Make project: WLAN alarm contact with battery operation | heise online


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Our alarm circuit reacts to external events: It registers the opening of a window contact or a button as well as the closing. In both cases, it sends a data packet via MQTT on request, which can be evaluated with its own applications. An optional alarm center that is independent of the PC visualizes the incoming signals from various alarm transmitters via LEDs.

The hardware implementation of the alarm circuit is based on three components:

  • a lithium battery of the type CR123A with 3V and a capacity of 1.6 Ah
  • an analog part
  • an ESP8266-12E / F

We use the pin on the ESP8266 CH_PD (Chip power-down) to save massive amounts of electricity. In normal operation, the pin is HIGH, if you pull it to 0V (LOW), the ESP switches off and only consumes a few microamps. The analog electronics and the microcontroller are controlled by simple software. The software is also responsible for the WLAN connection and MQTT communication.

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