A darkness detector is a square wave generator interfaced with an LDR (light-dependent resistor). In this project, the 555 Timer IC-based MULTIVIBRATOR Square Wave Generator is created.
Since this circuit is mostly based on LDR concepts, we need to obtain the LDR’s basic information before getting a closer idea of this LDR circuit. An LDR is an element that has a resistance that varies with light intensity. It can be used in circuits of light-sensing.
Hardware Components
The following components are required to make Dark Detector Circuit
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Supply voltage | +5 to +10 V | 1 |
| 2. | IC | NE555 timer | 1 |
| 3. | Resistor | 10K, 22K, 100K | 1, 1, 1 |
| 4. | Variable Resistor | 1M | 1 |
| 5. | Capacitor | 100nF | 1 |
| 6. | Transistor | 2N3906 | 1 |
| 7. | LDR | – | 1 |
| 8. | Speaker | 25Ω | 1 |
555 IC Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of 555 Timer
Dark Detector Circuit
Working Explanation
The diagram of the dark detector warning circuit is shown above. The circuit should look pretty much identical after some observations to the ASTABLE MULTIVIBRATOR since the loop is a MULTIVIBRATOR ASTABLE with just one adjustment. The PIN4 RESET pin achieves this adjustment. This pin is connected to 5V in a regular ASTABLE vibrator. But, since we can produce a pulse in this case, it should not be connected directly with +5V in the absence of light. To reset the IC further and avoid the square wave output in the presence of light, the resistor network given by RESET provides a virtual ground.
The transistor powers the speaker here because the IC-driven speaker is not a good idea. In this case, LEDs should substitute the speaker for an output lighting response. So when the LEDs are set, and the darkness decreases, an emergency backup light will be provided.
There is no need for a PNP transistor, but it can be replaced with an NPN and connected to the pin connections.
Applications and Uses
The Dark Detector is a circuit detecting darkness or light absence. Circuits of the darkness detector like this can be found in devices where light can be triggered as it gets dark.
