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Enhanced 5 Digit Alarm Keypad
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. Choose the five keys you want as your code, and connect them to `A, B, C,
Enhanced 4 Digit Alarm Keypad
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. The Alarm is set by pressing a single key. Choose the key you want to use and wire it to `E`. Choose the four keys you want to use to switch the alarm off, and connect them
Multi-Zone Transistor-Based Intruder Alarm
This is a simple transistor-based burglar alarm circuit. Its features include automatic Exit and Entry delays - together with a timed Bell cut-off and Reset. It`s designed to be used with the usual types of normally-closed input devices such as - magnetic-reed contacts - micro switches - foil tape - and PIRs. The basic alarm has an "Exit/Entry" zo
Water Activated Alarm
It 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 emitter and the transistor switches on. A larger current flows in the collector circuit enabling
Water Level Alarm
Car Alarm Arming Horn Beep Canceller
Disconnecting the alarm system from the horn relay will eliminate this, but prevent the horn from sounding in the even of an actual alarm. This circuit serves to silence the arming beepyet maintain the alarm by introducing a small delay into the signal. It sits between the alarm and horn relay. The alarm must provide a constant horn signal for...
Receiver Battery Low Voltage Alarm Circuit
Car Alarm wiring diagrams 2
Wailing Alarm Siren
IC2 is wired as a low frequency astable with a cycle period of about 6 seconds. The slowly varying ramp waveform at C1 is fed to PNP emitter follower Q1, and is then used to frequency modulate alarm generator IC1 via R6. IC1 has a natural center frequency of about 800Hz. Circuit action is such that the alarm output signal starts at a low...
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 temper
Two-Zone Burglar Alarm circuit
This two-zone alarm has automatic exit, entry and siren cut-off timers. It was developed for the Beginner`s Guide To Cmos Timers. So it has a particularly detailed circuit description. There`s an optional One-Time-Only module. It will force the siren to switch off after the first ten minutes - and prevent the alarm from activating a second time..
An Expandable Multi-Zone Modular Burglar Alarm circuit
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. By using the Expansion Modules, you can add as many zones as you require; some or all of which may be the inertia (shock) sensor type..
An Expandable Transistor Based Burglar Alarm circuit
This transistor based alarm features automatic Exit and Entry delays - together with a timed Bell Cut-off and system Reset. Along with the Exit/Entry zone - the basic alarm board has one Instant Zone. This will be adequate in many situations. However - the modular design means that it`s easy to add as many zones as you like to the system....
A Transistor Based Single Zone Alarm circuit
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 input devices (Pressure Mats, Magnetic Reed contacts, Foil Tape, PIRs and Inertia Sensors)..
A Cmos Based Single Zone Alarm circuit
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 devices (Pressure Mats, Magnetic Reed contacts, Foil Tape, PIRs and Inertia-Sensors). If the green LED is not lighting - check for an open window or do
A Simpler Cmos Single Zone Alarm circuit
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 normally-closed input devices such as - magnetic reed contacts - micro switches - foil tape - and PIRs. But it can be Easily Modified to accept normally-open trigg
A Cmos 4060 Burglar Alarm circuit
This is a single zone alarm - with automatic exit, entry and siren cut-off timers. It will accommodate all the usual types of normally-closed input devices - such as magnetic reed contacts, foil tape, PIRs etc. But it`s easy to add a normally-open trigger. When the alarm is activated - the siren will sound for a fixed length of time. Then it...
A Dozen Small Cmos Alarm Circuits circuit
This is a selection of small self-contained alarm circuits. They have a very low standby current; and are suitable for battery operation. Some are triggered by normally-open and normally-closed switches. Some react to changes in light or temperature. The result is a variety of output times and patterns..
A Simple Fire-Door Alarm circuit
This circuit will let you know when something that should be kept closed - has in fact been left open. Attach it to a Fire-Door. It will allow you to pass through the door as usual. However, if it`s left open for more than 30-seconds or so - the buzzer will sound..
An Enhanced Shed / Garage Alarm circuit
This is an enhanced version of the simple Garage/Shed Alarm. The Entry and Exit delays have been increased to about 30-seconds - and I`ve added a timed Siren cut-off and automatic Reset. I`ve also replaced the LED with an entry Buzzer. These enhancements mean that the new version will have a much wider application..
Remote Alarm For Smoke Detector circuit
This alarm circuit was designed to monitor a mains-powered smoke detector located in a shed (which is used to house dog kennels). It provides complete isolation from the mains so that low-voltage (12V) cabling could be run to the alarm circuit which is located inside the house. In operation, the alarm signal (I) from the smoke detector is...
A Cmos Based Vehicle Anti-Theft Alarm circuit
This car alarm 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..
Vehicle Anti-Hijack Alarm No3 circuit
Like the first two Hijack Alarms - if a door is opened while the ignition is switched on - the circuit will trip. And after a few minutes delay - when the thief is at a safe distance - the Siren will sound. But this time the engine does not go on to fail automatically. Instead - it will continue to run until the thief turns off the ignition....
Emergency Light and Alarm circuit
This circuit is permanently plugged into a mains socket and NI-CD batteries are trickle-charged. When a power outage occurs, the lamp automatically illuminates. Instead of illuminating a lamp, an alarm sounder can be chosen. When power supply is restored, the lamp or the alarm is switched-off. A switch provides a "latch-up" function, in order to...
A Transistor Based Motorcycle Alarm circuit
This circuit features a timed output and automatic reset. It can be operated manually using a key-switch or a hidden switch. By adding an external relay, it will set itself automatically - and/or immobilize the machine - every time you turn-off the ignition. It`s easily adapted for a 6-volt system - so it will protect your "Classic Bike"..
A 555 -Timer Based Motorcycle Alarm circuit
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 immobilize the bike, flash the lights etc..
A Cmos Based Motorcycle Alarm circuit
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 immobilize the bike - flash the lights etc. Any number of normally-open switches may be use
Water Alarm Circuit
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 dramatic. With a handful of electronic components, you can at least ensure that you will be...
Fire Alarm Using Thermistor circuit
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 temperature increases beyond 100 C. The circuit uses readily available components and...
Fuse Monitor / Alarm circuit
Surveillance Bug Circuits
Ultrasonic distance finder circuit
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 measured. There are three main categories of distance measurement methods in use: a) By...
Simple Metal detector circuit with CD4030
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 find something potentially valuable, hidden a few centimeters below the soil. So many...
Fully automatic watering circuit for flower pots
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 circuit comes as a solution to this problem. Depending on humidity of the pot at...
Simple deep searching metal detector circuit
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 circuit of this metal detector, it is possible to detect a metal coin in depth of 90 to...
Sub-Harmonic Bass Converter for Electric Guitars
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, such as filtering or distortion. Instead, a frequency division system produces outputs...
Echo Depth Sounding Sonar for Boats
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 calibration of the rope. This arrangement still exists in some yachts. The big...
100W HiFi Audio Amplifier Circuit
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 supply must be symmetrical so that no electrolytic capacitors are needed at the outlet....
Plant-Pot Water Level Indicator Circuit
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. The circuit of the device is shown in Figure 2. The water detection is made from the bottom...
Analogue Sound Preasure dB-Meter Circuit
The best human ear can capture sounds from 20Hz to 20KHz. These limits are known to be the broadest that can exist. Normally the normal limits range from 100Hz to about 13KHz and depend on the age and health of the individual. We for our measurements and to have a good accuracy we will get the limits of 20Hz to 20KHz. A sound to be heard does...
Digital Signal Integrity
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