Lights and Display Board Circuits

Solar-powered Automatic Lighting Schematic Circuit Diagram

Smart Solar Garden Lighting System

You are likely acquainted with those small solar-powered lighting units flooding DIY stores every summer, sold at incredibly low prices in bulk. While they do work, their electronics and particularly their flimsy housings, designed for utmost cost-effectiveness, have a lifespan directly proportional to their low purchase price. The project outlined here offers a different perspective. It’s designed to complement existing or upcoming garden lighting setups, especially those more potent than the bargain options mentioned before.

Collaborative Operation with Solar-Powered Battery Charger

This project cannot function independently; it must be integrated with the ‘Solar-powered Battery Charger’ project explained elsewhere in this publication. The charger is equipped with a designated connector, facilitating seamless integration with the garden lighting systems detailed in this project. While the charger handles the intelligent battery charging through solar panels, the circuit presented here focuses on controlling the lighting aspect.

Incorporating Smart Sensors and Time Delay

The system features a photocell, utilizing an LDR (light dependent resistor), to gauge ambient light levels. To prevent needless energy drain from the batteries, it incorporates a presence detector, ensuring illumination only when necessary. Moreover, the detector includes a time delay function, enhancing the practicality of the lighting unit in real-world scenarios.

Solar-powered Automatic Lighting Schematic Circuit Diagram

Simplified Circuit Integration

The circuit, designed for use alongside the solar-powered battery charger, boasts simplicity, as evident from the provided schematic diagram. It relies on a single IC, specifically the Microchip 12C671 PIC microcontroller – the same type utilized in the charger, ensuring ease of procurement. Worth mentioning is the IC’s built-in analog-to-digital converter with multiple inputs, a feature utilized effectively in this setup. Power is sourced from the stabilized 5 V supplied by the charger, connected through pins 3 and 4 of the designated connector.

Charger Adaptation and Lighting Control

For seamless integration, a specific alteration in the charger setup is necessary. The jumper between pins 1 and 2 of its connector must be removed when used with the automatic lighting system. This modification enables relay Re2 in the charger to be controlled by the automatic lighting system instead of directly by the charger itself. The load managed by this automatic charger comprises the lamps or other controlled lighting devices. Notably, the battery discharge protection feature is retained. The information from output GP4 of the charger’s 12C671 is conveyed to input GP4 of IC1 via pin 2 of the connector. This input also incorporates an optional override switch S1, allowing manual override to switch off the lighting.

Presence Detector and Light Level Sensing

The presence detector relies on a ready-made module, acknowledging the impracticality of building such a unit from scratch in the present market. Powered at 5 V, the module offers a logic high output upon detecting presence, connected to input GP3. It’s crucial to select a module compatible with the application, ensuring the appropriate supply voltages and detection levels.

Light Level Adjustment and Program Implementation

Ambient light levels are gauged using an LDR linked to the analog input AN2. Adjustable potentiometers are connected to inputs AN1 and AN0. Preset P2 facilitates setting the day/night threshold based on the LDR’s properties and placement, while P1 allows configuring the duration of lighting following presence detection, ranging from a few seconds to approximately ten minutes. The program for the 12C671 PIC can be readily accessed for free download from the Elektor website or the author’s personal site ( Upon appropriate adjustment of P1 and P2, the project functions seamlessly.

Critical Charger Adjustment Preceding Integration

It’s crucial to emphasize that the charger must undergo individual adjustment before integrating it with the automatic lighting system. As detailed in the pertinent article within this Summer Circuits issue. Attempting to connect the two projects prematurely may lead to unexpected interactions, presenting challenges in resolving equations with multiple variables.


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