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### Topic: How to choose the right resistor for the flex sensor (Read 434 times)previous topic - next topic

#### jack1992

##### Jul 29, 2016, 02:13 pm
Hello to everyone.I want to buy a flex sensor(4.5'') to experiment with it and i was wondering how to choose the right resistor.On the internet and the forums says that the 22K is good choice but it's my first time with flex so i need your opinion.Thanks in advnace.

#### DrDiettrich

#1
##### Jul 29, 2016, 04:23 pm
What's the purpose of the resistor?

If you need it to build a half-bridge, a first guess is the value of the sensor itself. If the sensor has very little resistance, chose a value that provides convenient current through the sensor, e.g. the suggested 22k. If then the signal range is too small, a full (Wheatstone) bridge and an opamp can be used to amplify the signal.

#### jack1992

#2
##### Jul 29, 2016, 05:05 pm
What's the purpose of the resistor?

If you need it to build a half-bridge, a first guess is the value of the sensor itself. If the sensor has very little resistance, chose a value that provides convenient current through the sensor, e.g. the suggested 22k. If then the signal range is too small, a full (Wheatstone) bridge and an opamp can be used to amplify the signal.
I want to build this:
http://www.instructables.com/id/DIY-Robotic-Hand-Controlled-by-a-Glove-and-Arduino/

on the step 3 of the instructable says to use 22K resistor.I am confused.Every flex sensor can handle 22K resistor?

on this page says(https://www.adafruit.com/product/182)
If they're unflexed, the resistance is about ~10KΩ. When flexed all the way the resistance rises to ~20KΩ.

on this page says(https://learn.sparkfun.com/tutorials/flex-sensor-hookup-guide)
This circuit requires one resistor. Many values from 10KΩ to 100KΩ will work.

so according to sparkfun 22K will do, right?Thank you for your time

#### DrDiettrich

#3
##### Jul 29, 2016, 06:25 pm
When you study Ohm's law, you can calculate yourself how much the voltage on the center tap of a half-bridge will change, when your sensor varies its resistance between 10k and 20k, depending on the dummy resistor. Give it a try, you'll need it every now and then.

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