Go Down

### Topic: [Solved] Photodiode sensor (Read 417 times)previous topic - next topic

#### himalk

##### Oct 07, 2015, 02:18 pmLast Edit: Oct 08, 2015, 02:59 pm by himalk
Hi all

I have a sensor that uses 4 photodiodes to determine the direction of light on it. 2 photodiodes are for the x axis and 2 for the y axis. In the image attached is the circuit I have managed to trace from the PCB.

I have gathered that pin 2 is a reference pin and pins 1 and 4 are for the two axes.

I've shun light on each of the photodiodes and blocked the others. When light was shun on D6 and covered D5 the voltage across pins 1 and 2 is 0.5V. If D6 is covered and light on D5, the voltage across pins 1 and 2 is -0.5V. The same happens with D7 and D8.

Does anyone have an idea on how to read the voltage into an arduino using single supply opamps.

Thanks

HK

#### Magician

#1
##### Oct 07, 2015, 04:44 pm
You can read the voltage directly by arduino analog input, just put a bias voltage on ref. point 2 by 2 resistors divider (8k & 1k ?) from +5V . I 'd recommend 0.55 as an offset, than negative potential  brings it to 0, and positive to 1.1 consequently. Also, arduino ADC has to be set for internal REF.

#### Archibald

#2
##### Oct 07, 2015, 04:54 pmLast Edit: Oct 07, 2015, 04:59 pm by Archibald
You can read the voltage directly by arduino analog input, just put a bias voltage on ref. point 2 by 2 resistors divider (8k & 1k ?) from +5V . I 'd recommend 0.55 as an offset, than negative potential  brings it to 0, and positive to 1.1 consequently. Also, arduino ADC has to be set for internal REF.
I am assuming from the measurements given in the original post that the sensor is connected to some piece of equipment.  It may be inadvisable to connect the ground of an Arduino to one of the pins of the sensor (unless the Arduino is powered from a floating power supply).  We do not know what voltages may be present on the sensor pins with respect to earth ground.

#### himalk

#3
##### Oct 08, 2015, 02:57 pm
Hi guys

I did try a voltage divider yesterday but it didn't seem to work.