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Series Parallel Loop Alarm Circuit – Circuit Schematic
Series Parallel Loop Alarm Circuit
Two SCRs are used with two sensor loops. One loop uses series switches, the other loop parallel switches. When a switch actuation occurs, the SCR triggers....
Multi Loop Parallel Alarm Circuit – Circuit Schematic
Multi Loop Parallel Alarm Circuit
This alarm has status LEDs connected across each inverter output to indicate the status of its associated sensor. S8 is used to monitor the switches via the LE...
High-Power Alarm Driver Circuit – Circuit Schematic
High-Power Alarm Driver Circuit
In this circuit, a low-powered SCR is used to trigger a liigher powered SCR. When a switch is opening (S2, S3, S4) or closing (S5, S6, S7), either SCR1 or SCR2...
Answering Machine Beeper – Circuit Schematic
Answering Machine Beeper
When the light on the answering machine blinks, the resistance of photoresistor Rl charges, triggers the timer (Ul...
Phone Message Flasher – Circuit Schematic
Phone Message Flasher
This circuit flashes an LED to indicate that your phone rang during your absence. A differential amplifier with hyste...
Sound-Operated Switch – Circuit Schematic
Sound-Operated Switch
This sound-operated switch will sense the ring of the phone and translate this to a lamp that will go on and off. The...
Compressor Protector – Circuit Schematic
Compressor Protector
This circuit monitors the power-line (ac) voltage. When a power failure occurs, on restoration of power, the circuit a...
Wireless Ir Security System – Circuit Schematic
Wireless Ir Security System
This system contains an IR transmitter, an IR receiver/RF transmitter, and an RF receiver/alert beeper. Two IR ...
Mains Failure Indicator – Circuit Schematic
Mains Failure Indicator
When the mains voltage is present at the input terminals, the transistor in the optocoupler is on, T1 is off, and s...
Water-Leak Alarm – Circuit Schematic
Water-Leak Alarm
If you choose to make your own moisture sensor,; this foil pattern should come in handy. A sensor connected to J1 causes S...
Flood Alarm – Circuit Schematic
Flood Alarm
Using a few bipolar transistors, this circuit acts as a flood alarm. When liquid touches the probes, leakage current biases Ql,...
Strobe Alarm – Circuit Schematic
Strobe Alarm
This strobe gives a visual indication of a sensor input. The input signal causes Ul, a light dependent resistor, to chaijge CI...
Digital Entry Lock – Circuit Schematic
Digital Entry Lock
A keypad enters a four-digit access code, which is programmed via jumpers on a 24-pin plug-in header and socket. Ul is a...
Line-Operated Smoke Detector – Circuit Schematic
Line-Operated Smoke Detector
Using an ionization chamber and a high-impedance (CA3130) op amp, the presence of smoke will cause the CA3130 ...
Printer Error Alarm – Circuit Schematic
Printer Error Alarm
When a printer is shut down, this alarm sounds an alarm. The input can be either a high-to-low or low-to-high transitio...
Home Security System – Circuit Schematic
Home Security System
This alarm circuit activates when SI through S5 are activated. This lights LED1 and activates Ql via IC1C and IC1D. RY...
Simple Burglar Alarm – Circuit Schematic
Simple Burglar Alarm
Using one IC and a driver transistor, this simple alarm uses either NO or NC sensors. When a sensor operates, the inpu...
Burglar Alarm With Timed Shutoff – Circuit Schematic
Burglar Alarm With Timed Shutoff
When SI (sensor) is closed, power is applied to U2, a dual timer. After a time determined by C2, CI is ene...
Single-Ic Alarm – Circuit Schematic
Single-Ic Alarm
With a single IC, you can build a simple, reliable auto burglar alarm or a similar alarm. See (a) for the timing informatio...
Automatic Turn-Off Alarm With Delay – Circuit Schematic
Automatic Turn-Off Alarm With Delay
In this circuit, IC1A and IC1B act as a monostable multivibrator. Any input from the sensors SI through...