Tuesday, 14 May 2019

operational amplifier - What is the best interface circuitry for using FSR sensors?


Force Sensitive Resistor (FSR) is a sensor which lowers its resistance when there is force upon it. If there is no force acting on it, the resistance is ~10MOhms.


Looking at Interlink's guide (here) and FlexiForce's A401 datasheet (here) here are interface circuits which are recommended:


1- Simple Voltage Divider

Pros: simplicity
Cons: ADC impedance introduces distortions in measurements


2- Voltage Follower via OpAmp (buffer)
Buffer Pros: Input resistance of OpAmp is near-infinite
Cons: There is offset error due to OpAmp


3- Adjustable Buffer
adjustable buffer
Pros: Gain and offset can be tweaked
Cons: Rather complex,IMO


4- Transimpedance Amplifier

Pros: Conductance/Force of FSR seems to be more linear that Resistance/Force
Cons: ???
transimpedance amplifier


Note that there is a limit on the current flowing through FSRs. The circuit should also take that into account.


1- Are there any other circuits for this application?
2- What is the best configuration for (A) Calibration and (B) Normal Use?


Here are my other questions related to FSRs:
What is meant by "adjustment of the output gain and offset" of a Force Sensitive Resistor interface circuitry?
What is the maximum force that a FSR sensor can detect?


FSR sensors have both creep and hysteresis. That is one issue. The other issue is a good interface circuit which both limits the current and produces zeros offset and noise.





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