This article for Simple Electronic Candle Circuit using LDR is fun and easy project to make fake candle with LED, as it uses LDR to make LED flicker like real flame and turns ON when its dark; also LDR controls the LED.
Furthermore, in bright light the LDR has high resistance so LED stays OFF and when its dark the LDR resistance goes low with current flow and LED turns ON.
Circuit Working:
Parts List:
| Components | Values | Quantity |
|---|---|---|
| Resistors | 1k 1/4 watt | 1 |
| 1M 1/4 watt | 1 | |
| Potentiometer 10k | 1 | |
| Light Dependent Resistor (LDR) Photoresistor | 1 | |
| Semiconductors | IC LM358 | 1 |
| LED yellow 5mm 20mA | 1 |
Main Part of the circuit LM358 IC:
- The circuit uses a special chip called the LM358 IC and this op-amp chip works as a comparator in the circuit.
- Also, it has two op-amps inside one chip and this IC works on wide voltage with 3.3V to 32V and it uses very less power.
Building and Testing:
- After making circuit on breadboard and giving power LED should turn ON in dark.
Light Sensor Tuning:
- LED turn ON/OFF based on light and comparator help control this.
- Use the small VR1 potentiometer to set the light level at which the LED turns ON.
Working in Light:
- When light is strong the LDR resistance is low.
- Voltage at comparators positive input is low and then comparator turns LED OFF.
Working in Dark:
- When at dark LDR resistance becomes high, then voltage at positive input goes up and then comparator sees higher voltage and turns LED ON.
Adjusting Sensitivity:
- Turn the VR1 knob to make LED more or less sensitive to light.
- More turn means LED turns ON in little darkness and less turn means LED turn ON only in full dark.
Testing Sensitivity:
- Adjust the knob to test the LEDs response, at high sensitivity, the LED turns ON even when we place our hand near the LDR and at low sensitivity, the LED turns ON only when we fully cover the LDR.
Formulas:
By using LDR we can make fake candle circuit which looks like real candle flicker, as it changes based on light around LDR.
Voltage Divider Formula:
To find voltage across LDR VLDR use formula:
VLDR = Vcc × RLDR / (RLDR + Rfixed)
where:
- VLDR is the voltage on LDR
- Vcc is the power supply voltage
- RLDR is the resistance of LDR
- Rfixed is the fixed resistor in series with LDR
Resistor for LED Current Limit:
To find resistor for LED RLED use formula:
RLED = (Vcc − Vf) / ILED
where:
- Vf is the LED forward voltage
- ILED wanted LED current e.g. 20mA
This is simple circuit and we can change things like power, flicker speed or sensitivity; so try to simulate before building it and use potentiometer to get nice candle flicker look.
How to Build:
To build a Simple Electronic Candle using LDR follow the below mentioned steps for connections:
- First, collect all parts like shown in circuit diagram.
- Next, connect pin 1 of LM358 IC1 to ground through R1 resistor and LED1.
- After that, connect pin 2 of IC1 to middle leg of pot VR1.
- Now, connect pin 3 of IC1 between R2 resistor and LDR.
- Then connect pin 4 of IC1 to ground and connect pin 8 of IC1 to +12V power.
- Connect R1 and LDR from (+) supply to (−) ground and then VR1 potentiometers top leg connects to +12V, middle leg to IC1 pin 2 and lower leg to ground.
Extra Notes:
- We can control how bright and dark it needs to be for LED to turn ON by adjusting potentiometer VR1 and hence, to make LED flicker like real candle we can add flicker effect circuit.
Conclusion:
Overall, this Simple Electronic Candle Circuit using LDR and IC LM358 as comparator to turn LED ON/OFF by light level.
So change potentiometer to set how dark it needs to be for LED to glow, as it is a simple way to make LED act like a real candle in the dark.
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