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. I`ve used a 12-volt supply in the drawing - but the circuit will work at anything from 5 to 15-volts. All you need do is select a siren,
Click here to download the full size of the above Circuit.
buzzer, and relay to suit the voltage you`re using. When you switch the alarm on - the buzzer will sound eight times. This is the exit delay. Before the end of the eighth beep - you can leave the building without activating the alarm. R6 controls the length and speed of the beeps. It can be adjusted to give an exit delay of anything from about ten seconds - up to about a minute. After the eighth beep - the buzzer should stop sounding. This confirms that the loop has been restored within the time allowed. If the buzzer does not stop - but changes instead to a continuous beep - the loop is open and the building isn`t secure. When this happens - you should switch off the alarm - and check for open doors, windows etc. When you return and open the door - the buzzer will sound again - and the entry delay will start. The entry delay is the same length as the exit delay. But to distinguish it from the exit delay - the buzzer will sound continuously. If the buzzer is sounding continuously - the alarm has been activated - and the entry delay has begun. If you don`t switch the alarm off before the entry delay expires - the siren will sound. The siren will sound only once. Just as R6 sets the lengths of the exit and entry delays - it also sets the siren cutoff time. The siren cut-off delay is 30 times the length of the exit delay. With the exit delay set at 30-seconds - the siren will sound for about 15-minutes. Then it will switch...
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.....
characters left: