Hello, I am trying to hookup the ADC of my 7" friendlyarm on an automotive pressure sensor. The sensor is a variable resistor from 0 to ~50ohm to the ground of the vehicle. Does someone here have a good idea for me how to hook it up? The only thing I can up with is putting a "user" of 100ohm in the 5V. line feeding it in the sensor and the ADC so when pressure/resistance changes the ADC reading too...
It will use more than 1W, could damage your sensor. Try constant-current source to sensor than tap and scale the voltage to 0-3.3, this way you will have the full 10Bit resolution Example. http://www.allaboutcircuits.com/vol_6/chpt_3/14.html
this one might be better to understand http://www.aeroelectric.com/articles/LowOhmsAdapter_3.pdf
Nice Dezso, thank you!
Made a constant current source with a LM317 and a power supply for the ARM with a DC-DC convertor but I am measuring 3.5V max for my ADC powers and are suddenly wondering how much the ADC can take. Wil 0.2V more kill it? (I doubt that my readings are correct, cheap meter, the DC-DC converter shows 5.2V so both readings are 0.2 higher but I would hate to fried the ARM)
Use some Precision Potentiometers like 10k, 1-GND, 2"Center"- ADIN 3-Constant Current output, than adjust your pot to get the correct reading. Technically you will never get the full source voltage on the output unless the sensor not connected, since the sensor min and max resistance will be always less the infinity, "0 to ~50ohm" You can also use LM334 in TO95 package. Check this picture, http://img296.imageshack.us/img296/4408/rmkr2.jpg you want to build the 10ma section !
I meant will 3.5V on the ADC destroy my board?
DC supply voltage for analog core VDD 3.3V VDD Min 3.0V Max 3.6V
I am assured now, thanks!
