Building a remote control circuit that can be switched on with a flashlight is explained in this tutorial.
It uses a light sensor which is constructed using a transistor and a specially designed light detector LDR to receive light from the flashlight.
The article provides detailed instructions on how to build a flashlight activated remote control circuit and how to use it.
What is a Flashlight Activated Remote Control:
One may use a flashlight or any other light source to operate electrical appliances or devices using a flashlight activated remote control.
The idea behind this concept is that light dependent devices which usually use a light sensor or photodiode to detect changes in light intensity work on this basis.
Certain functions of the remote control such as transmitting signals to operate a TV, stereo or other electrical equipment are activated when the flashlight is pointed at the sensor.
Circuit Working:
Parts List:
| Component Type | Component Details | Quantity |
|---|---|---|
| Resistors | 10k 1/4 W CFR | 3 |
| 56k 1/4 W CFR | 1 | |
| 2.2M 1/4 W CFR | 1 | |
| Capacitors | Ceramic 0.22µF | 1 |
| Electrolytic 1µF 25V | 2 | |
| Semiconductors | Transistor BC547 | 1 |
| Transistor BC557 | 1 | |
| Diode 1N4148 | 6 | |
| IC 4017 | 1 | |
| LDR (Light Dependent Resistor) | 1 | |
| Relay 12V | 1 |
The foundation of the circuit is the Transistor BC557 which forms the light sensor stage with the LDR and related parts.
The LDR is positioned between the negative supply and the transistors base.
The LDR gives BC557 the required base bias when light strikes it, which triggers it to conduct.
When BC557 conducts IC1s high potential at pin 14 is pushed to logic high changing the ICs state.
As a result of this state change the relay is activated or deactivated giving the connected load a toggle action.
This state shift lasts until a spotlight shines on the LDR once again.
The LDR is enclosed within an opaque pipe that is about an inch long in order to ensure excellent working.
Because of this arrangement ambient light cannot reach the LDR.
It is important to arrange the pipe at an angle that makes it simple to focus the light beam onto the LDR.
Formula:
Below are the formulas for Flashlight Activated Remote Control Circuit:
Circuit Functionality = Transistor T3 + LDR + Associated Components
BC557 Conduction = Illumination of LDR
State Change at pin 14 of IC1 = Relay Activation/Deactivation
Toggle Action = ON and OFF States for Connected Load
How to Build:
For building a flashlight activated remote control circuit follow the below mentioned steps:
- A PCB should be set up and powered by a proper power source.
- The LDR should be connected across the negative supply and the base of transistor BC557.
- Make sure that BC557 has the right biasing setup with the LDR.
- As you connect IC1 to the circuit make sure the pins are connected correctly.
- Transistor T3s collector should be connected to pin 14 of IC1.
- Toggle the operation by connecting the relay to IC1s output.
- Check to see if the relay can manage the required load.
- The LDR should be placed within an opaque pipe that is approximately one inch long.
- The pipe should be angled such that the light beam may be easily focused onto the LDR.
- To stop the system from reacting to unwanted false light beams add a 0.22µF capacitor into the circuit.
- Connect the power source to the circuit.
- A power supply voltage should be within the components recommended working limit.
Test with Light Source:
- Test the circuit by illuminating the LDR with a flashlight.
- Observe the relays activation and deactivation in response to the light source.
Adjustments:
- For best results adjust the circuit as needed.
- To improve light concentrating adjust the opaque pipes location and angle.
Finalize the Circuit:
- Finalize the circuit on the right platform or PCB for a more permanent configuration when you are happy with the performance.
Caution:
Do not forget to check component requirements and use the right resistor values.
The datasheets of each components should be consulted for accurate data.
When dealing with electronic circuits and components safety precautions should also be taken.
Conclusion:
Following these building instructions and adding the required parts will allow you to design an accurate light activated remote control circuit that can be carefully controlled by a flashlight or another source.