An enjoyable and somewhat basic electronics project is to make a simple electronic candle that uses a Light Dependent Resistor LDR to produce a flickering LED flame that switches on automatically in low light.
To regulate the LED, which serves as the candles flame, the circuit makes use of the LDR variable resistance.
The LED is kept off in brighter situations because the high resistance of the LDR restricts the amount of current that can reach it.
The LED can become active when it becomes dark and the resistance of the LDR decreases, allowing current to pass through it.
Circuit Working:
Parts List:
| Component Type | Description | 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 |
The Core of the Circuit: The LM358 IC
The LM358 integrated circuit IC is a customized chip that is used in this circuit.
An IC used as an operational amplifier, or op amp is the LM358.
The function of the LM358 in this application is comparator.
Actually, there are two operational amplifiers in one integrated circuit.
The voltage range that the LM358 can operate at is rather broad 3.3V to 32V.
Because of its extremely low current demand the LM358 consumes relatively little electricity.
Building and Testing
The LED ought to turn on when the circuit has been assembled on a solderless breadboard and the power supply has been connected.
Fine Tuning the Light Sensor
The circuit regulates the LED depending on light levels using a unique part known as a comparator.
We may fine tune the amount of light required to switch on the LED by using a tiny control dial VR1 pot
How it Operates in Light
A light sensitive resistor LDR provides relatively low resistance when there is an abundance of light.
As a result, the voltage at the comparators ‘positive input’ is lower than the potentiometer set adjustable voltage.
The comparator turns the LED off because of the small voltage differential.
How it Operates in the Dark
The resistance of the LDR greatly rises in the dark.
In comparison to the potentiometer setting this results in a greater voltage signal at the positive input.
The LED glows when the comparator senses a greater voltage differential.
Sensitivity Adjustment
We may modify the circuits sensitivity to variations in light by adjusting the potentiometer.
By twisting the knob more, you may make the LED more sensitive so that it will turn on in even very slight darkness.
If you adjust the knob slightly to make the LED less sensitive, it will only turn on in really dark settings.
Sensitivity testing:
You may play about with the potentiometer to observe how it changes the responsiveness of the LED.
You can keep your hand somewhat away from the LDR and still have the LED turn on by selecting a higher sensitive setting.
To activate the LED on a less sensitive level the LDR must be fully covered.
Formulas:
By employing an LDR, one may design an electronic candle circuit that simulates a candles flickering effect by adjusting the circuit to the ambient light levels that the LDR detects.
The following is a simple formulas that are commonly used to such a circuit:
Equation for Voltage Divider:
One may determine the voltage across the LDR and the resistor VLDR by utilizing:
VLDR = Vcc * RLDR / RLDR+Rfixed
where,
- Voltage across the LDR is equal to VLDR.
- Value of supply voltage is Vcc.
- LDR resistance is equal to RLDR.
- Rfixed is the fixed resistors resistance when connected in series with the LDR
Current Limiting Resistor for LEDs:
Determine the resistor value RLED for current limitation:
RLED = Vcc−Vf / ILED
where,
- Vf is the LEDs forward voltage drop.
- Desired current through the LED e.g. 20mA is represented by ILED.
This circuit serves as a basic example and may be further tailored to meet individual needs, such as power supply voltage, flicker speed, and desired sensitivity.
Before implementing the design, simulations can aid in its validation.
To get the desired candle like effect, adjust potentiometer settings and resistor values.
How to Build:
To build a Simple Electronic Candle using LDR follow the below mentioned steps for connections:
- Gather all the components as shown in above diagram.
- Connect pin 1 of IC1 LM358 to ground through resistor R1 and LED1.
- Connect pin 2 of IC1 LM358 to center leg of pot VR1.
- Connect pin 3 of IC1 LM358 between resistor R2 and LDR.
- Connect pin 4 of IC1 LM358 to ground.
- Connect pin 8 of IC1 LM358 to positive supply of +12V.
- Connect resistor R1 and LDR from positive supply to negative supply.
- Connect pot VR1 upper leg to positive supply, center leg to IC1 LM358 and third leg to ground.
Additional Notes:
- In certain configurations the light intensity at which the LED turns on may be controlled by adjusting the sensitivity of the LDR by the use of a variable resistor.
- To make the LED look more like a genuine candle, you may even add flickering effects.
Conclusion:
To conclude, this LDR electronic candle circuit ingeniously use the LM358 IC comparator chip to control the on and off of an LED in response to light levels.
The circuits sensitivity may be changed by varying a potentiometer allowing us to create a basic automated ‘candle’ that glows in the dark to resemble genuine candles.
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