In this tutorial, we are going to make two circuits of Light Dark Sensors using CA3140 IC. CA3140 is a BiMOS operational amplifier that has MOSFET input and Bipolar output. The other main component used to make this circuit work is an LDR. LDR or Light Dependent Resistor is an electrical component that works according to the intensity of light falling onto it. It senses the presence of light and its resistance is inversely proportional to its intensity. Its resistance is minimum in light and maximum in dark.
The first circuit is a Light sensor circuit and the second is a dark sensor circuit. You can connect any AC/DC appliance with the relay switch at the output of these circuits to operate them with these sensors.
Hardware Components
The following components are required to make Light Dark Sensor Circuit
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Breadboard | – | 1 |
| 2. | Battery | 9-12V | 1 |
| 3. | Connecting wires | – | 1 |
| 4. | IC | CA3140 | 1 |
| 5. | Diode | 1N4007 | 1 |
| 6. | LDR | – | 1 |
| 7. | Resistors | 10K, 1K, 22K, 470Ω | 1,1,1,1 |
| 8. | Variable resistor | 10K | 1 |
| 9. | Electrolytic Capacitor | 22µF | 1 |
| 10. | Relay | – | 1 |
CA3140 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of CA3140
Light Dark Sensor Circuit
Working Explanation
The operating voltage of this circuit is 9-12V. CA3140 IC is working in a voltage comparator mode in both circuits. In this mode, the IC gives high and low output at pin 6 by comparing the voltage difference between pin 2 and pin 3. To adjust the sensitivity of the circuits we have used a 10K variable resistor in both of them.
The first circuit is a light sensor switch circuit. When light falls onto the LDR its resistance will be minimized and it will allow the current to pass through the circuit and activate the relay switch.
The second circuit is a dark sensor switch circuit. When light falls onto the LDR its resistance will be minimal and all the current is passed to the ground of the circuit and the relay remains switched off. In the dark (or in the presence of a very little amount of light) the LDR’s resistance will be maximum and the current will be passed to the circuit. This will activate the relay switch.
Applications and Uses
- Bedside lamps
- Emergency lights
- Toys
- Porch of house
