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275 lines
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275 lines
12 KiB
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<meta name="author" content="M.T. Konstapel" />
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<meta name="dcterms.date" content="2024-02-14" />
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<title>APRS digipeater</title>
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<header id="title-block-header">
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<nav id="TOC">
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<ul>
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<li>
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<a href="#">Index</a>
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<ul>
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<li><a href="#the-story" id="toc-the-story">The
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story</a></li>
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<li><a href="#the-design" id="toc-the-design">The
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design</a></li>
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<li><a href="#the-build" id="toc-the-build">The
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build</a></li>
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<li><a href="#the-specifications"
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id="toc-the-specifications">The specifications</a></li>
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<li><a href="#license" id="toc-license">License</a></li>
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</ul>
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</li>
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<li>
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<a href="https://git.meezenest.nl/marcel/aprs_digipeater_weather_telemetry">Git repo</a>
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</li>
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<li>
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<a href="https://meezenest.nl/mees/aprs_digipeater.html">Back</a>
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</li>
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</ul>
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<a href="https://www.meezenest.nl/mees/"><img alt="Logo" src="./images/mees_logo.svg" height="70"></a>
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</nav>
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<h1 class="title">APRS digipeater</h1>
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<p class="subtitle">with weather and PE1RXF telemetry server</p>
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<p class="author">M.T. Konstapel</p>
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<p class="date">2024-02-14</p>
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</header>
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<main>
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<article>
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<p><b>Abstract </b><p>This project is a collection of former (and some
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new) projects connected together to make an APRS digipeater, which
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doubles as an APRS weather station, with PE1RXF telemetry server
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capabilities.</p></p>
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<figure>
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<img src="./images/block_diagram_overview.svg"
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title="Block diagram ofdigipeater" alt="Block diagram of digipeater" />
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<figcaption aria-hidden="true">Block diagram of digipeater</figcaption>
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</figure>
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<h1 id="the-story">The story</h1>
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<p>For several years I operate an APRS iGate on both 2 meter and 70 cm
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LoRa. I added my own PE1RXF telemetry support (see: <a
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href="https://www.meezenest.nl/mees-elektronica/aprs_telemetry.html">https://www.meezenest.nl/mees-elektronica/aprs_telemetry.html</a>).
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This worked fine, but I already had designed an updated version of the
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iGate. The prototype worked, but had some issues. So I kept using the
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old iGate and forgot all about the new version.</p>
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<p>Some time ago I started to design a weather station (<a
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href="https://www.meezenest.nl/mees-elektronica/weather_station.html">https://www.meezenest.nl/mees-elektronica/weather_station.html</a>)
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which I located in the back garden. Because it was out of reach of my
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wifi network, I used the APRS iGate prototype to send the weather data
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via its build in LoRa modem to my PE1RXF telemetry server.</p>
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<p>Than the idea of relocating my existing iGate to the location of my
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weather station emerged. The weather station had all the hardware I
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needed build in. And it made sense to combine the two systems, as both
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handle APRS traffic. Besides, both systems use energy so shutting one
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down seems sensible.</p>
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<p>But the reason I used the APRS iGate prototype in the first place,
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namely the absence of wifi, became a problem again. An APRS iGate has to
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have access to the internet, that’s the whole point! But the amount of
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data it sends is small, so I didn’t need lots of bandwidth. And at that
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point another dormant project woke up: I always wanted to experiment
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with TCP/IP over the air. In the past I did some experiments with TCP/IP
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over AX.25 (packet radio), but the 1200 baud modems were simply too
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slow. I also had build a 5GHz HamNet link, but 350 Mbit/s is quite the
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overkill. I needed a link speed between 15kB/s to 500kB/s. The Rnode
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project from <a
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href="https://unsigned.io/hardware/RNode.html">https://unsigned.io/hardware/RNode.html</a>
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seemed perfect.</p>
