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Build a Mains-Presence Indicator Concept
Learn safety rules before any mains experiment.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
Concept only
A mains presence indicator is a light that shows whether a mains-powered circuit is live. This page explains the idea. It is not a build guide, because mains voltage can kill and homemade mains circuits are a serious risk.
What a proper indicator does
- It shows a clear light when the supply is present, usually from a neon or LED lamp built into a switch or plug.
- It keeps the mains side electrically separated from anything you can touch.
- It is made and tested to safety standards, with correct spacing and insulation.
What to use instead
Buy approved parts: illuminated switches, indicator plugs and certified non-contact voltage testers. If a project needs mains, use a ready-made certified power supply and keep all your own wiring at low voltage.
REMEMBER
Do not build mains circuits yourself; use certified products.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
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