Amreen Ahmed

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11 years, 6 months ago.

Current Sensor

hi guys, I am using a current sensor with an output of +- 4 volts. I am wondering how i can measure negative and positive voltage both from the same source using mbed. The link below is the data sheet of the current sensor i intend to use. www.gmw.com/electric_current/LEM/docs/LEM-HTR50to500-SB.pdf‎

Any ideas or suggestion would be great.

regards

2 Answers

Wim Huiskamp
11 years, 6 months ago.

Basically you need an analog frontend to convert the input voltage to the right range: first use an opamp to add 4 volts to the input signal, which results in 0V to 8V range, then use a voltage divider to reduce this voltage to the valid range of 0V to 3V3 for the mbed ADC. Search the mbed web for examples.

Accepted Answer

any reference please. I have the same problem. i want to convert voltage in the range of +- 3V

posted by Arup Sengupta 18 Jun 2014

There are many examples on the web. Just Google for "voltage adder opamp". Here is a hit: http://www.engineersgarage.com/tutorials/understanding-op-amp-4?page=8

posted by Wim Huiskamp 18 Jun 2014
Ad van der Weiden
11 years, 6 months ago.

It depends a bit on input and output impedances but in principle you can map the source voltage to the mbed input range with three carefully calculated resistors. From the input you connect one resistor to 3.3v, one to ground and one to the source voltage. If you are interested I can compute the values for you. If R1 is the resistor to 3.3, R2 to gnd and R3 to source E then the voltage V at the input is Rp/R1*3.3+Rp/R3*E where Rp is the parallel value of R1,R2 and R3.