This article shows you how to build a dimmer switch for your light bulb that fades in and out smoothly.
When you turn it on, the light will slowly get brighter, and when you turn it off, it will slowly dim down before turning off completely.
This is a nice effect for bedrooms or living rooms.
Circuit Working:
Parts List:
| Category | Description | Quantity | Notes |
|---|---|---|---|
| Resistors | 10k | 1 | 1/4 watt |
| 68k | 1 | 1/4 watt | |
| 1M | 1 | 1/4 watt | |
| 22k | 1 | 1/4 watt | |
| 470Ω | 1 | 1/4 watt | |
| Potentiometer | 500k | 1 | |
| 22k | 1 | ||
| Capacitors | PPC 0.1μF 400V | 2 | |
| Electrolytic | 1000μF 16V | 1 | Note C1 100μF mistakenly shown in diagram) |
| Semiconductors | Transistor BC547 | 1 | |
| Diac DB3 | 1 | ||
| Triac BT136 | 1 | ||
| LED (in light-proof box) | 1 | ||
| LDR (in light-proof box) | 1 | ||
| Others | Switch ON/OFF | 1 | |
| Diode 1N4148 | 1 | ||
| Bulb 220V | 1 |
This automatic light dimmer circuit enables the gradual control of a lighting system for both turning on and off.
when switch S1 is activated, capacitor C1 undergoes a gradual charging process.
Once the voltage across C1 reaches 0.6 transistor T1 initiates conduction, causing the LED to illuminate.
With further increase in capacitor voltage T1 conducts more current resulting in a brighter LED illumination.
If the LED is lit the reduced resistance of the LDR causes the triac to periodically conduct earlier.
This technique facilitates a gradual illumination of the lighting system.
Conversely, when switch S1 is turned off opened the LED does not immediately extinguish due to the slow discharge of the capacitor voltage at the base of T1.
The LED gradually dims until it ultimately turns off allowing for a fading out effect in the lighting.
Potentiometer P2 should be adjusted to ensure that the anode voltage of D1 is approximately 0.7V.
This configuration ensures that the capacitor voltage remains around 0.5V during standby indicating lights off.
Formula:
The time constant in an RC (resistor capacitor) circuit above is calculated using the RC time delay formula.
When charging or discharging a capacitor, the time constant 𝜏τ indicates how long it will take for the voltage across the capacitor to reach around 63.2% of its ultimate value.
RC Time Constant Formula
The following formula may be used to get the RC time constant, 𝜏:
τ = R * C
where:
- τ is the time constant in seconds.
- R is the resistance in the circuit in ohms.
- C is the capacitance in the circuit in farads.
One may approximate the time delay T that an RC circuit provides for charging or discharging by multiplying the time constant (τ) by a value that corresponds to the percentage of the final voltage obtained.
In general, it is provided for 63.2% (which corresponds to 1−1/e where, e is the base of the natural logarithm).
For charging (from 0% to 63.2% of final voltage):
Tcharge = 0.693 * τ
For discharging (from 100% to 36.8% of final voltage):
Tdischarge = 0.693 * τ
The natural logarithm of 2 (ln(2), which is 0.693 in this case, derives from the typical exponential decay or rise of the capacitor voltage in an RC circuit.
How to Build:
Building the automatic light dimmer circuit described involves assembling the necessary components and connecting them according to the provided circuit diagram.
Connect Transistor T1:
- Connect the emitter of T1 to the ground.
- Connect the collector of T1 to one leg of the LED.
Connect Triac:
- Connect the anode of the triac to the collector of T1.
- Connect the cathode of the triac to the positive side of the power source.
Connect LED:
- Connect the other leg of the LED to the ground.
Connect LDR:
- Connect one end of the LDR to the base of T1.
- Connect the other end of the LDR to the cathode of D1.
- Connect the anode of D1 to the junction of the SCR anode and T1 collector.
Connect Capacitor C1:
- Connect one leg of C1 to the base of T1.
- Connect the other leg of C1 to the anode of D1.
Connect Resistor R1:
- Connect one end of R1 to the base of T1.
- Connect the other end of R1 to the anode of D1.
Connect Potentiometer P2:
- Connect one end of P2 to the junction of T1 base, C1 and R1.
- Connect the other end of P2 to the ground.
Connect Switch S1:
- Connect one end of S1 to the junction of T1 base, C1, R1 and P2.
- Connect the other end of S1 to the positive side of the power source.
Adjustments:
- Adjust Potentiometer P2 to set the anode voltage of D1 to about 0.7V.
- Ensure that the values of the components resistor, capacitor, transistor are chosen appropriately based on your specific requirements and the characteristics of the components used.
Power:
Connect the circuit to a suitable power source, and when the switch S1 is closed the circuit should operate as described gradually turning on the LED.
When the switch S1 is opened the LED should dim slowly before turning off.
Note:
Remember to double check the connections and component values to avoid any issues.
If you are not familiar with electronic circuits consider seeking assistance from someone with experience in electronics or consulting a professional.
Conclusion:
The specific design and components used may vary depending on the desired application and the level of control required.
As with any electronic circuit, it is important to follow a detailed circuit diagram and ensure that the components chosen are suitable for the intended purpose.
Additionally, proper safety precautions should be taken when working with electrical circuits.
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