Today we are come with a unique idea i.e. Photodiode using LED. This project utilized an LED to detect and response on presence and absence of light.
Before starting the description and working of circuit DIY Light Detector Circuit using LED, we would like to describe about few electronics components.
LED: Light emitting diode is a photoelectric device which converts electrical energy into light energy. It is a heavily doped P-N junction diode which under forward bias emits spontaneous radiation.
Photodiode: Photodiode is an optoelectronic device in which current carries are generated by photons through photo excitation i.e., photo conducting by light. A photo diode is a special type P-N junction diode made of photosensitive semiconducting material.
From the above description we came to conclude that LED is for emitting light where photodiode is for detecting light. Both of these semiconductor device work on opposite principle. But here in this project we had use LED as photodiode i.e. detect presence and absence of light. The LED used here is a general purpose 5mm LED and can be any color. But in project DIY photodiode we had used RED color LED because RED LED is more sensitive to ambient light.
Circuit Description of DIY Light Detector Circuit using LED:
The circuit of DIY Light Detector Circuit using LED is designed using a high-performance BIMOS operational amplifier IC CA3140, two NPN general purpose transistor BC547 (T1) and BC337(T2) and few passive electronic components i.e. resistors and capacitor.
Here in this project we are going show how one can use general purpose LED can be used as light emitting as well as light detecting circuit. In the presence of light, the heavily doped P-N junction become forward-biased and voltage of 1V with current of 0.030mA is generated.
According to data sheet of op-amp CA3140 it consists of high impedance MOSFET input and low impedance bi-polar output. The input impedance is about 1.5 tera-ohm which is very high and as a result it changes its output on very low current (in range of few pico-ampere i.e. 10-12 Ampere). Thus, the output of LED is enough to drive this MOSFET used in input of op-amp CA1340.
LED1 (used as photodiode) is connected to op-amp input in reverse bias mode as shown in figure 1 where resistor R1 is a biasing resistor. Resistor R2 is feedback resistor which decide the feedback current of op-amp configured in trans-impedance mode (i.e. current-to-voltage converter).
Operations of DIY Light Detector using LED: When light is exposed to LED1, it generates current which is reverse in nature. The reversing current increase voltage at inverting input pin as a result output become low. This low output of op-amp keeps T1 and T2 in off state and LED2 does not glow.
In dark no current is generated from LED1 thus both the input pin has same voltage. As a result, the output of IC1 become high and drive transistor T1 and T2 in conduction mode and LED2 start to glow.
NOTE: The project DIY Light Detector Circuit using LED posted here can be used as night lamp. In order to do so LED2 replaced with relay in order to control AC load.
PARTS LIST OF DIY LIGHT DETECTOR CIRCUIT USING LED
|Resistors (all ¼-watt, ± 5% Carbon)|
|R1 = 1 MΩ
R2 = 10 MΩ
R3, R4 = 1 KΩ
R5 = 100 Ω
|C1 = 100 µF, 16V|
|IC1 = CA3140
T1 = BC547
T2 = BC337
LED1 = 5mm RED LED
LED2 = 5mm Any color LED
|B1 = 9V Battery|