire and i actually need something around 0.6-0.8. I read here that if you plug the arduino to an external power supply with a higher voltage the current limitation might be higher. is it right? and if so, will it also apply to the PWM pins?

Thanks a lot

How do you drive that wire? A digital output (that includes PWM) can only do 40mA absolute max. So better stay at 20mA.

If connected to USB then the USB port is the limitation. You can use an external supply but don't power the memory wire from the arduino 5V then. Just grab a USB charger and just split the USB cable to tap off the 5V. You can still power the Arduino via USB from that charger. You can even plug the arduino into a PC and use that charger only to power the wire but then don't forget to attach the GND of the charger to the Arduino.

You cannot drive that sort of power direct from an Arduino pin, the arduino pin is for signals, not power, and can manage an LED or two at most.

Typically a transistor or logic-level MOSFET would be used to increase the current capability.

MarkT: Typically a transistor BJT or logic-level MOSFET...

Sorry 0:-)


Are you familiar with [u]Ohm’s Law[/u]? Ohm’s law describes the relationship between voltage, resistance, and current. “Resistance” is the resistance to current flow, so more resistance = less current. And, more voltage = more current.

Do you know the resistance of your muscle wire? (The resistance is probably specified in Ohms-per-foot or Ohms-per-meter.)

The bottom line is, you’re probably going to kill your USB power supply (hopefully only temporarily if you’re lucky) if you connect the muscle wire. The resistance will be too low, you’ll get too much current, and the voltage will drop.