Voltage Led Probe | Electronic Project Circuits

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4V-220V test led probe

Using inexpensive components, you can fit a simple probe circuit into a pencil-sized enclosure. When both LEDs are on, the probe indicates the presence of an ac voltage; either LED alone indicates the presence and polarity of a dc voltage. The diode-bridge arrangement allows one-way current source R1, R2, Q1, and Q2 to light either LED (or both) when the probe is activated by a test voltage. [...]
Read More Source: http://www.circuitsuggest.com/4-220-v-test-probe.html

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Categories: Meter Tags: electronic test equipment, voltage led probe

Ultra-simple Voltage Probe

Detects 1.8 to 230 Volts DC or AC. This circuit is not a novelty, but it proved so useful, simple and cheap that it is worth building. When the positive (Red) probe is connected to a DC positive voltage and the Black probe to the negative, the Red LED will illuminate. Reversing polarities the Green LED will illuminate. Connecting the probes to an AC source both LEDs will go on. The bulb limits the LEDs current to 40mA @ 220V AC and its filament starts illuminating from about 30V, shining more brightly as voltage increases. Therefore, due to the bulb filament behavior, any voltage in the 1.8 to 230V range can be detected without changing component values.

Please read more at the original source: http://www.redcircuits.com/Page25.htm
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