Tuesday, September 26, 2023

Simple Automatic Bathroom Light

By S.C. Dwivedi

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An automatic bathroom light Circuit can be made in several ways, depending on your preference and budget. Some of the options make use of either a motion sensor, a smart switch, an occupancy sensor, or a photo sensor.

The simple system proposed here makes use of a small magnet fixed in the bathroom door’s frame and a reed switch with normally open contacts as the sensor on the bathroom door, just opposite the magnet. So, whenever you open the door, the reed switch will move away from the magnet.

Automatic Bathroom Light Connection
Fig.1: Automatic Bathroom Light Connection

Note: Be sure to consult a qualified electrician if you’re not comfortable with electrical work or if you need help with installation. Safety should always be your top priority when working with electricity.

Automatic Bathroom Light Circuit Diagram

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The author’s prototype is shown in Fig. 1 and the circuit diagram is shown in Fig. 2.
The circuit comprises step-down transformer X1, a normally closed type of reed switch, bridge rectifier BR1, transistor BC557 (T1), 5V voltage regulator LM7805 (IC1), a small magnet, op-amp 741 (IC2), decade counter 4017 (IC3), transistor 2N2219 (T2), 5V single changeover relay RL1, and a few other components.

Automatic Bathroom Light Circuit Diagram
Fig. 2: Automatic Bathroom Light Circuit Diagram

The circuit needs 5V DC o work, which can be derived from the 230V AC primary to 9V, 500mA step-down transformer X1. The 9V AC from X1 goes to bridge rectifier BR1 for rectification and is filtered by capacitor C1. The rectified and filtered voltage is regulated to 5V DC by IC LM7805, which is indicated by the glowing LED1.

Automatic Bathroom Light Working

When the bathroom door is closed, the magnet and the reed switch are near each other, reed switch contacts are open, and BC557 transistor T1 does not conduct. Hence voltage at pin 3 of IC2 remains lower than the reference voltage at pin 2 (around half of the supply voltage), output of op-amp IC2 at its pin 1 remains low, and decade counter 4017 (IC3) does not get any clock signal.


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  1. Hello sir,
    I made this circuit at my home and I found that the tranistor T1 (BC557) was not pull down at the collector terminal.
    Can you help me that it is working without Pull down resistor. Because when i was making that circuit without pull down that my relay was chattering (ON and OFF rapidly). After Pull down, it works properly as you mention. I put this circuit also in my bathroom and it works perfectly. Thanks for giving such an excellent circuit idea.


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