Test with a multimeter

Phototransistor

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Now: In the dark, C → E

SHINE LIGHT CircuVanta 6000 counts · auto range DCAUTO•)))HOLDFUSE− HOLD LIGHT OFFV⎓V~Ω•)))FmA⎓ mA400 mACOMVΩ Collector (C) 1 C Emitter (E) 2 E
Pin 1: Collector (C) (C) Pin 2: Emitter (E) (E)

Red probe Not connectedBlack probe Not connected

Hold the probe and drag it to the tip of a leg. Tapping works too: first pick the probe, then the leg.

Set the range to diode test.

Measure step by step

A phototransistor has no base; light acts as the base. In the dark collector-emitter is OL, in strong light it conducts. Measure on the diode range: red probe on the collector, black probe on the emitter.

  1. 1In the dark C → E
  2. 2Under light C → E
  3. 3Under light E → C (reverse)