fabricsensorvoltage divider
I'm researching conductive fabric with a surface resistivity <0.5Ω/m2 (unstretched).
I've used a voltage divider setup to connect with an ADC pin of microcontroller (ATMega/Arduino board).
This setup works, but the fabric gets hot to the touch.
I suspect this is due to the low resistance and too much current going through. Is this correct? Are there other possibilities for this occurrence?
I don't really see a reason for this not to work the way you expect with the connections you have listed here. Might I suggest some debugging steps?
1) See what happens to the output range when you put a large-ish Rg ( say 27k ohms) in the circuit. Does the output swing change at all? 2) Have you checked the inputs to make sure they are as you expect with the amplifier connected? If so, how about using a larger resistance POT to simulate your resistor divider just to remove the sensor from the picture until you get the circuit working. 3) Perhaps the simplest explaination might be that the INA126 itself is bad. Do you have a spare you can drop in to test?
This seems to be very similar to Nick's schematic, was probably busy drawing it when he posted :-).
First why you can't use the N-FET on the high side: it needs a gate voltage a few volts higher than the source, and the 4.2 V is all you have, nothing higher, so that won't work.
I have a higher value for the pull-up, though a value of 100 kΩ also will do. 10 kΩ will cause an unnecessary extra current of 400 µA when you're measuring. Not the end of the world, but it's 1 resistor in both cases, so why not use a higher value.
For the MOSFETs, there are a variety of parts to choose from given the requirements are not so strict; you can consider inexpensive ones such as, e.g., Si2303 for the P-channel and BSS138 for the N-channel.
Best Answer
an offline friend just suggested using a wheatstone bridge.