This post shows you how to build a remote control circuit you can turn on with a flashlight.
It uses a light sensor made with a transistor and a special light detector LDR to pick up the light from the flashlight.
We will show you how to build it and how it works step by step.
What is a Flashlight Activated Remote Control:
A Flashlight Activated Remote Control is a device that allows you to control electronic appliances or devices using a flashlight or any other light source.
The concept is based on the principle of light dependent devices typically utilizing a light sensor or photodiode to detect changes in light intensity.
When the flashlight is directed towards the sensor it triggers specific actions in the remote control such as sending signals to control a TV, stereo, or other electronic devices.
Circuit Operation:
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 | |
| Other | Relay 12V | 1 |
The heart of the circuit is Transistor BC557 which along with the LDR and associated components, forms the light sensor stage.
The LDR is strategically connected across the base of the transistor and the negative supply.
When light falls on the LDR it provides the necessary base bias to BC557 causing it to conduct.
As BC557 conducts, the high potential at pin 14 of IC1 is pulled to logic high leading to a change in the state of the IC.
This alteration in state, in turn activates or deactivates the relay providing a toggle action to the connected load.
This state change persists until the LDR is illuminated again by a flashlight.
To ensure optimal performance the LDR is housed within an opaque pipe approximately one inch in length.
This design prevents ambient light from reaching the LDR.
The pipe should be positioned at an angle that facilitates easy focusing of the light beam onto the LDR.
Formula:
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
Construction Details:
Building the flashlight activated remote control circuit:
- Set up a PCB and ensure it is powered by a suitable power supply.
- Connect the LDR across the base of transistor BC557 and the negative supply.
- Ensure a proper biasing arrangement for BC557 with the LDR.
- Connect IC1 to the circuit, ensuring proper pin connections.
- Pin 14 of IC1 should be connected to the collector of transistor T3.
- Connect the relay to the output of IC1 to enable the toggling action.
- Ensure that the relay is capable of handling the load requirements.
- Place the LDR inside an opaque pipe with a length of about one inch.
- Orient the pipe at an angle that facilitates easy focusing of the light beam onto the LDR.
- Integrate capacitor 0.22µF into the circuit to prevent the system from responding to accidental spurious light beams.
- Connect the circuit to the power supply.
- Ensure the power supply voltage is within the specified operating range for the components.
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:
- Fine tune the circuit as needed for optimal performance.
- Check the angle and positioning of the opaque pipe to enhance light focusing.
Finalize the Circuit:
- Once satisfied with the performance finalize the circuit on a suitable platform or PCB for a more permanent setup.
Caution:
Remember to use appropriate resistor values and verify the specifications of the components used.
It is important to refer to the datasheets of specific components for detailed information.
Additionally, safety precautions should be followed while working with electronic circuits and components.
Conclusion
By following these construction details and incorporating the specified components, you can build a reliable light activated remote control circuit with the flexibility to be triggered by either a flashlight for precise control.