LDR Working Project
Automatic light-sensing project using LDR and BC547. Switch LEDs or relays based on ambient light levels for DIY electronics and hobby projects.
LDR BC547 light-sensing project
LDR operating project with BC547 measures the light intensity in the surroundings and automatically switches on LEDs or relays. It is a low-cost, easy learning project of light-sensitive transistor circuits.
LM358 18650 charger DIY
The following circuit LM358 1s2s battery charger, is intended to be a safe charger of either a single-cell (1s) or a dual-cell (2s) 18650 Li-ion battery with the LM358 operational amplifier as the central control component. It offers constant voltage (CV) and constant current (CC) charging phases and has primitive battery protection measures to avoid overcharge, overcurrent and reverse polarity.
This can build a reliable battery charger using the LM358 utility, a component that is well-realised, using this DIY guide to include the parts, the principle of work, the circuit diagram, and instructions. This circuit can be well assembled to provide an efficient and safe way to charge 18650 Li-ion cells in power banks, LED projects, and small portable devices and other electronics requiring batteries.
Components Required for the Circuit
- LM358 operational amplifier IC
- 18650 Li-ion battery (1s or 2s configuration)
- N-channel MOSFET (e.g., IRFZ44N) for load switching
- Resistors (1kΩ–10kΩ for voltage sensing and current control)
- Capacitors (10µF–100µF for smoothing and timing)
- Diodes (Schottky for reverse polarity protection)
- Potentiometer (for current/voltage adjustment)
- Power supply (5V–12V DC input)
- PCB, wires, and connectors
Working Principle of LM358 Battery Charger
Constant Current (CC) Stage
The LM358 monitors battery voltage and regulates charging current through MOSFET control. The battery receives a constant current until it reaches the target voltage.
Constant Voltage (CV) Stage
Once the battery reaches the maximum voltage (4.2V per cell), LM358 maintains voltage and gradually reduces current. Prevents overcharging while topping up the battery.
Battery Protection Features
Reverse polarity protection prevents damage if the battery is inserted incorrectly. Overcurrent and short-circuit protection ensure safety for both the battery and circuit. Optional thermal protection can prevent overheating during charging.
LM358 1s–2s Battery Charger Circuit Diagram
- Connect the LM358 in comparator mode for voltage monitoring.
- Connect the MOSFET in series with the battery's positive terminal to control current.
- Connect resistors for voltage sensing and current limit adjustment.
- Connect capacitors for voltage stabilization.
- Connect the power supply input and output to the battery terminals.
- Optional LEDs can indicate charging status (charging/fully charged).
Step-by-Step DIY Construction Guide
- Place LM358, resistors, capacitors, and MOSFET on a PCB or breadboard.
- Connect voltage sensing resistors to battery terminals.
- Connect MOSFET drain to battery positive, source to load/charging path.
- Adjust potentiometer for desired charging current.
- Connect the power supply to the circuit input.
- Test with a multimeter before connecting the battery.
- Verify LED status indicators if included.
- Secure battery and insulate all exposed connections.
Applications of LM358 Charger Circuit
- Charging single or dual 18650 Li-ion batteries
- DIY power banks
- LED or small portable electronics
- Educational electronics projects
- Battery maintenance and backup systems
Safety Precautions
- Always check battery polarity before connecting.
- Avoid charging damaged or swollen cells.
- Use a fuse for added safety in high-current circuits.
- Do not touch terminals while charging.
- Ensure adequate ventilation for heat dissipation.
Troubleshooting Common Issues
Battery Not Charging
- Verify input voltage and circuit connections.
- Check LM358, MOSFET, and resistor network.
Overheating Battery
- Reduce charging current or check heat dissipation.
- Ensure proper MOSFET rating.
Incorrect Voltage Output
- Check voltage sensing resistor values.
- Verify LM358 and potentiometer adjustment.
Frequently Asked Questions - LDR Working Project:
What is LDR?
Light Dependent Resistor whose resistance changes with light intensity.
Why use BC547?
It acts as a switch to control LEDs or relays based on LDR voltage.
What voltage is required?
Typically 5–12V DC supply.
Can it control a relay?
Yes, with a suitable relay compatible with BC547 current.
Is it beginner-friendly?
Yes, simple and inexpensive for hobbyists and students.
Can sensitivity be adjusted?
Yes, by changing the series resistor with the LDR.
Can it be used for night lamps?
Yes, ideal for automatic night lighting and garden lights.
Do I need additional protection?
Optional diode or fuse for load safety.
Can multiple LEDs be controlled?
Yes, connect them according to transistor current rating.
Is it cost-effective?
Yes, uses inexpensive BC547, resistors, and LDR.
