# arduino+ memory (muscle) wire

Hi,
I started to experiment with memory wire which contracts according to current and relaxes with gravity…
I’m wondering if anyone tried to run it with arduino?
The wire needs current up to 5V to fully contract… Im not sure if it safe to try to control it with potentiometer…
Would anyone know?

cecylia :-/

Muscle wire works by heating usually by the current flowing through it. The heating current required is measured in amps or milliamps, the current that 5 volts pushes through the wire depends on its resistance which is affected by its thickness, what its made from and its length. The arduino could control it directly if it uses less than 40 mA or via a transistor or relay if it uses more than 40mA. Where does the potentiometer enter into the equation if you’re driving it from the arduino ?

Do you have a multimeter? For something like muscle wire, each different length you cut will have a different resistance, and you can’t design circuits around it unless you know that resistance. Theory (eg if you know how many ohms per metre for your size wire) can help - but, if at all unsure, it is easier to simply measure it. Hence the multimeter.

Then you can just use Ohm’s law, V=IR, to find out how much current it will draw when you put a given voltage across it - or, conversely, how big a resistor you need in series with it to limit the current to the desired amount. (hint - you will need a limiting resistor AND a drive circuit eg transistor)

Do you know the exact make of your muscle wire? Manufacturers usually write data sheets which tell you the stuff’s properties, and they often include example circuits that can be very informative.

Muscle wire works through heating and normally takes about half an amp. This is way too much for the Arduino’s output so you need a relay or transistor to switch it. You also need an external power supply to give that sort of current.

The same is true of a potentiometer, most will not be able to stand so much current. A carbon pot will just vaporise if you have so much current flowing through the end track. Of course you can get wire wound pots but these are bulky and expensive. I did have several 1KW pots for controlling theatre lights years ago they were over two feet long.