# How to listen in on 5V hall sensor signal in machine with Arduino Due?

I am attempting to listen in on a signal from a hall sensor in a machine, but without affecting the existing circuit. The machine documentation states that the sensor outputs 5,4 V when high which I have tested via measurement. This is too much for my Arduino Due, hence I plan to use a level converter.

I have tried to sketch the connections in the attached picture. Can someone confirm that this will work in theory? And what voltage I need to supply HV with on the level converter? Do I need to use another step down converter set at 5,4 volt?

A two resistor voltage divider is all you need Voltage divider - Wikipedia

I tried that in 50/50 ratio using two 165 ohm, but the voltage dropped 1,5V before the divider.

Is that because the resistors are so small? And if so, how do I calculate the minimum size?

Hi.

online calculator.

calculator

Enter input Volts.
You need to enter at least 2 of the others values: for r1 r2 and vout.
Remember, you need to enter for r1 and r2 valid resistor values. Not all values are available.

I did not manage to get something sensible using either voltage divider not level converter.

I don't have an oscilloscope so I decided to take apart an old defective sensor - maybe someone can see what IC it is and how the sensor work?

djerik:
I tried that in 50/50 ratio using two 165 ohm, but the voltage dropped 1,5V before the divider.

Is that because the resistors are so small? And if so, how do I calculate the minimum size?

Most likely. You want analog values or digital input? for analog, use 4.7k or 10k resistors. Or use a 10-20k potentiometer, trim it to divide at 3V your sensor output.

I have not been able to make it work I have therefor acquired an oscilloscope, please see attached log. Yellow is the original signal, green is after the voltage divider. The original signal is around 1V when low and 5V when high. From what I can see, the voltage divider works as intended with a low below 0.5 and a high around 2,2V (I use two 10K resistors for a 50/50 ratio). The results at the arduino are however not as expected, as I get around a factor 10 too many interrupts.

Any ideas are welcome. Could it be jitter?