AAA Powered LoRa Mailbox Sensor Goes The Distance

As more of the world’s communication moves into the electronic realm, a casualty has come in the physical mail. Where once each new day might have brought with it a bulging mailbox, today it’s not uncommon for days to pass with not even so much as a bill or a coupon book. For [Eivholt] this presents a problem: he doesn’t want to miss a parcel but most visits to the mailbox are futile. His solution is a LoRa-connected mailbox monitor that sips power from a pair of AAA batteries to the extent that so far it’s run for over two years on a single set.

At its heart is a single board, a Talk2 Whisper Node. This packs a low-power version of the ATmega328 microcontroller alongside a LoRa radio and an efficient power regulator allowing it to draw only 8.70 uA in standby mode, waking up only for extremely short periods to check for mail and report via LoRa to The Things Network. The sensor is simply a microswitch, selected after finding a reed switch problematic to install. Finally an SDR was used to debug the operation of the radio.

The write-up also provides an introduction to extreme low power projects, including some tips on measuring such tiny currents. Even if you have no interest in a mailbox, any tricks that can help maximize power efficiency are always worth taking a look at. Check out the video after the break to see this radio-equipped mailbox in action.

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Putting M5Stack On LoRa And The Things Network

LoRa is the new hotness in low-power, long-range communications. Wanting to let the packets fly, [Xose] was faced with a frequecny problem and ended up developing a Europe-friendly LoRa module for the M5Stack system. The hardware is aimed at getting onto The Things Network, a LoRa based network that provides connectivity for IoT devices. While there was an existing M5Stack module for LoRa, it only supported 433 MHz. Since [Xose] is in Europe, an 868 MHz or 915 MHz radio was needed. To solve this, a custom board was built to connect the HopeRF RFM69 series of modules to the M5Stack.

If you haven’t heard of it before, the M5Stack platform is a stackable development board platform. Like Arduino, you can add functionality by stacking PCBs using a standard header. Unlike Arduino, M5Stack fits in a case nicely and is designed for building devices with user interfaces. For $35, you get an ESP32 based system with WiFi, Bluetooth, a color LCD, battery, buttons, a speaker, and IO connectors.

With the hardware in place, [Xose] 3D printed a custom case to hold the board and added it to the stack. The firmware acts as a monitor for The Things Network, showing live coverage. The final product looks very clean for a prototype, maintaining the finished look of M5Stack.

The firmware, board design, and case design files for the project are all available on Github.