Résumé :
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"Multi-Sensor Safety Dev decided to use new technology to upgrade the wireless water alarm system he had constructed nearly a decade ago. While he was at it, he figured he’d create a complete home security system with water alarms, smoke alarms, motion sensors and door sensors. He also added an interface to a Raspberry Pi with the potential for sending remote alerts to cell phones and other devices. Nearly a decade ago, my cellar was flooded in quick succession by a cracked boiler and a leaking hot water tank, so I was inspired to design and build a wireless water alarm. This was based on an interdigital transducer that used the conductance of water as a sensing principle. I used a simple on-off -key transmission protocol on what was then an empty 914MHz radio band. I described this system in my article, “Build an Inexpensive Wireless Water Alarm” (Circuit Cellar 283, February, 2014). This system worked well for many years, but eventually it started to give some false alarms. The false alarms were caused by the gradual use of the radio band by such things as doorbells and automotive remotes. These devices produced signals on that radio band that defeated the simple expedient of my using amplitude detection of a radio signal to trigger an alarm. Since the original circuit was built using a Microchip Technology PIC microcontroller (MCU), I was able to reprogram it to look for a sequence of pulses of a particular width, and this eliminated the false alarms. Although my water sensor was once again working, I decided to take advantage of inexpensive wireless components that were currently available to build a more robust system." (Extrait de Circuit Cellar n°373)
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