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<h1 id="the-design">The design</h1>
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<h2 id="weather-station">Weather station</h2>
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<p>This project started with a weather station. I designed it as a stand
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alone weather station with an RS-484 ModBus interface. It can measure
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wind speed, wind direction, rain fall, humidity, air pressure and
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temperature. The complete build document of the weather station can be
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found here: <a
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href="https://www.meezenest.nl/mees-elektronica/projects/weather_station/build_doc/weather_station.html">https://www.meezenest.nl/mees-elektronica/projects/weather_station/build_doc/weather_station.html</a></p>
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<figure>
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<img src="./images/weather_station_sensors_small.jpg"
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title="Weather station" alt="Weather station" />
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<figcaption aria-hidden="true">Weather station</figcaption>
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</figure>
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<h2 id="brains">Brains</h2>
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<p>Although stand alone in operation, to read the measurements the
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weather station must be connected to a host via RS-485. This host is a
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Raspberry Pi LoRa shield I designed to be the successor of my first APRS
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iGate. It is a simple PCB with room for a Raspberry Pi Zero 2 W, a LoRa
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transceiver, a real time clock and a power supply.</p>
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<figure>
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<img src="./images/RPi-LoRa-shield_prototype.jpg"
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title="Raspberry Pi LoRa shield prototype"
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alt="Raspberry Pi LoRa shield prototype" />
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<figcaption aria-hidden="true">Raspberry Pi LoRa shield
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prototype</figcaption>
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</figure>
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<figure>
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<img src="./images/RPi-LoRa-shield_schematic.png"
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title="Raspberry Pi LoRa shield schematic"
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alt="Raspberry Pi LoRa shield schematic" />
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<figcaption aria-hidden="true">Raspberry Pi LoRa shield
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schematic</figcaption>
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</figure>
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<p><a href="./images/RPi-LoRa-shield_schematic.pdf">PDF version of
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schematic</a></p>
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<h2 id="peripherals">Peripherals</h2>
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<p>The Raspberry Pi needs some extra hardware for interfacing the
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various peripherals, like the transceiver, the ModBus and the Rnode
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modem.</p>
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<h3 id="usb-hub">USB hub</h3>
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<p>As the Raspberry Pi only has one USB port, a hub is essential. I used
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an old one I had laying around. Taken out of its case, it fits
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perfectly.</p>
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<h3 id="rs-485-dongle">RS-485 dongle</h3>
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<p>To interface with the weather station a USB to RS-485 dongle is
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needed. A cheap one from Joy-IT (<a
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href="https://joy-it.net/en/products/SBC-TTL-RS485">https://joy-it.net/en/products/SBC-TTL-RS485</a>)
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is fine.</p>
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<figure>
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<img src="./images/rs-485_dongle.webp" title="RS-485 dongle"
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alt="RS-485 dongle" />
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<figcaption aria-hidden="true">RS-485 dongle</figcaption>
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</figure>
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<h3 id="baud-aprs-modem">1200 baud APRS modem</h3>
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<p>This modem I also had laying around. It is called “Packet modem nano
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2” and it is based on the Micromodem from unsigned.io (<a
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href="https://unsigned.io/hardware/MicroModem.html">https://unsigned.io/hardware/MicroModem.html</a>).
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The design files for this modem are part of this project and can be
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found in the git repository.</p>
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<figure>
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<img src="./images/packetmodem_nano2_pcb_small.jpg"
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title="Packet modem nano 2" alt="Packet modem nano 2" />
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<figcaption aria-hidden="true">Packet modem nano 2</figcaption>
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</figure>
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<figure>
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<img src="./images/packetmodem_nano2_rev2.png"
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title="Packet modem nano 2 schematic"
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alt="Packet modem nano 2 schamatic" />
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<figcaption aria-hidden="true">Packet modem nano 2
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schamatic</figcaption>
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</figure>
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<p><a href="./images/packetmodem_nano2_rev2.pdf">PDF version of
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schematic</a></p>
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<h3 id="rnode-modem">Rnode modem</h3>
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<p>For the low speed network link I use the Rnode project from <a
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href="https://unsigned.io/hardware/RNode.html">https://unsigned.io/hardware/RNode.html</a>.
