# How do I connect an avalanche photodiode to an Arduino Uno?

I understand that there was one other question regarding avalanche photodiodes, however I am looking more for connecting my APD to a microcontroller (Arduino).

https://www.edmundoptics.com/testing-detection/detectors/avalanche-photodiodes/

As I understand, the middle leg is the "ground" to the casing, while the other two are anode/cathode. However, since my Arduino's ground and anode are technically the same, how should I connect them? Or should the ground be wired to something else entirely?

## 2 Answers

I hope you are very ESD aware at those $prices. Some plastic 2 pin narrow band ones at Digikey are only$30 but obviously low SNR with no cooling option.

The pin 4 centre pin helps reduce noise but increases stray capacitance loading.

PIN 4 is not connected internally to PIN 1 or 3.
Pin 2 also may be the metal case.

• Would I have major issues using this cascade photodiode? I just used whatever was lying around my lab, I chose it because I needed someone that was able to discern extremely low intensities at sub microsecond response times. I was reading about phototransistors but I wasn't sure if they'd be suitable. – Tyler Dirndl Apr 10 '18 at 4:25
• 5mm Photodiodes are excellent for 0.5A/W but for APD's you can get 50A/W and if above above BDV, can latch to trigger steady DC after a single photon but active cooling. Both require low match impedance transmission lines for optimal bandwidth. So use a PD with a good TIA rather than PT's which have uncontrolled hFE and lower BW but higher gain. Did I answer your question? – Sunnyskyguy EE75 Apr 10 '18 at 14:50
• I will have to look more into it, might just go with a small array of cheaper PDs instead of this one just in case. Thank you so much for your insight! – Tyler Dirndl Apr 11 '18 at 14:18

You can connect case pin to the ground and that is a safer side too. Normally you will connect the anode of the photodiode to the analog pin of Arduino and cathode to the ground. Cathode and case pin shares the same ground.

When you see the image 3rd pin is the case pin which has no connection with the photodiode. Also, since it is a low light level measurement it is suggested that using a transimpedance amplifier in a circuit is a good choice.

Based on the bandwidth, noise and sensitivity and other important factors, you should choose an appropriate photodiode for this photodiode.

• I will shop around more and look for much cheaper alternatives, thank you so much! – Tyler Dirndl Apr 11 '18 at 14:19