Alarm Dialer Circuit
This circuit dials a stored DTMF tone sequence from EPROM when a control line is taken to 0 V. ICl is a Schmitt trigger oscillator, running at around 2 Hz. It ...
Emergency Telephone Dialer Circuit
This system will alert you or anyone chosen by automatically dialing a programmed phone number. This is accomplished by monitoring an open- loop or closed-loop...
Alternate Tone Alarm Circuit
A two-tone generator that is alternately switched ON provides a high/low output as might be heard from a traffic vehicle like a police car or ambulance. IC1, C...
Low Level Sounder Circuit
This is a simple low-level noise maker that`s ideally suited to certain alarm applications. When the sounder is located in another part of the building, the so...
Dual Tone Sounder Circuit
An outside horn-type speaker works best with the circuit. However, such devices require a great deal of power, so this sounder should only be used in alarm cir...
Spaceship Alarm Circuit
By using two 555 timers this circuit produces a low frequency tone that rises to a high frequency tone in a little over 1 second. Then the sound stops for abou...
1000Hz Pulsed Tone Alarm Circuit
IC1 generates a pulse that modulates the 1000-Hz tone generated by IC2....
Siren Alarm Circuit
The ramp voltage from the low frequency oscillator 1C1 modulates IC2 thereby producing a rising and falling tone like the siren ...
Proximity Alarm Ii Circuit
A CMOS logic gate is used to make up this circuit. When an object is near the antenna, the change in oscillator output is detected by 1)1 and 1)2 and amplified...
Proximity Alarm I Circuit
IC1 contains several oscillators and an amplifier. The low-frequency audio-signal oscillator is used to supply an input to the amplifier. That signal is the au...
Simple Flood Alarm Circuit
A common collector amplifier drives a 2N3904 switch to sound alarm BZ1. The wire leads to water sensor or sump pit, level switch, etc....
Audio Memo Alert Circuit
This device prevents paper notes and memos from being overlooked. A paper note placed between two fingers made of a conducting material (metal or conductive pl...
Ac Wiring Locator Circuit
The tester consists of a rectifier circuit and a multivibrator circuit. The ac voltage is half-wave rectified by diode D1 and stored in capacitor CI. Resistor ...
Flash Signal Alarm Circuit
This circuit is useful if you need a low-energy flashing alarm. The 200 to 400-dc supply should have enough internal resistance to charge the 0.5 capacitor be...
Twin Bell Circuit Circuit
It is often desirable for a single doorbell to be operated by two buttons, for instance, one at the front door and the other at the back door. The additional b...
Digital Entry Lock Circuit
A block pinout diagram of the LS7220 keyless-lock IC is shown. The keypad must provide each key with a contact to a common connection. In this case, the common...
Bug Detector Circuit
The circuit, built around a single integrated circuit (Ul, an MC3403P quad op amp), three transistors (Q1-Q3), and a few support components,.receives its input...
6 Digit Coded Ac Power Switch Circuit
This switch uses four CD4013 BE dual flip-flops, an inverter, and an optoisolator to drive a triac. The circuit can switch 25-A ac load current. A standard 4x3...
Pc Password Protection Circuit
With this circuit, a PC will be protected, requiring a password to boot. After three times, the computer will have to have a cold reboot and the password tried...
Carrier-Current Baby-Alert Receiver Circuit
The baby-alert receiver is comprised of three transistors: Q2, which is configured as a high-gain linear amplifier; Q3, which serves as both an amplifier and d...