Carrier-Current Baby-Alert Transmitter Circuit
The baby-alert transmitter is built around an LM324 quad op amp (Ul), two LMC555CM CMOS oscillator/timers (U2 and U3), and a few support components. The transm...
Burglar Chaser Circuit
The burglar chaser makes a great accessory for any alarm system. It creates brilliant flashes of white light and a loud, irritating sound from a metal horn buz...
Alarm Sounder For Flex Switch Circuit
This is a cross-sectional diagram of a flex switch. They can be used as pushbutton or even position sensors. This schematic diagram shows an oscillator, which ...
Self-Latching Light Alarm With Tone Output Circuit
A decrease in the resistance of the CDS cell when light strikes it activates latch a and b, enabling tone oscillator c and d wliich produces an output of about...
High-Output Pulsed-Tone/Light-Activated Alarm Circuit
This circuit can produce up to 1 W of audio power to drive a speaker or horn. When the CDS cell is struck by light, its resistance decreases thus activating NO...
Precision Light Alarm With Hysteresis Circuit
The TL081 is used as a comparator in a Wheatstone bridge circuit. When the CDS cell resistance decreases due to exposure to light, the output from IC2 cause th...
Dark-Activated Alarm With Pulsed Tone Output Circuit
NOR gates a and b form a low-frequency oscillator that is activated when the CDS cell, under dark conditions, causes NOR gate a to see a logic zero at one inpu...
Precision Light-Activated Alarm Circuit
The light-sensitive CDS cell R8 configured in a bridge circuit with IC1 as a comparator causes ICl`s output to go high when light strikes the CDS cell R8, trig...
Light-Activated Alarm With Latch Circuit
In this circuit, light causes R5 to conduct forward-biasing Ql. R6 sets sensitivity. SCR1 is triggered from the emitter voltage on LQ1, sounding the alarm bell...
Light-Beam Alarm For Intrusion Detection Circuit
When the light beam that falls in the CDS photocell is interrupted, transistor (EN3904) conducts thereby triggering SCR1 (CI06) and activating alarm bell. SI r...
555 Based Alarm Circuit
The alarm circuit has a single 555 oscillator/timer (Ul) performing double duty; serving both in the alarm-trigger circuit arid the entry- delay circuit. In th...
Exit Delay For Burglar Alarms Circuit
Depressing SI charges CI to the supply voltage. This biases Ql on via bias resistors R2 and R3. A voltage is available for the duration of the delay period, to...
Piezoelectric Alarm Circuit
The alarm uses a fixed-frequency piezoelectric buzzer in conjunction with the cadmium-sulfide (CDS) cell and the two-transistor circuit to provide a unique eff...
Heat Or Light Activated Alarm Circuit
The tone generated by a 555 oscillator can be turned on (activated) by heat or light. That causes Ql to conduct transistor W2 (TIP 3055)....
No Doze Alarm Circuit
This circuit sends out a loud tone if the input switch (S2) is not retriggered at preset intervals. ...
Audio Alarm Circuit
In the circuit, U1 amplifies the audio picked up by the condenser microphone. Resistor Rl limits current, while R2 and R3 center the output of the amplifier to...
Warble Alarm Circuit
This circuit uses a 556 to first generate a low frequency square wave, that is modulated to produce two alternate tones of about 400 and 500 Hz. Circuit genera...
Delayed Alarm Circuit
The alarm/sensor circuit shown is built around two SCRs, a transistor, a 4049 hex inverter, and a few support components, all of which combine to form a closed...
Closed-Loop Alarm Circuit
A string of three series-connected, normally closed switches are connected across the gate of an SCR. When one opens, the SCR triggers via Rl, sounding an alar...
Parallel Loop Alarm Circuit
Four parallel switches are used to monitor four positions. When a closure occurs on any switch, SCR1 triggers, which sounds the alarm....