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Stephen Downward bba51b6712 Added LPF. updated screenshots 5 months ago
Hardware bba51b6712 Added LPF. updated screenshots 5 months ago
.gitignore 80de18873f Added gitignore, proper GPS power 6 months ago
LICENSE.md b847d449b5 first commit 6 months ago
README.md 59df3526a0 Fixed link to image in README 6 months ago

README.md

Smallest APRS transmitter

Board

I designed this in about an hour, with the goal of creating a low power, extremely small APRS transmitter. It measures 4.5x2.4cm, making it the world's smallest, and draws under 20μA in standby, allowing it to run for months or years when asleep.

The tracker features a micro USB port for charging and programming the ATmega32u4, which controls the board. A JST connector allows for any sized 3.7v lithium-ion battery to be attached, allowing for customization between size and battery life. The entire back-side of the PCB is used for the DRA818V transceiver, which is the largest part by far, and provides a modest 0.5W/1W signal to the SMA connector for transmission. It is also the most power-hungry part, drawing 750mA when transmitting at 1 watt, and 400mA when transmitting at 0.5 watts. Because of this, it is important to limit the frequency of transmissions to prevent running the battery flat. The MT3339, the onboard GPS, is both low cost and extremely small. Although it does not have a low-power mode, it draws under 30mA when in use, allowing for it to be safely powered directly from a GPIO pin on the ATmega32u4. The tracker can safely be used while being charged- in fact, there is no way to turn it off without removing the battery. This is thanks to the onboard MCP73831T, which also limits the charging current to 500mA(adjustable by replacing a resistor) and prevents overvoltage charging.

License

Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.