dc motor + muscle wire power supply question

Hi all, first post here. I've been trying to find the answer in other people's posts, but didn't quite get there, so here's my little scenario. I'm working on a project where the arduino NG controls a 12v dc motor (lots of pwm planned) and an array of 6 muscle wire "levers". I understand that I must use a separate power supply (plus transistor circuit) for the motor. I've been testing the lever array (without arduino) by running it through a voltage regulator 7905, which seems to work well. The motor and array are on the same power supply and seem to get along ok. My question is: once the arduino is part of the circuit, do I have to add transistors to all 6 of the levers as well? Or is the fact that the voltage that reaches them is harmless to the arduino makes it unnecessary? I can't imagine blow back is an issue with MW, right? Thank you in advance for any thought on this. This forum is always an inspiration.

Oh, I should mention as well that I'm using the ping sensor running right out of the arduino.

Have you measured how much current your MWs use? I think they are fairly power hungry.

I haven't actually measured, but trying to figure it out from their data sheet (and this is where my inexperience catches up to me), it should be 6mA per lever. They will be activated at the same time sometimes (but not for very long and unlikely that all 6 at once). Let me know if this doesn't make sense.

Do you have a link to the MW information? 6ma seems a bit low from what I remember when I checked on MWs.

http://www.jameco.com/Jameco/Products/ProdDS/357595.pdf I'm using 20cm of the 100HT for each lever. Thanks for helping out!

Well, looking at the data sheet, the 100 wire appears to have a resistance of 150 ohms per meter. You are using a 20cm piece, so it will have a resistance of 30 ohms. The sheet appears to say the optimum operating current for the wire is 180ma, so you will need to pass 180ma thru your section of wire. Using a 5v supply, your section of wire should pass ~167ma, pretty close to the target value. I doubt the Arduino can source this amount of current directly. You probably need to use a transistor to control your current from the 5v source. Note that there may be some voltage drop across the transistor, so you may want to look at increasing the voltage output of your voltage regulator to get closer to the 180ma current. A simple thing you can do is put a small diode on the ground of your voltage regulator to increase the output to 5.7v. I'm not an expert, so the above may or may not be correct, so YMMV!

You defiantly will need a transistor or FET to power muscle wire from an arduino.

It is OK to run the motor and the muscle wire off the same power supply. I wouldn't bother about increasing the voltage to the wire as the odd 0.7v is not going to make much difference in pull in time. The more the current the faster they pull in. make sure the ground of your extra power supply is connected to the ground of the arduino.

This is great. Thank you very much! Now off to designing the circuit board. I'll post a link to the finished project once I get there.