Arduino Forum

Using Arduino => General Electronics => Topic started by: ragonamuffin on Apr 26, 2011, 10:11 pm

Title: Flexiforce sensor with arduino, and only +5 volts
Post by: ragonamuffin on Apr 26, 2011, 10:11 pm
I need help modifying the following schematic to accommodate essentially the arduino power and nothing else. I tried switching the flexiforce pin from the inverting pin to the non-inverting pin of the op amp then powering it with +5v, but that did not work. I don't know the first thing about designing circuitry, so any help is greatly appreciated. I have done tons of googling with no luck.

If I have to use circuit, how I can get a -5 volt supply out of the 5v supplied on the arduino?

Thanks to anyone who can help me, I have been trying to solve this on my own for a couple days.

(http://localhostr.com/files/kTws91T/Screen+shot+2011-04-26+at+3.55.57+PM.png)
Title: Re: Flexiforce sensor with arduino, and only +5 volts
Post by: RuggedCircuits on Apr 26, 2011, 10:20 pm
You could just make the flexiforce sensor one of the 2 resistors in a standard voltage divider:

http://en.wikipedia.org/wiki/Voltage_divider

You will get a less linear characteristic between voltage and applied pressure, but no op-amps required!

--
The Gadget Shield (http://ruggedcircuits.com/html/gadget_shield.html): accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons
Title: Re: Flexiforce sensor with arduino, and only +5 volts
Post by: ragonamuffin on Apr 26, 2011, 10:32 pm
That is actually how I had it set up initially for testing when I was using a less sensitive force sensor. I am now using the 100 pound sensor I plan to use with my project. This one is just so insensitive though, I figured I would set it up the way the schematic told me to. I am using a 10k trimpot shown below for my project. Maybe I need a larger trimpot (100k) to get the results I need? I could probably whack it with a hammer and have it barely light up the reference LED. I need it more sensitive than that lol.

http://www.sparkfun.com/products/9806 (http://www.sparkfun.com/products/9806)
Title: Re: Flexiforce sensor with arduino, and only +5 volts
Post by: elandd2011 on Apr 26, 2011, 11:06 pm
See this
Title: Re: Flexiforce sensor with arduino, and only +5 volts
Post by: elandd2011 on Apr 26, 2011, 11:10 pm
see this also, i can work for you
Title: Re: Flexiforce sensor with arduino, and only +5 volts
Post by: ragonamuffin on Apr 26, 2011, 11:56 pm
Thank you very much for that! Is that IC this op amp?

(http://s3.postimage.org/7xiv8c21v/Screen_shot_2011_04_21_at_6_43_19_PM.png)
Title: Re: Flexiforce sensor with arduino, and only +5 volts
Post by: elandd2011 on Apr 27, 2011, 12:02 am
yes LM741