DC or AC Voltage Indicator

Detects 1.8 to 230 Volts DC or AC, Minimum parts counting

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.

Circuit diagram:

DC or AC Voltage Indicator Circuit Diagram

Parts:

P1 = Red Probe
P2 = Black Probe
D1 = 5 or 3mm. Red LED
D2 = 5 or 3mm. Green LED
LP = 1220V 6W Filament Lamp Bulb

Note:

• A two colors LED (Red and Green) can be used in place of D1 & D2.

Source: Red Free Circuit Design

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Simple Ac To Dc Converter Circuit Diagram

This is simple Ac To Dc converter circuit diagram. By coupling two back-to-back diodes in series with an ac power circuit, a voltage of about 1.4 Vpp can be obtained. This voltage is useful for exciting the primary coil of a small transformer. The voltage induced in the secondary coil can then be rectified and used to power solid-state control circuits. The forward-voltage drop of the diodes is inherently constant and stable over a wide range of ac-circuit power variations. 

The resulting voltage developed across the transformer windings is also free from variation that might be caused by changes in the circuit`s current or voltage. In the circuit, a lamp (LMP-1) is connected to the primary ac input line (Ll and L2) through a pair of inverse-parallel-connected power diodes (Dl and D2). As power flows to the lamp, a drop of about 0.7 V is alternatively developed across each of the diodes. 

This voltage feeds the primary of a small transformer (Tl). T1 can be a small 8- to 500- transistor radio output, etc. This will deliver about 11 Vpp across its secondary winding. LMP1 can be a small 120-V lamp of 5 to 25 W, etc.

Ac To Dc Converter Circuit Diagram

Simple Ac To Dc Converter Circuit Diagram

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