Lights and Display Board Circuits

LIGHT SENSITIVE CIRCUIT WITH PHOTOTRANSISTOR SCHEMATIC CIRCUIT DIAGRAM

LIGHT SENSITIVE CIRCUIT WITH PHOTOTRANSISTOR SCHEMATIC CIRCUIT DIAGRAM

When the phototransistor is in the circuit, this element transmits and transmits the BC547 transistor. When the BC547 is switched on, the relay pulls and the lamp illuminates. When the light from the phototransistor is turned off, the relay returns to its original state. With the R1 trimpot, the value of the desired illuminance intensity can be adjusted. As shown, the circuit is sensitive to daylight. If we want this circuit to be only sensitive to infrared rays, we need to cover the lens part of the phototransistor with dark transparent plastic. When we do this, the phototransistor detects only the rays emitted by transmitters with infrared diodes.

For example, let’s think about what to do to set up an alarm in a room. A
the mini-infrared diode transmitter circuit is installed on one side of the room during this operation. The circuit on the wall opposite this transmitter is placed in Figure 3.22. As soon as an object enters between the two circuits, the infrared rays from the phototransistor are cut. This causes the phototransistor to interrupt the BC547 transistor. The BC547 that goes to the cut changes the position of the contacts of the relay and the illuminated lamp goes out.

A phototransistor is a bipolar or unipolar transistor where light can reach the base, creating optically generated carriers. This modulates the base-collector junction resulting in an amplified current through transistor action, which can lead to much greater photosensitivity.
The phototransistor is a semiconductor device that is able to sense light levels and alter the current flowing between the emitter and collector according to the level of light it receives.
BC547 is usually used for current amplifiers, quick switching, and pulse-width modulation (PWM). Therefore, if you need to control the speed of a motor or actuator in some of your projects, you can simply use this transistor to achieve it.10-Sept-2020

BC547 Transistor Features

  • Bi-Polar NPN Transistor
  • DC Current Gain (hFE) is 800 maximum
  • Continuous Collector current (IC) is 100mA
  • Emitter Base Voltage (VBE) is 6V
  • Base Current(IB) is 5mA maximum
  • Available in To-92 Package
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