Tuesday, May 15, 2012

Automatic Emergency Light Circuit Diagram

This is the simple circuit of automatic emergency light. It is called dark dependent circuit. A 555 timer IC and LDR is used for this configuration. When light fall on the LDR, its resistance is decrease and in dark position its resistance is going high. Using these characteristics of LDR, automatic emergency light is made.
LDR is called Light Dependent Resistor. Its resistance is inversely proportional to the falling light on its surface. In dark, its resistance is approximately 7k to 10k. When light fall on its surface, its resistance is decrease to less than 1k. In the circuit, a voltage divider arrangement circuit is used here with LDR and 10K variable resistor.
When light fall on the surface of LDR, the resistance decrease to 1k. So the voltage of the timer pin-6 is greater than 2/3 of +Vcc. For this reason the output pin-3 goes low. The base voltage of transistor BC547 is less than 0.75 volt. The transistor is OFF state. So the light is OFF.
In dark position the LDR resistance increase is high so the voltage of the trigger pin-2 decrease to less than 1/3 of +Vcc. The output pin-3 goes high so the base voltage of the transistor BC547 is greater than 0.75 volt. The transistor is ON state. So the light is ON and it emits light.

Friday, May 4, 2012

Digital Object Counter using LDR and digital IC 7490

This is the simple circuit on Hobby Electronics. In this circuit three modules are used in object counter. 555 timer are used as a monostable mode and astable mode. The other is counter module.

In this circuit 555 timer configured as a monostable mode, is a simple automatic dark sensor circuit that gives output when light falling is blocked on LDR. Pin 3 of monostable circuit has been connected to pin 4 of astable timer. When monostable circuit generates output, astable mode timer starts giving pulses to the counter module. Frequency for counter module is set up using R4, R3 and C2.

7490 acts as a decade counter and 7447 uses the output of 7490 to display numbers on seven segment display. This circuit counts from 0 to 9. You can count 0 to 100 modifying counter module circuit. Just adding few components as well as two counter ic, two display driver and two display. For count 0 to 100, comments on the comments box. You will get complete circuit.
The output will be: If you block light falling on LDR, the number on seven segment display will increase.