555 timer icElectronic Keys & LocksPower Supplies

On/Off Button Schematic Circuit Diagram

Versatile 555 Timer Circuit

The ubiquitous 555 timer finds its place in virtually every Small Circuits compilation, and in this uncomplicated circuit, we delve a bit deeper into the chip’s capabilities, a topic explored previously in ‘The Eternal 555’ from the July/August 2004 issue. The 555 timer is truly remarkable in terms of its versatility. At Elektor Electronics, we have a special fondness for straightforward circuits involving this IC, exemplified by the one we present here. In this setup, the 555 timer is ingeniously utilized to enable a single push button to control a relay.

Upon a single press, the relay energizes, and with another press, it de-energizes. Moreover, the circuit allows you to specify the initial state of the relay when the power supply is switched on. The overall design, as mentioned before, is elegantly simple. By employing R1 and R2, the threshold and trigger inputs are maintained at half the power supply voltage.

Button Schematic Circuit Diagram

Toggle Operation with 555 Timer:

In this configuration, the output of the 555 timer toggles based on the voltage levels at the threshold and trigger pins. When the voltage at the threshold pin exceeds 2/3 of the power supply voltage, the output goes low. Conversely, if the voltage at the trigger input drops below 1/3 of the power supply voltage, the output goes high. By linking C2 through R3, the output toggles whenever the pushbutton is pressed. For instance, if the output is low, pressing the button causes the trigger input to go low, making the output go high. C1 determines the initial state of the relay upon power application. If the open end of C1 is linked to Vcc, the output is high after power-up. Conversely, connecting C1 to the ground results in a low output at startup.

Essentials of Power Supply Units:

A power supply serves as an electronic circuit converting alternating current (AC) voltage into a stable direct current (DC) voltage. It typically comprises essential components: a transformer, rectifier, filter, and regulator circuits. For computers, a power supply unit (PSU) is crucial, transforming mains AC into regulated low-voltage DC power for internal components. In modern personal computers, switched-mode power supplies are prevalent. Some PSUs incorporate a manual input voltage selector, while others automatically adjust to the main voltage, ensuring seamless compatibility.


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