5 volt 1 watt LED relay module night light circuit using LDR 555 inverter

In this circuit, a five volt one watt LED component turns on when there’s not much light falling on the LDR. A relay module is an electrically controlled mechanical switch, which switches the LED on and off. A 555 timer output determines the high or low switching signal going to the relay module. And the light level on a light dependent resistor voltage divider determines whether the 555 timer output is high or low.

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The LED is wired in series with the normally open position of the relay. The relay I am using is active high. Which means that when there’s a low input, the coil is not energized (normal). The LED is off.

Since the relay module I am using is active high, when there is a high input from the 555 timer output, then the relay coil energizes and the relay switches so that the NO terminal connects to the COM terminal. The LED lights up.

• The 555 timer is wired as an inverter in this circuit. Pins 2 (trigger) and 6 (threshold) are wired together and also to the light dependent resistor (LDR) voltage divider.
  1. More than 2/3 of the supply voltage to pin 6 sets the 555 timer output low. That is the case when a bright enough amount of light falls on the LDR, which is on the high side of the voltage divider.
  2. Less than 1/3 of the supply voltage to pin 2 sets the 555 timer output high. That is the case when there is a low enough amount of light falling on the LDR, as it is on the high side of the voltage divider.

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