Micro loop alarm circuit diagram design

The structure is simple, the operation is reliable, the power consumption is very small, and most importantly, the size is small. I started with CMOS logic gates but was soon forced to abandon the (too complex) concept after several unsuccessful attempts. Then it dawned on me that a simple transistor switch might do the job, and I was right.

As you can clearly see from the schematic, the circuit is completely original and consists of two identical transistor switches. Each has its own alarm LED and they're coupled with a neat 82dB buzzer. Two 1N4148 diodes are used to prevent a signal from one sensor from triggering both LEDs. The sensors used are wire loops or reed switches that are normally closed, or even a combination of the two. , for example, you could tie a wire loop to your suitcase and place it on a reed switch for your hotel room door.

Since the purpose of this small alarm clock is to always keep the arms stretched forward, there is no provision for automatic shutdown after a certain period of time. The buzzer will sound until you turn the entire circuit off or cycle the wire back to the jumper. There are also the same two LEDs, indicating their own areas.

Buildings are not important and there are no traps for newbies. The two 100N capacitors are not really necessary, I just included them to make sure there was no noise interference coming from the long wire loops . Transistor, you can use any NPN general audio amplifier/switch (107/108/109 BC, 237/238 BC, 2N2222, 2N3904...). PERF board to assemble the circuit. Together with the buzzer and a 9V battery, it should easily fit in a pocket-sized plastic box smaller than a pack of cigarettes. A new battery should be enough for several weeks of continuous operation.