Alarm

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 lights. One of the inputs is connected to the vehicle`s existing door-switches. This provides the necessary exit and entry delays. It`s usually sufficient to connect a SINGLE wire to just ONE of the door switches - they`re generally all connected in parallel with the return through the chassis. You can add extra normally-open switches to the door-circuit if you wish; but note that any additional switches will have to be able to carry the current required by your vehicle`s interior light...

The circuit board and switches must be protected from the elements. Dampness or condensation will cause malfunction. Without its terminal blocks, the board is small. Ideally, you should try to find a siren with enough spare space inside to accommodate it. Fit a 1-amp in-line fuse close to the power source. This protects the wiring. Instead of using a key-switch you can use a hidden switch; or you could use the normally closed contacts of a small relay. Wire the relay coil so that it is energized while the ignition is on. Then every time you turn the ignition off, the alarm will set itself...

This FM radio-controlled anti- theft alarm can be used with any vehicle having 6- to 12-volt DC supply system. The mini VHF, FM transmitter is fitted in the vehicle at night when it is parked in the car porch or car park. The receiver unit with CXA1019, a single IC-based FM radio module, which is freely available in the market at reasonable rate, is kept inside. Receiver is tuned to the transmitter`s frequency. When the transmitter is on and the signals are being received by FM radio receiver, no hissing noise is available at the output of receiver. Thus transistor T2 (BC548) does not conduct...

This circuit has been designed to alert the vehicle driver that he has reached the maximum fixed speed limit (i.e. in a motorway). It eliminates the necessity of looking at the tachometer and to be distracted from driving. There is a strict relation between engine`s RPM and vehicle speed, so this device controls RPM, starting to beep and flashing a LED once per second, when maximum fixed speed is reached. Its outstanding feature lies in the fact that no connection is required from circuit to engine...

This circuit can be used to remotely monitor a loudspeaker, alarm, or audio source for presence of an audio waveform. It can also be directly connected across loudspeaker terminals used as a peak indicator. If you need to monitor some audio signal at a location that is either soundproof are too far away to actually hear the signal then you can use a circuit similar to this one. A remote indication that the audio source is active is provided visually, here in the form of a LED. Referring to the above circuit, the 10k preset is a level control which should be adjusted so that when the source ( audio signal or alarm ) is producing the desired amount of noise, the LED lights...

DS1307 is a hardware realtime clock, which works on I2C protocol. Better graphics using the same old fashioned alphanumeric LCD (type HD44780). Icons which shows the status for Alarm ON/OFF state, which gives a nice and cute look to the clock...

Pressing the pushbutton of the transmitter, a sound and/or light alert is activated in the receiver. The system uses no wiring or radio frequencies: the transmitted signal is conveyed into the mains supply line. It can be used at home, in any room from attic to cellar, simply plugging transmitter and receiver in the wall mains sockets. Transmission range can be very good, provided both units are connected to the mains supply within the control of the same light-meter...

This Alarm can be used to protect your property, Inside or Outside. And it can protect a Very Large area such as the complete perimeter of your yard. Be Aware: There are some Possible Drawbacks: Snow or Fog could Block the Beam, Giving a False Alarm...

The alarm will switch off when the 4 keys connected to "A,B,C,D" are pushed in the right order.The circuit works because each gate `Stands` upon its predecessor.If any key other than the correct key is pushed, then gate 1 is knocked out of the stack, and the code entry fails. Pin 1 is held high by R4. This `Enables` gate 1; and when button `A` is pressed, the output at pin 3 will go high. This output does two jobs.It locks itself `ON` through R2 and it `Enables` gate 2, by taking pin 5, high. Now, if `B` is pressed, the output of gate 2, at pin 4 will go high. This output does two jobs. It locks itself `ON` through R3 and it `Enables` gate 3 by taking pin 12 high...

The circuit is easy to use. When you enter the first four digits of your security code - the relay energizes. The 12-volt output moves from the "off" to the "set" terminal - and the green LED lights. At the same time - R12 takes over the job of supplying base current to Q6. In effect - the relay latches itself on...

The circuit is easy to use. When you press "E" - current through D2 & R9 switches Q5 on - and the transistor energizes the relay. The 12-volt output moves from the "off" to the "set" terminal - and the green LED lights. At the same time - R10 takes over the job of supplying base current to Q5. This means that - when you release "E" - the relay will remain energized...

Here is a simple, low-cost quiz table for four game participants. It determines the contestant who first presses the switch (S1 through S4) to answer a question and locks out the remaining three entries. Simultaneously, the respective audio alarm sounds and the bulb glows. The quiz table can be used for more number of contestants simply by adding buzzers, bulbs, MOSFETs and diodes...

Quiz-type game shows are increasingly becoming popular on television these days. In such games, fastest finger first indicators (FFFIs) are used to test the players reaction time. The players designated number is displayed with an audio alarm when the player presses his entry button...

This switch will suit the Modular Burglar Alarm circuit. However, it also has other applications. The Keypad must be the kind with a common terminal and a separate connection for each key. On a 12-key pad, look for 13 terminals. The matrix type with 7 terminals will NOT do...

An inexpensive piezoelectric wafer is used to detect vibration and when the vibration is sufficient a switch is activated...