Simplest Arduino Based Sound / Lightning / Thunder Trigger

This is the simplest sound/lightning trigger based on Arduino.

Parts needed:

1 2N3904
1 1K resistor
1 Piezo buzzer as sound sensor
1 Photodiode BPW21R for lightning trigger
1 Arduino

Instructions:

Step 1: Connect the black wire of Piezo to Gnd pin of Arduino
Step 2: Connect the red wire of Piezo to analog 0 (A0) of Arduino
Step 3: Load the attached sketch file to Arduino
----------------------- at this point, if you clap your hands or snap your finger, watch serial monitor -----------------------------
Step 4: Construct trigger circuit as shown in picture and connect FLASH_PIN to the one defined in sketch
Step 5: Connect a flash to the triggering circuit.
Step 6: Clap your hands or snap your fingers and watch flash goes off.

Step 7: Plug a photodiode with large sensing area, plug the positive terminal into A0 and negative terminal into Gnd
Step 8: Get a flash and set it at lowest output power and watch what happens -- it can be used as lightning trigger

Source code at github: https://github.com/mjkzz/Simplest-Sound-Lightning-Trigger.git