Audio Circuit DiagramsLights and Display Board Circuits

Two-way indicator light

The audio signal is applied to the indicator circuit via 1: 1-1: 4 microphone transistor. It determines, which of the two lamps L1 and L2 connected to K1 and K2 respectively is switched on by the relevant silicon-controlled rectifier (SCR).

In the absence of an input signal, both SCRs are switched off. During the positive half period of the mains voltage, the drive voltage is applied to the gate of Th3 Via R2 and iliac Di1. The SCR is then on and switches on L2. When the audio input reaches a certain level. Th1 and Th2 also conduct and switch on L1. At the same time, Th2 removes the drive to Th3 so that this SCR switches off at the next zero crossing of the mains, and lamp L2 goes out. Great care must be taken in the construction of this circuit because potentially fatal mains voltages are present in it during operation. It must, therefore, be built into a well-insulated (man-made fiber) enclosure. The transformer must be a type whose insulation is approved for operation in mains-carrying circuits.

Resistor R2 must be the high-power type. and C1 a 400-V type.
Two-way indicator light Schematic diagram

The resistor is a passive electrical component that creates resistance in the flow of electric current. In almost all electrical networks and electronic circuits, they can be found. The resistance is measured in ohms (Ω). A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit. Resistors can also be used to provide a specific voltage for an active device such as a transistor.
The resistor absorbs the electrical energy in the process where it acts as a hindrance to the flow of electricity by reducing the voltage, and it is dissipated as heat. In today’s world of electronic circuits, heat dissipation is typically a fraction of a watt. Resistors don’t reduce current and voltage instead it opposes the flow of current and produce a drop in voltage across the terminals.

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