Sharp GA1A2S100LY

Today I tried to interface a sharp GA1A2S100 photo diode with a arduino. The Sharp GA1A2S100 is a photo diode that detecting ambient light in the visible spectrum. Unlike all the IR sensors.

Vcc to 5V
GND to ground
I0 to analog input

To get a more stable reading use a bypass capacitor of at least 0,01uF as close as possible to the sensor between GND and +5V

Even then I got a floating value with a constant light source.

For a more accurate value a added 10 readings and divided this number by 10. And then it still floats a bit, but not that hard.

Sadly on a quest to find a more extreme low value/ resistance, I burned the sensor with a laser (big green laser)

With the laser I got readings around 600 and in the dark it gave a top of 1003. Without the laser close to a big light source I got readings around 930.
So If you want to use them you should map to value to a more useful value.

To get a more stable reading use a bypass capacitor of at least 0,0uF as close as possible to the sensor between GND and +5V

I think maybe you need a bigger capacitor.

Indeed it should be at least 0,01uF.

I know it's an old post I'm resurrecting however this is the only post that comes up when you google this part so it's advantageous to keep it all in one place.

I have just bought this part because I needed a sensor that could operate at low light levels. I'm waiting for it to arrive so I haven't had a play with it yet however I came here looking to learn how to interface to it.

I believe I know why the original poster had issues. The sensor output is a varying current output and current needs something to pass through in order to be measured and the high impedance of an arduino analog input pin would never allow it to work.

My assumption is that I need to attach some resistors to the output and measure the varying potential across the resistors however the specific details of what the circuit needs to look like escapes me.

The output in the block diagram doesn't look all that different to that of a shunt voltage regulator so I suspect that it needs to be similar to the configuration used for one of those.

Am I on the right track with this or have I missed the mark entirely?

Any help would be appreciated.

Don't you hate it when seconds after you give up and ask you find the answer yourself?

When I was initially looking for a light sensor one of the things to come up was a page for some intersil parts of which some were current output.

I just looked in the datasheets for those intersil parts and the EL7900 has a nice application diagram showing a 10k load resistor to ground and a 110k pullup with a cap in parallel to the load. Awesome problem solved I think :slight_smile: