I'm using a tip120 transistor to control some flexinol SMA wires. I can easily get one to work, but seem to be having issues when I try to drive both the wires with one power source, I'm assuming it has to do with fact that the current is being split between the two wires? and if so, not sure how to increase the current between the two-- would I just increase the voltage? with SMA it seems that current is the most important part.
if I increase the current I am not sure if that is ok with the tip120-- just started using these.
here is a schematic of how I am wiring it: https://www.dropbox.com/s/2fp01vgoz050r7h/Screenshot%202013-12-13%2012.01.28.png
the battery is actually a 9v 30mA transformer though, R1 is 2.2k and other resistors are the SMA wires.
here is also a link to the breadboard that can be forked http://123d.circuits.io/circuits/70276/