The post explains a simple circuit using PIR, LDR for making an automatic solar LED lamp which can be used for illuminating your home automatically at sunset, and only in the presence of a human member in the premise.

By SS Kopparthy


Here, in this article, a simple yet useful and improved version of the PIR based automatic home lighting system is discussed. A previous version of this circuit is already discussed and is available here: The major improvement is the static detection of human beings and also it works completely on solar energy unless the battery doesn’t get charged on a rainy day or something.

Circuit Working:

The circuit consists of different stages, where each one performs a specific task to keep the circuit working. The first one is the solar panel, solar charge controller and the battery which together control solar based power supply to the circuit. The same stage decides whether power is to be fed from the battery or from the mains, depending on the battery charge and voltage.

Circuit Diagram

A 8550 PNP transistor is used here in the solar charge controller to decide it is day or night depending on the voltage form the solar panel. This is achieved by feeding the solar panel voltage to the base of the transistor hence holding it off during the day time when the voltage is produces by panel. When the dusk sets in the voltage drops across the transistor and battery voltage gets routed to rest of the circuit.

The next stage is a voltage source switcher that decides whether the circuit should be powered using battery voltage or the AC power source depending on the battery voltage level. A DPDT relay is configured to take care of this switching. Hence, the power to the circuit remains uninterrupted.

The next stage consists of the day/night detector that senses whether it is day or night depending on the sunlight incident on the LDR and it triggers the relay correspondingly. A capacitor C1 is attached at base of the transistor T3 in this stage. That makes sure that a small delay is introduced in the sensing so that sudden changes in the intensity of light does not false trigger the circuit. Output of T3 is fed to the next transistor Q1 which actually triggers the relay.

Final stage consists of a PIR sensor HC-SR501 that produces a high output when it detects the presence of a human being in its vicinity which is fed to the base of the transistor Q2 and immediately it fires the relay and the LED’s connected to it gets lit up. When the human moves away, the light gets turned off automatically using the same mechanism.

Finally, for the circuit to work even when there is static occupancy, the an additional stage consisting of the Hex Schmitt trigger IC and few other components may be used in combination with the existing circuit, but please remember to use a bigger battery and solar panel as per requirement. The circuit can be found here:

List of Components:

Solar panel- 10.2V,400mA, 6Watts,
BATT1- 6V, 4.5Ah battery
R1- 1K
D1, D2, D3, D5, D6- 1N4007
D4, D7- 1N4148
R2- 10K trimpot
R3- 200E
R5, R8, R9- 1K
R6- 10K preset
R7- 10K
T1- 8050
T2, T3, Q1, Q2- BC547
C1- 10
RY1- 5V, DPDT relay
RY2, RY3- 5V, SPDT relay
L1, L2, L3- LED's


After completion of this automatic PIR based solar home lighting circuit assembly, the unit can be housed inside a suitable casing(plastic) and installed the in a safe position protected from weather. The solar panel, LDR needs to be located such that sunlight is incident on them directly.

Here is the video of my prototype showing the static occupancy detection, please note that solar panel is not connected to the circuit in the video as the circuit is indoor and also the circuit for PIR sensor motion is powered externally for the time being.

A Simplified Design can been seen below:

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