Interface with hall sensor

Hi everyone,

I want to measure DC current with the CSLA2CD hall effect sensor.

The sensor have a voltage offset of VCC/2. Every amp on the wire adds 33mV.

I will have to add a voltage divider to be in the adc range and a zener for adc pin safety.

What is your opinion about that ? Is it right ?

Thanks in advance

Best regards

Hi,

the max. input for the ADC is 5V, so you can measure up to 2500/32 Amps = 78Amps. A voltage divider will also reduce the resolution of your measuring. A Zehner diode is a good idea, also a restistor of about 1kOhm between sensor output and ADC input, the Z-Diode placed direct to the ADC input. If the range is not big enough, i think it is a better idea to use an opamp to subtract the VCC/2 voltage offset, this gives you up to 156Amps. Above there is a voltage divider or opamp gain below 1 necessary.

Best regards Mike

To suppress the offset, i that the best way to do : http://soundlab.cs.princeton.edu/learning/tutorials/sensors/img47.gif
http://soundlab.cs.princeton.edu/learning/tutorials/sensors/img48.gif

I can also multiply the 33mv / amp to match the whole adc range :
for max 74 amp : Vhall = 2,442 V

If R1/R2 = 2, I will match the 10 adc bits.

V1 is the middle point between vcc and ground with resistor divider.

I can use the AD627 witch is great for instrumentation.

What do you think about that ?

Thanks in advance

Best regards

Why do you want to get rid of the offset in the hardware? Its there so that you can detect negative currents as well as positive currents.

I would read the ADC value into an integer and then subtract 512. A negative number means a negative current. You may need to adjust the 512 to get a zero reading for zero current but thats easier than trying to adjust a voltage to get zero for zero current.

Because I need as much precision as available and a wide range of input values. The adc have 4.89 mV / bit précision. If I use an opamp to match to the adc range, I have a wider range and a better precision (two times better) if I use a instrumentation opamp like ad627.

You can also increase the gain of the Arduino ADC by reducing the voltage on the AREF pin. From a quick look at the datasheet it looks like the minimum you can put on AREF is 1V (probably to keep the resolution above the noise level). This is a free 5x gain already.

Good idea ! You must use all the adc pin for the same purpose. This is not my case ! But it's a good way to do

Thanks