Voltage drops significantly with LilyWire

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DaanSon
 
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Voltage drops significantly with LilyWire

Post by DaanSon »

I build a circuit that connects 7 Lilypad VibeMotors in parallel with a Lilypad atmega board, via LilyWire conductive yarn. When I hook this up to my computer and upload a code to one by one test the different VibeMotors the voltage drops significantly meaning at the 3rd motor you don't feel any vibration anymore. To activate the motors separately I added a PNP Transistor BC557 to each motor to act as a switch.

The first motor receives 2.7V, but at the second motor, this is already half.

What am I missing or doing wrong? I paid quite some money for the components so don't feel like solving it in another way.

Thanks

,Daan
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dastels
 
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Re: Voltage drops significantly with LilyWire

Post by dastels »

Based on the specs, it takes 85mA to get one of those motors moving (and 2.3v). That wire has a resistance of 28 ohms/ft. That's a voltage drop of 2.38 volts/ft.

Now, power to the motors, is that all on one wire, or on separate ones? How far apart are the motors?

Even with separate power lines to each motor, if your third motor most certainly doesn't have enough voltage to get it moving.

The solution is to use "wire" with lower resistance. That means real wire instead of conductive thread, and as thick as you can get away with in your application.

Something like https://www.adafruit.com/product/1881 is good. Still thin and flexible, but has a resistance of 123 ohms/km. That's ~0.04 ohms/ft. Compared to the voltage drop calculated above (for a single motor) that's 0.003 volts/ft.

Dave

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DaanSon
 
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Re: Voltage drops significantly with LilyWire

Post by DaanSon »

Hi Dave,

Thanks for your quick reply.
That is what I was assuming indeed. The motors are each approx 10cm apart and powered by a single powerline. At least now I know that my hunch to switch to real was correct.

Appreciate the wire suggestion as well, I'll look into what is easily obtainable in my country (The Netherlands).

Daan

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dastels
 
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Re: Voltage drops significantly with LilyWire

Post by dastels »

The silicon coating doesn't matter so much, but it is nice to work with (doesn't melt when soldering and is VERY flexible). 28 or 26 gauge is probably a good idea for the power lines, and being stranded rather than solid is imperative to have it flexible.

Dave

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