12 Volt Alarm Power Supply:    (circuit / schematic design added 6/06)

2-input alarm:    (electronic circuit added 2/07)

4 Digit Keypad:    (diagram added 6/03)

5 Zone alarm circuit MIT:    (schematic added 2/07)

5 Zone Alarm Circuit:    (electronic schematic added 8/02)

5 Zone Alarm System:    (electronic design added 6/07)

5 Zone Alarm:    Each zone uses a normally closed contact. se can be micro switches or standard alarm contacts (usually reed switches). Zone 1 is a timed zone which must be used as  entry and exit point of  building. Zones 2 5 are immediate zones, which will trigger  alarm with no delay. Some RF immunity is provided for long wiring runs by  input capacitors, C1-C5. C7 and R14 also form a transient suppresser.  key switch acts as  Set/Unset and Reset switch. For good security this should be ....  (added 09/05)

A CMOS Single Zone Intruder Alarm:    This circuit features automatic Exit and Entry delays - timed bell cut-off - and system reset. It has provision for normally-open and normally-closed switches - and will suit all of the usual input…(added 05/07)

A Simple Electronic Buzzer:    This very simple circuit just uses a couple of resistors, a capacitor and  easily available 555 timer IC. The 555 is setup as an astable multivibrator operating at a frequency of about 1kHz that produces a shrill noise when switched on. The frequency can be changed by varying  10K resistor.   (added 10/06)

A Transistor Based - Single Zone Alarm:    This circuit features automatic Exit and Entry delays - timed bell cut-off - and system reset. It has provision for normally-open and normally-closed switches - and will suit all of the usual input...(added 05/07)

Active IR Motion Detector:    (diagram added 6/03)

Alarm Control Keypad:    (circuit / schematic design added 6/06)

Alarm control keypad:    (diagram added 1/07)

Alarm PSU:    (circuit / schematic design added 6/06)

Alarm System:    (design added 8/03)

Alarm Touched Triggered:    (electronic Circuit diagram added 03/03)

Almost Ultrasonic Motion Sensor:    (diagram added 6/03)

An SCR Based Burglar Alarm:    (electronic design added 6/07)

Anit Theft Motorcycle Alarm:    (schematic added 9/02)

Anti-Theft Alarm for Bikes:    (circuit / schematic design added 6/06)

Anti-Theft Security for Car Audios:    (electronic Circuit / Schematic added 10/04)

Automatic Intruder Alarm:    (electronic design added 6/07)

Automatic Intruder Alarm:    (electronic design added 6/07)

Automatic Intruder Alarm:    This is a simple single-zone burglar alarm circuit. Its features include automatic Exit and Entry delays and a timed Bell/Siren Cut-Off. It's designed to be used with the usual types of...(added 05/07)

Automatic Night Lamp with Morning Alarm:    (electronic Circuit / Schematic added 10/04)

Basic RF Transmitter for PIR Sensors:    (diagram added 6/03)

Battery Low Voltage Beeper:    This circuit provides an audible and visual low voltage warning for 12V battery powered devices. Idle current: 6ma Low Voltage Warning current: 15ma…. (schematic added 9/02)

Beeper:    This circuit produces  sound of a beeper like  one in pagers which produces a "beep-beep" sound. Basically  circuit consists of a 555 timer oscillator which is turned ON and OFF periodically. The first C (left) oscillates at about 1Hz. The second IC is turned ON and OFF by  first IC. The first IC determines how fast  second IC.... (added 10/05)

Big Ben Sound:    This circuit produces  famous Big Ben sound. It produces  "ding dong" sound when switched ON. Basically  circuit alternates between two frequencies which are adjustable. This produces  "ding-dong" sound. The first C (left) oscillates at about 1Hz. The second IC's tone is modulated by  changing voltage at  output of  first IC..... (added 10/05)

Brakelight Flasher:    This is basically a flasher circuit modified to turn on and off a bulb instead of a LED. It uses a 555 timer IC working as an astable multivibrator. The flashing rate can be varied from very fast to a maximum of once in 1.5 sec by varying  preset VR1.  The ON time of  circuit is given by: TON= 0.69xC1x(R1 + VR1) second and  OFF time is: TOFF= 0.69xC1xVR1 second .... (added 10/05)

Broken Charger-Connection Alert:    Detects if a device is not properly connected to its supply.  Suitable for battery chargers, portable appliance supplies etc. (added 3/050

Car Alarm and Immobilizer circiutdb:    This circuit features exit and entry delays, an instant alarm zone, an intermittent siren output and automatic reset. By adding external relays you can immobilize the vehicle and flash the.... (added 2/07)

Car Alarm and Immobilizer:    (electronic design added 6/07)

Car Alarm and Immobilizer:    This circuit features exit and entry delays, an instant alarm zone, an intermittent siren output and automatic reset. By adding external relays you can immobilize  vehicle and flash  lights.....  (added 10/05)

Car Anti Theft Wireless Alarm.:    This FM radio-controlled antift alarm can be used with any vehicle having 6to 12-volt DC supply system. The mini VHF, FM transmitter is fitted in  vehicle at night when it is parked in  car porch or car park. The receiver unit with CXA1019, a single IC-based FM radio module, which is freely available in  market at reasonable rate, is kept ..... (added 10/05)

Car anti theft wireless alarm:    (electronic design added 6/07)

Car Back-up Alarm:    The brake lights of  automobile trigger this circuit on and off.  This save  annoyance of  alarm when it is not needed.  This is an older circuit which was published in Popular Electronics Magazine, but still a good circuit today. (added 6/06)

Car Battery Charger:    (electronic design added 6/07)

Car HiJack Alarm:    (electronic design added 6/07)

CMOS Single Zone Alarm:    (diagram added 6/03)

Cold Activated Switch zen22142:    A simple thermistor triggered cold switch with adjustable threshold.  (added 10/05)

Cold Activated Switch:    The thermistor used has a resistance of 15k at 25 degrees and 45k at 0 degrees celsius. A suitable bead type thermistor is found in the Maplin catalogue. The 100k pot allows this circuit to trigger over a wide range of temperatures. A slight amount of hysteresis is provided by inclusion of the 270k resistor. This prevents relay chatter when temperature is near the switching threshold of this circuit. (added 2/06)

Combination Lock PIC16F84:    (diagram added 6/03)

Combination Lock PIC16F84:    01/15/98 EDN-Design Ideas  /  (added 6/06)  DC/DC converters for use inside the telephone handset require operation from the high-source-impedance phone line. Additionally, the CCITT specifications call for maximum on-hook power consumption of 25 mA. The dc/dc converter in Figure 1 is 70%-efficient at an input power of 25 mA, providing 5V at 3.4 mA. Controlled, low-peak switch current ensures that the ­48V input line experiences no excessive voltage drops during switching.

Combination Lock:    This circuit is very basic to build. To open a the lock which is connected to the K1 Load. you must press each momentary switch in the correct sequence. The sequence used in this circuit is S1,S2,S3,S4. If any of the other switches are pressed the circuit will reset and you will need to start over. Depending on how you wire the switches, you can use any4 switch combination (added 3/03)

Combination Lock-Digital:    (electronic design added 6/07)

Cut Phone Line Detector acake:    Can be used to alarm security system (added 4/02)

Cut Phone Line Detector antoon:    (schematic / circuit added 10/02)

Cut Phone Line Detector:    (electronic design added 6/07)