Alarm Circuits
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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.... -
Have you ever seen the stairs to one of the upper stories in your house turn into a waterfall? Or maybe you ve come home to find your aquarium fish trying to swim across the carpet? For your sake, we hope not, because the consequences are usually fairly.... -
In this fire alarm circuit, a Thermistor works as the heat sensor. When temperature increases, its resistance decreases, and vice versa. At normal temperature, the resistance of the Thermistor (TH1) is approximately kilo-ohms, which reduces to a few ohms as.... -
The IC is a quad 2 input "AND" gate, a CMOS 4081. These gates only produce a HIGH output, when BOTH the inputs are HIGH. When the key wired to `E` is pressed, current through R1 and D1 switches Q5 on. The relay energizes; and Q5 is `latched on` by R8. Thus,.... -
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.... -
The TTY and the detector-transmitter unit are connected to separate phone jacks on the same line. When the ring sensor detects an incoming phone call, it activates the transmitter, which sends an RF signal to the receiver in the pager device. The receiver.... -
The 555 can be almost any type, they are all pin-compatible. Although some CMOS types may not have enough power to drive the transistor, in that case use an ordinary 555. C1`s working voltage should be increased to 25V if you decide to go with a 12V power.... -
This Instructable describes the installation of a SPY5000 two way motorcycle alarm with a Honda 1998 CB250 Nighthawk motorcycle. This Alarm is rat.... -
Hi guys..!!this is my 1st easy cheap n simple instructabel u need following components for laser burglar alarm-1. LDR or photocell 2.printed circui.... -
Learn how to fortify your fortress no matter what the size with this ingenious myriad of a customizable laser grid. Once someone steps through and bre.... -
The switch has been mounted inside the tap of the handlebar. I`ve make the battery holder out of an old flashlight. As you can see in the video in step 1, i`ve put the sireen inside the left end-bar grip and the wires pass under the tape and inside the tube.... -
To increase one`s chances of seeing the northern lights, the uncertainties of existing aurora prediction methods can be bypassed by sensing the light from the aurora directly. The Aurora Alarm is a device which accomplishes this objective through the use of.... -
This is a circuit that will go off once it detects a certain amount of light. Once the light the circuit is exposed to increases to a certain level, a loud buzzer will go off, alerting us to this. So the alarm will not go off when the circuit is exposed to a.... -
This is an alarm circuit which will go off when any motion or movement is detected. Once it detects this motion, the circuit will trigger an alarm buzzer to sound which will remain on until the power is disconnected from the circuit. This alarm circuit`s.... -
This is a circuit that will go off if the circuit detects any sound above a certain threshold. Once the circuit detects sound, the alarm goes off alerting us to this sound. This circuit has extreme use when an area ordinarily should be very quiet and should.... -
This is a circuit where an alarm will go off once the circuit is tilted. Once the circuit is tilted beyond a certain degree, a loud buzzer will go off, alerting us to this. Many different types of electronics have tip-over protection circuits. One such....
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This alarm can be very useful in a room or an area that should normally have no movement at all in it. In a totally still room with no movement, no vibration will be detected and the alarm will not go off. Once the circuit detects a vibration, which could.... -
The main purpose of this design was to obviate a small defect of the very popular Fridge Door Alarm circuit, available on this website since 1999 and built by a lot of hobbyists. Unfortunately, that circuit stops operating when the battery voltage falls.... -
Sometimes the need arises for a simple, gated, pulsed alarm. The circuit shown here employs just four components and a piezo sounder and is unlikely to be out-done for simplicity. While it does not offer the most powerful output, it is likely to be adequate.... -
This circuit is a laser alarm system like the one we see in various movies. It uses a laser pointer beam to secure your valuables and property. Essentially, when the beam gets interrupted by a person, animal or object, the resistance of a photodiode will.... -
This low-cost burglar alarm employs a 12V strobe light and a truck reversing horn as the visible and audible alarm outputs while the alarm itself is a 12V horn relay and some pressure mat switches. This simple approach has the benefit that the alarm.... -
Whenever AC mains supply fails, this circuit alerts you by sounding an alarm. It also provides a backup light to help you find your way to the torch or the generator key in the dark. The circuit is powered directly by a 9V PP3/6F22 compact battery. Pressing.... -
This simple alarm circuit was designed for use in a combined garage and rumpus room. It can be assembled on Veroboard and uses just one IC plus a handful of cheap components. The circuit is based on a straightforward 555 timer circuit (IC1). This is wired as.... -
This circuit uses a thin piezoelectric sensor to sense the vibrations generated by knocking on a surface; eg, a door or table. Basically, it amplifies and processes the signal from the sensor and sounds an alarm for a preset period. In operation, the.... -
While smoke alarms are quite cheap devices, the cost of 9V batteries quickly exceeds their purchase price. Added to that is the irritation of random beeps from the alarm as the battery reaches the end of its useful life. This circuit allows typical smoke.... -
In normal suburban driving you pass through so many different speed zones that it can be a nuisance having to switch speed settings. The speed display can also be a distraction. This circuit eliminates the display and the need for speed selection. Each time.... -
The LDR is a variable resistor whose resistance decreases with increase in light intensity. When the light falling on an LDR has normal intensity, its Resistance is large enough and the voltage across R is insufficient to trigger the SCR. However, when light.... -
Here is the circuit diagram for simple door bell, you can assemble this circuit inside your room or home where as keep the switch outside your home or room that is easily noticable by the visitors. The working of this circuit is almost similar to my previous.... -
This circuit alarms whenever someone cross the Laser beam transmitted from a LASER. The output of IC TL071 goes high whenever their is no Light(Laser) Ray. This output voltage is further amplified by means of a NPN transistor Q2, which will drive the buzzer....
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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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