Arduino Leonardo:
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5V -------------------> 5V (Geiger Counter)
GND -------------------> GND (Geiger Counter)
D2 -------------------> VIN (Geiger Counter)
5V (or 3.3V) -------------------> VCC (Dimmer)
GND -------------------> GND (Dimmer)
D7 -------------------> Z-C (Dimmer)
D12 -------------------> PSM (Dimmer)
RobotDyn Dimmer:
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IN -------------------> AC Live Input
N -------------------> AC Neutral Input
OUT -------------------> AC Live Output (to Lamp)