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LED?LDR Blinker(BC548)

2014-12-12 19:05  
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This article briefly describes the LED-LDR Blinker (BC548). This principle is easy to understand, but also very practical. Depth understanding of circuit elements, can be more effective to grasp this principle. Do you know the circuit, for example, can understand and buy these components: BC548 .

It normally takes two transistors to build a blinker circuit (in order to make positive feedback possible). However, you can also use a photo-resistor (LDR) that is illuminated by anLED. The feedback takes place here by means of light rays. The circuit is easy to understand. When light falls on theLDR, the current increases. The capacitor then charges, and this increases the base current. This causes the transistor to switch theLEDfully on. The stable ‘on’ state switches to the ‘off ’ state as soon as the capacitor is fully charged. TheLEDis then completely off, the base voltage goes negative and the transistor is cut off.

Figure:1 Circuit diagram

Figure 1 Circuit diagram

The circuit cannot switch back to the ‘on’ state until the capacitor has been discharged via the base resistor. The circuit naturally reacts to external light sources as well. You will have to test it in different light environments to see whether it will work. In any case, it will not work in full sunlight. With an ultra-brightLEDand a very low-resistanceLDR, it might be possible to build a blinker without using a transistor. The combination of theLEDand theLDRwould have to provide the gain that is needed to produce oscillations.



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