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ELECTRONICS

Non-Contact AC Voltage Detector with LED and Buzzer

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UPDATED 2026-09-12
TYPECircuit
USE-CASENon Contact Ac Voltage Detector
EXAMPLENon-Contact AC Voltage Detector with LED and Buzzer
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CASE ANALYSIS

Scenario

A handheld non-contact AC voltage detector uses a capacitive antenna to pick up AC field; the signal is amplified by two NPN transistors to trigger an LED and buzzer.

Key decisions

  • Use capacitive coupling from antenna to first transistor base
  • Two-stage NPN common-emitter amplifier for sensitivity
  • LED and buzzer connected in parallel from VCC to collector for low-side switching

When to reuse this

Suitable for battery-powered non-contact voltage testers and educational electronics projects needing a visual and audible alert.

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