Alarm Circuits
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Simple construction, reliable operation, very small power consumption, and, most of all, small size. I started with CMOS logic gates, but was soon forced to abandon the concept after a few unsuccessful (and far too complicated) attempts. Then I suddenly.... -
This circuit features automatic Exit and Entry delays and a timed Bell Cut-off. It has provision for both normally-closed and normally-open contacts, and a 24-hour Personal Attack/Tamper zone. It is connected permanently to the 12-volt supply and its.... -
This novel buzzer circuit uses a relay in series with a small audio transformer and speaker. When the switch is pressed, the relay will operate via the transformer primary and closed relay contact. As soon as the relay operates the normally closed contact.... -
Many electronic-control systems have digital outputs that use transistors. One method of improving the security in these outputs is to use an oscillating signal to represent a logic-high state instead of a fixed voltage level (Figure 1). This type of signal,.... -
Using a single cable such as speaker wire or doorbell cable, this circuit can be remotely positioned, for example, at the bottom of a garden or garage, and used to detect all sound in that area. The cable can be buried in a hosepipe or duct and is.... -
This circuit, enclosed in a small plastic box, can be placed into a bag or handbag. A small magnet is placed close to the reed switch and connected to the hand or the clothes of the person carrying the bag by means of a tiny cord. If the bag is snatched.... -
This Design Idea expands on a circuit in a previous one to configure a power-outage detector with a flashing alarm (Figure 1, Reference 1). The circuit plugs into a mains outlet and uses trickle-charged nickel-cadmium batteries. The green-LED monitors the.... -
This simple circuit is sure to have the police beating a path to your door - however, it has the added advantage of alerting you to their presence even before their footsteps fall on the doormat... -
A single zone alarm circuit with entry and exit delay and other facilities. The 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 the usual.... -
The idea behind this snore alarm, is just to rouse the snorer, not the entire household. To wake the sleeper, vibration is used, not an audible alert. The vibration is provided by a small motor housed in a small 35mm film case, which can be placed under the.... -
The Sun-Up Alarm can be used to provide a audible alarm for when the sun comes up or it can be used in a dark area and detect when a light comes on. It can also be used to detect a light beam, headlights etc. The circuit works as follows. The phototransistor.... -
The circuit uses a 555 timer wired as an astable oscillator and powered by the emitter current of the BC109C. Under dry conditions, the transistor will have no bias current and be fully off. As the probes get wet, a small current flows between base and.... -
A circuit that offers visual indication of fluid level in a vessel, with a switchable audible alarm. Example uses would be to monitor the level of water in a bath or cold storage tank... -
This circuit is a simple wire loop alarm that can be used in doorways, hallways, or any other place the tripwire will be broken by intruders. The circuit has a built in siren, but it can be replaced by a relay to drive an external siren, commercial alarm, etc... -
This very simple circuit acts as a high sensitivity capacitive sensor. Lamps and/or Buzzers are operated at half the mains supply voltage when a part of the human body comes in contact with the sensor or approaches it at a close distance. The circuit can be.... -
A multi wire cable tester with a separate LED for each wire. Will show open circuits, short circuits, reversals, earth faults, continuity and all with four IC`s. Designed initially for my intercom, but can be used with alarm wiring, CAT 5 cables and more... -
This tester can be used to check the polarity of any power source, and is therefore very useful when installing automotive equipment, alarm systems or anything else you can think of. Because this circuit is so simple and cheap, even frying one with an over.... -
Sending Morse on a rig without a sidetone is not impossible, but is not particularly pleasant either. This battery-powered monitor has been designed to provide an audible indication of keying for those whose rigs lack a CW sidetone. Its sensor wire is.... -
Many security-alarm systems require the use of a random number. A computer program uses this random number to create a sequence of random numbers to prevent unwanted visitors from gaining entry into a protected facility. You can use a "rolling-code.... -
The circuit shown below is a basic latching circuit consisting of a quad 2-input NAND Gate IC. It is configured such that the flip flop circuit U1A and U1B has both its input held at logic "1". Pin 1 is held at logic "1" by the magnetic contact and pin 6 is.... -
This is the lowest cost dialing alarm on the market and shows what can be done with an 8-pin microcontroller. The complete circuit is shown below. You cannot see all the features of this project by looking at the circuit - most of them are contained in the.... -
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.... -
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... -
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.... -
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.... -
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.... -
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..... -
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.... -
This circuit is designed primarily for the situation where a hijacker forces the driver from the vehicle. If a door is opened while the ignition is switched on, the circuit will trip. After a few minutes delay - when the thief is at a safe distance - the.... -
This circuit features an intermittent siren output and automatic reset. It can be operated manually using a key-switch or a hidden switch; but it can also be wired to set itself automatically when you turn-off the ignition. By adding external relays you can.... -
This circuit features an intermittent siren output and automatic reset. It can be operated manually using a key-switch or a hidden switch; but it can also be wired to set itself automatically when you turn-off the ignition. By adding external relays you can.... -
This is a simple - easy to build - transistor based motorcycle alarm. It`s designed to work at 12-volts. But - if you change the relay for one with a 6-volt coil - it`ll protect your "Classic Bike". The standby current is virtually zero - so it won`t drain....
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This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of.... -
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is.... -
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to.... -
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This.... -
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the.... -
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,.... -
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the.... -
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power.... -
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
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