- SCR - BR 131/ BT 169 (1)
- TRANSISTOR C828 / C945 (2)
- RESISTOR 200K PRESET (1), 200K PRESET (1) , 1K (1) , 560 OHM (2)
- LDR (1)
- LED (2)
The circuit uses two c828 transistors, a BT 131 SCR, a 200K PRESET CONTROL, a 1K resistor, two 560 ohm resistors, a light-sensitive LDR, two red LEDs and a buzzer. When 4.5 V power is supplied to the circuit, the current control impedance with the red LED can be reduced.
Power the circuit by turning on the 200k PRESET CONTROL, illuminating the LDR and setting the second red LED bulb and horn to work. If the circuit is set up correctly, they will be active when the light is on, and they should continue to be active even when the light is turned off.
The 200K PRESET CONTROL can be replaced with a 100K PRESET CONTROL, the C828 transistor can be replaced with any NPN transistor such as the C945, and the BT 131 SCR device can be replaced with a SCR such as the BT169. The circuit can be made without welding using a project board. Then temperature-sensitive devices such as transistors can be protected.
Circuit activation
This is a light sensitive circuit. The LDR device here has a higher resistance in the dark and a lower resistance in the light. Accordingly, as soon as the light falls on this circuit, the resistance of the LDR decreases and a positive potential is received through the base terminal of the transistor. Then the transistor is activated. A current then flows through terminals C and E of the transistor and part of that current reaches the SCR device through terminal G. The SCR device then activates and a current begins to flow from the anode to the cathode. That is, the second red LED is lit. The buzzer is active. To stop them, the electricity must be stopped and restored.
Bug fix.
If the circuit does not work, turn off the power. If the terminals of the transistor or SCR device are not connected properly, it is not advisable to continue to supply power. Start at low power first. Make one change at a time. Be extra careful when welding.
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