Flexinol and Arduino

Hello everyone!

I want to do a project using flexinol -muscle wire (https://grobotronics.com/flexinol-0.005-diameter-1-foot.html?cookies_accepted=Y ) in order to move a structure made basically out of some kind of fabric. I want to send data wirelessly via another Arduino-which is hooked up with sensors- to the one attached to the fabric and flexinol wire , via Bluetooth , in order to control when the wire will heat up and therefore 'move' by changing shape. I have found several projects but I'm not quite sure which circuit is the right one so that i don't burn my arduino uno.
Does anyone have any ideas about which circuit is the best for connecting arduino and providing heat through it to the Flexinol Muscle wire?
So far i have understood that I must use a transistor (most people use TIP20 i think) or MOSFET (i have MOS Irf520 is this a good MOSFET?) to control the current that passes throught the circuit to the wire and also use an external battery too. Do i need a seperate battery for the Arduino and another battery for the wire? I see most people use Lipo batteries. The specific wire i am showing you needs 320mA.
Also i wanted to ask, in order to make my calculations for the resistance correct, how do I define the Volts? According to the external battery source or according to the Volts the Arduino gets??

Also how can i ensure that i don't burn the fabric? Is insulating the wire with silicon tubes for example, ok, or is it better to get a fabric resistant to heat?

Sorry if I'm not expressed correctly, I'm quite new to electronics!

Thanks a lot!

P.S. some tutorials i looked are:

https://www.instructables.com/id/How-to-Animated-Textile-Surfaces/

All your questions are answered in your linked tutorials. If you don't understand what's explained and demonstrated there, try something more simple.

If you use a LiPo. it will be about 3.7 volts. Use a fabric that can take the heat, and that is fairly robust. Woven kevlar seems to be well suited to this application. Activate your wire and do the wireless thing separately at first, so you will have an easier time debugging. I would think you'd want to use two separate power sources. 320 mA is pretty high for an Arduino project.

Also how can i ensure that i don't burn the fabric? Is insulating the wire with silicon tubes for example, ok, or is it better to get a fabric resistant to heat?

You don’t get a lot of pul power with a muscle wire. I would have thought that a silicon tube would be stiffer than it could pull.

Try out your idea with just a direct connection to your muscle wire to a power source to see if your idea is feasible.

A common problem is getting the wire to cool off again. It sorta need open air.
But a flaw in the circuit will allow it to get hot enough to burn through fabric, so be careful!

It’s disappointing that flexinol prices haven’t come down since the early days. And that I lost the sample wire from my kit :frowning:

Hello again and thank you for your answers!

first of all i want to be sure that i don't burn my Arduino since this specific flexinol needs 320mA to change shape..that's why i'm asking my newbie questions..
what gets me more confused is calculating the VoltageInput and output of the arduino, for example when i power my Arduino through USB or through the power jack with a 9V battery, what voltage do i use in Ohm's law to see what kind of resistance I'm going to need? especially if i also use in the circuit another battery besides that powering the arduino, how do i calculate the volts?

Sorry for my silly questions but this confuses me the most and i need to be sure my calculations are right because i can't afford ruining my Arduino or PC!!!

Thanks a lot!! :slight_smile:

what voltage do i use in Ohm's law to see what kind of resistance I'm going to need?

5V. The 9V gets regulated down.

You can not connect muscle wire directly to an Arduino pin.

Well does anyone know how to measure which resistors to pick when we have like two seperated circuits (one for the microcontroller and one for heating the muscle wire) as in the picures below? Because i can't find a clear answer..consider that i will have the Arduino connected to a 9V battery..do i calculate the resistance that connects to the arduino seperately from the resistance that the rest of the circuit (mosfet and muscle wire) needs?

Thank you!

IMO you're trying to kill the green LED, and the Arduino pin it connects to.

Calculate the resistance from the battery voltage and the desired current. This will give the total resistance, from which you subtract the muscle wire resistance. Eventually subtract the transistor CE voltage (~2V) from the battery voltage.

DrDiettrich:
IMO you're trying to kill the green LED, and the Arduino pin it connects to.

Calculate the resistance from the battery voltage and the desired current. This will give the total resistance, from which you subtract the muscle wire resistance. Eventually subtract the transistor CE voltage (~2V) from the battery voltage.

ok but i have two batteries one for the arduino (9V) and one LiPo (3.7 V 320 mA) for the muscle wire.. in this case which volts do i use? do i add them?

The LiPo voltage will be too low for a TIP darlington and the muscle wire. Compute the voltage on the wire at nominal current, and use a MOSFET for switching, to get the minimal supply voltage. Then select a battery and compute the resistor for the voltage difference.