8 years, 7 months ago.

Helllllppp Measure -5V to +5V Voltage


Hii everybody,

Can some body help me please? I want to measur the Vout Voltage with the Analog_pin my question is how to connect the mbed to get right measurements?

Thank You!

2 Answers

8 years, 7 months ago.

Your diagram doesn't show how you are powering your Instrumentation Amplifier (IA). If it is ground referenced then simply adjust the gain of the IA to have your full signal swing from the bridge fall in the 0-3.3V range of the A/D input. If it is powered by a +/- power supply then you will have to level shift the output with another amplifier to a 0 to 3.3V input to the A/D. However, since your bridge is unipolar (ground referenced) I am not sure why you would use a +/- power supply for your IA.

Sorry for the late answer.. I was on vacation... i use a TL084 OP powred with +-12V to: 1) calculat the difference between V1 and V2 2) and after to ampilify the Output Voltage Vout

my Problem is that the Microcontroller is powred with the USB and it can mesure just from 0V to 3,3V and my Bridge and the amplifier are powred with another extra voltage source (12V). and the Vout is from -5v to +v

posted by Amin Ke 03 Sep 2015
8 years, 7 months ago.

I think you should use single supply amplifiers with half supply (1/2 Vcc) referenced.. So in that case, when V1 = V2 the output will be the half of supply voltage, if you use rail to rail op amps and feed them (and the bridge of course) with 3v3 then you won't have to adjust anything extra, you can connect the output to directly to MCU's A/D input (may be with an additional current limit resistor like 100R something)