designing SMA wire control project using arduino

Forum 2005-2010 (read only) General Bar Sport
1

First of all this is my first post and I really doesnt know much about hardware, software,electronic,mechanical,etc so please allow me to be silly most of the time. i decided to put my post here because i felt that in the hardware forum is too advance for me lol. Please give me some advices how normal or tell me if u see anything

Objective of my project : control three or more SMA(shape memory alloy) wires and have feedback control using their resistance reading.

Workflow concept 1:
[input a desire length into the computer]
[ch8595]
[the length is converted into a resistance value and
output to digital potentiometer]
[ch8595]
[feed 5v to both SMA and Digital potentiometer alternatively]
[ch8595]
[compare the voltage of the pull-up resistance(not sure if i get the term correctly please refer to the photo)
print the reading into the computer for data logging]
[ch8595]
[if the voltages are different, control the time of the different time of the power supply to the sma. eg feed the current long enough to make it contract or have the resting time long enough to just to keep it at constant length]

Workflow concept 2:
[input a desire length into the computer]
[ch8595]
[feed 5v to both SMA]
[ch8595]
[read the voltage and the current across the SMA and print the value into the computer]
[ch8595]
[control the PWM while using the reading as feedback control]

Actually what I dont understand and really in trouble now is

  1. the SMA wire's resistance is so low, it change from around 0.6ohm-1.0ohm, how should i choose my other resistors in the circuit?
  2. should I use the arduino output port as power supply ? or just use it to control the transistor(switch on/off)
  3. i read about "processing" software to log data from arduino from Getting start with Arduino book but dont really understand it. Can anyone please explain how it should work to me :-/ in the mean time i will just check processing.com

Thank for reading until the end. sorry for having too many unknowns and questions :smiley:

Great day to everyone and enjoy your spring.

2

I did not fully understand what you want to achieve. The maximum current rating for an Arduino chip is 200mA. Not for one output, this is for the while chip. The outputs can source at most 40 (or maybe 50) mA.

Since your wires have ~1 Ohm you would get more something like 4-5 A from a 5 V source. So this is far away from what an Arduino can source. You need to consider some Transistor in between to amplify the current.

Udo

3

Thank you Udo for commenting and for the very useful information.
So I would have to get the independent source of power from somewhere else and only use the Arduino to control the Transistors.

And use a comparator to compare the value of the voltage with the potentiometer. Now you made me understand more.

anyway I am reading about "processing" now to display the data from the arduino on my computer. And hopefully to control the arduino in the future from the same user interface windows