I want to interface a flex sensor to my PIC18F and I am facing some trouble doing so. The flex sensor is a resistance based sensor, so I am using a voltage divider circuit with the appropriate fixed resistance to obtain the voltage outputs from the sensor. The below are the images of the circuit I simulated in Multisim.
Here is the link to the datasheet of this sensor:
http://media.digikey.com/pdf/Data%20Sheets/Spectra%20Symbol/FS%20Series%20Flex%20Sensor.pdf
The above image shows a close up view of the flex sensor.
Now the problem is:
1) When I rigged up the hardware for the simulated circuit, I noticed that there is a drop of 4.85V across the sensor, for a flat resistance of 10K while it should give 1.667V. And bending the sensor does not show any variations. Therefore I am getting wrong output.
2) Then to verify the sensors Flat resistance, I connected its both the terminals to a meter and noticed that there is no resistance being displayed on the meter, even after varying the meter to check from 200 ohms to 2Mega ohms, but it displays nothing.
From, point one I presume that, I may be doing something wrong. From point 2 I presume that (since the sensor is pretty old), the sensor may have got damaged.
However, how do I come to these conclusions and is my circuit right? and how to check if my sensor is working fine?. Any advice's regarding this would be helpful. Thanks in advance.
Best Answer
Your circuit has an impedance that is a bit on the high side for direct (no buffer) connection to a PIC ADC input - usually 2.5K to 10K, depending on the model, is the maximum recommended. Yours could be as high as 17K, so a buffer amplifier might be a good idea,
However if the sensor doesn't read sensibly on the multimeter ohms function, but the meter does read approximately correctly with 10-110K resistors, then the sensor is broken, and securing a replacement would be the first step.