Posted on Feb 5, 2014

When button S12 (#) is pressed, a positive voltage fed through R1 appears at the base of transistor Q1, turning it on. When Q1 is conducting, pin 1 of U1 is brought to ground (low) or the battery`s egative terminal. With pin 1 low, two things occur: Pin 8 of U1 goes high (+9 volts dc), turning on LED 1-indicating that the circuit has been armed-an

Click here to download the full size of the above Circuit.

d pin 13 goes from high to low. Transistor Q2 requires a low signal or negative voltage on its base in order to conduct. It also needs a positive voltage on its emitter and a negative voltage on the collector. As long as the door switch (S15) remains open (with the door itself closed), Q2`s emitter will not receive the necessary positive voltage. If, however, an unauthorized person opens the door, thus closing switch S15 and placing a positive voltage on the emitter of Q1, the following sequence occurs: 2. As Q2 conducts, a voltage drop is developed across the voltage dividers made upof resistors R5 and R6. With R5 at 10, 000 ohms and R6 at 1000 ohms, approximately one volt appears at the gate of SCR1. That`s enough voltage to trigger the SCR`s gate.

Leave Comment

characters left:

New Circuits



Popular Circuits

7 segment rolling display using pc
Solar Panel Based Charger And Small LED Lamp
High impedance DC voltmeter
Motion Detector with PIR Sensor
Headphone Limiter
Short Range Personal Radar Circuit
DZ-2 CRV-46152 Aircraft Direction Finding Equipment
circuit to test servo motor (pole rotor) of parabolic antenna
SAA1042 stepper motor control circuit
Clamp meter circuit
Two-wire RTD connection circuit diagram XTR108