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Voltage Monitor Schematic Circuit Diagram

This voltage monitor circuit is based on an Elektor design with a 555 timer IC in the book 302 Circuits, which uses two LEDs (red and green) to indicate whether the voltage is within range (bad or good). However, in practice, this circuit has some shortcomings because the change in the indicated color when the voltage drops below the threshold often goes unnoticed.

Voltage Monitor Schematic Circuit Diagram

The circuit described here is designed to monitor a 12-V supply voltage (such as the voltage of the electrical system in a car) and signals an Undervoltage situation with a blinking green LED, which is more likely to be noticed. The small red LED also lights up in case of Undervoltage to provide confirmation.

The 556 IC used here contains two 555 timers. One of them detects the switching threshold, and the other provides the blinking function. The threshold voltage for the Undervoltage warning can be set to the desired value with potentiometer P1.

The current consumption of the circuit depends on the type of LED used. If a low current LED is used as the blinking indicator, the value of the series resistor (here 330 ohms) must be increased significantly.

A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat. A potentiometer is a type of position sensor. They are used to measure displacement in any direction. Linear potentiometers linearly measure displacement and rotary potentiometers measure rotational displacement.
A potentiometer is also commonly known as a potmeter or pot. The most common form of potmeter is the single-turn rotary potmeter. This type of pot is often used in audio volume control (logarithmic taper) as well as many other applications. Potentiometers work by varying the position of a sliding contact across a uniform resistance. In a potentiometer, the entire input voltage is applied across the whole length of the resistor, and the output voltage is the voltage drop between the fixed and sliding contact.
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