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ELECTRONIC COMBINATION LOCK – Circuit Schematic
ELECTRONIC COMBINATION LOCK
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 bro...
ULTRASONIC PEST REPELLER – Circuit Schematic
ULTRASONIC PEST REPELLER
The device emits ultrasonic sound waves that sweep between 65, 000 and 25, 000 hertz. Designed around a 556 dual timer, one half operated as an astable nultivib...
TWO TONE SIREN – Circuit Schematic
TWO TONE SIREN
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POLICE SIREN USES FLASHER – Circuit Schematic
POLICE SIREN USES FLASHER
Low-drain circuit operating from 1. 5-V cell uses National LM3909 flasher ICs to simulate "whooper" sounds of electronic sirens used on some city police cars an...
LOUD BIKE SIREN – Circuit Schematic
LOUD BIKE SIREN
Uses 5558 dual opamp and four general-purpose NPN transistors to generate triangle wave that can be distorted by 10k symmetry control to give either fast or slo...
POLICE SIREN – Circuit Schematic
POLICE SIREN
Circuit used in Dietz siren-light police-car system gives distinctive tones. Position t of S1 produces slow continuous rise and fall. Position 3 produces fast r...
FIRE SIREN USES FLASHER – Circuit Schematic
FIRE SIREN USES FLASHER
Low-drain circuit operating from 1. 5-V cell uses National LM3909 flasher IC to simulate fire-alarm siren. Pressing button produces rapidly rising wail, with to...
10 W AUTO ALARM SIREN – Circuit Schematic
10 W AUTO ALARM SIREN
Generates force field of high-intensity sound inside car, painful enough to discourage thief from entering car after tripping alarm switch by opening door. Circ...
Fire siren – Circuit Schematic
Fire siren
This LM3909 circuit produces a rapidly rising wail upon pressing the button, and a slower "coasting down" sound upon release. If it is desirable to have the ton...
ji1000 car alarm system schematics – Circuit Schematic
ji1000 car alarm system schematics
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12v sensor light – Circuit Schematic
12v sensor light
I wanted to add a security/sensor light near the main doorway that would run of 12 volts. You can buy 12 volt PIR sensors, but these are very expensive at over ...
Emergency warning light LED alarm – Circuit Schematic
Emergency warning light LED alarm
The emergency driver unit consists of a battery charger and electronic circuitry in one compact case. The batteries. Emergency lighting battery protection from ...
Water Level Detector With Alarm – Circuit Schematic
Water Level Detector With Alarm
This is a simple alarm circuit which produces a musical tone when water or some conducting liquid comes in contact with the two sensor wires provided. The circu...
Programmable Home Security Alarm System – Circuit Schematic
Programmable Home Security Alarm System
A low cost high performance programmable home security system using few LDR`s as an input sensors. When above sensor(s) get triggered system may dial the user s...
Pictures Of Doorbell Circuit – Circuit Schematic
Pictures Of Doorbell Circuit
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Mini Tracker – Circuit Schematic
Mini Tracker
A grasshopper is a switch that is ready to go off at any time. A piece of plastic is placed between two switch contacts to keep them apart and connected to cott...
Infinity Bug – Circuit Schematic
Infinity Bug
At this point you whistle into the receiver and the Infinity Bug will pick up the line. The high-gain amplifier in the Infinity Bug will pick up the audio at th...
A LOW-BATTERY ALARM FOR 13.6 VOLT LEAD-ACID BATTERIES – Circuit Schematic
A LOW-BATTERY ALARM FOR 13.6 VOLT LEAD-ACID BATTERIES
[The following circuit is adapted from battery monitors and testers published in The Smith-Kettlewell Technical File (SKTF). The first appearance of this system...
Retriggerable Status Indicator Circuit – Circuit Schematic
Retriggerable Status Indicator Circuit
It is sometimes necessary to monitor a device that generates a relatively short pulse to indicate a change of status. If the duration of the input signal is too...
Drive Safely wth Speed Alarm – Circuit Schematic
Drive Safely wth Speed Alarm
At high speed, visually checking your speedometer to keep under maximum speed can be dangerous. It will be much safer if we put an audio alarm system to give a....