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This is an amazing project and I only use a small part of the features
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available. In my ow project is works as a KISS compatible LoRa modem.
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Together with the tncattach program (<a
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href="https://unsigned.io/software/tncattach.html">https://unsigned.io/software/tncattach.html</a>)
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it forms a Linux network adapter over which I can route all the network
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traffic. The maximum speed is just above 20 KB/s, which is enough for
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APRS-IS traffic. For archival reasons, I included the source code of
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tncattach as well as rns (the firmware and configuration utility) in the
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git repository.</p>
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<p>The hardware on which the Rnode firmware is flashed is a LilyGO
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LoRa32 v2.1 (also known as TTGO T3 v1.6.1). Of course you need at least
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two boards to form a network. With a good antenna, the range is easily
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100 meters (and probably more than 1 km), which is plenty enough for
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what I need.</p>
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<p>As a ham, I use the 433 MHz version, of course.</p>
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<figure>
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<img src="./images/lilygo-ttgo-lora32.jpg" title="LilyGO LoRa32"
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alt="LilyGO LoRa32" />
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<figcaption aria-hidden="true">LilyGO LoRa32</figcaption>
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</figure>
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<h2 id="more-than-brains-alone">More than brains alone</h2>
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<p>The Raspberry Pi with all the extra hardware is housed in a small
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plastic housing. On the back panel behind the SMA connectors and the
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power jack, I placed a copper strip. This acts as the star grounding
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strip on which all other ground wires are connected. This prevents a lot
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of RF and EMC problems.</p>
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<figure>
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<img src="./images/raspberry_pi_proto_small.jpg"
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title="Inside the brains" alt="Inside the brains" />
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<figcaption aria-hidden="true">Inside the brains</figcaption>
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</figure>
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<p><a href="./images/raspberry_pi_proto.jpg">Large version of
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photo</a></p>
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<figure>
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<img src="./images/raspberry_pi_proto_backside.jpg" title="Back side"
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alt="Back side" />
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<figcaption aria-hidden="true">Back side</figcaption>
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</figure>
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<h2 id="external-hardware">External hardware</h2>
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<h3 id="meter-transceiver">2 meter transceiver</h3>
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<p>The 2 meter transceiver is an old Alinco DJ-580 hand held radio with
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an output power of 5 Watt. It is connected to both the 5 pin DIN
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connector and the 12 Volt barrel jack on the Raspberry Pi.</p>
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<figure>
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<img src="./images/alinco_dj580t.jpg" title="Alinco DJ-580"
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alt="Alinco DJ-580" />
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<figcaption aria-hidden="true">Alinco DJ-580</figcaption>
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</figure>
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<h3 id="diplexer">Diplexer</h3>
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<p>The LoRa APRS transceiver (70cm) and the APRS transceiver (2m) are
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connected to a triplexer, making it possible to use one dual band
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antenna for both radios. Why a triplexer? Well, I had one laying around.
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I terminated the unused 1200MHz connector with a 50 Ohm load. But a
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diplexer would have been sufficient, of course.</p>
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<figure>
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<img src="./images/triplexer.png" title="Triplexer" alt="Triplexer" />
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<figcaption aria-hidden="true">Triplexer</figcaption>
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</figure>
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<h3 id="antenna">Antenna</h3>
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<p>This is a simple 2m/70cm dual band antenna from Diamond, the X30.</p>
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<figure>
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<img src="./images/diamond-x30.jpg" title="Antenna" alt="Antenna" />
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<figcaption aria-hidden="true">Antenna</figcaption>
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</figure>
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<h1 id="the-build">The build</h1>
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<h2 id="software">Software</h2>
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<p>The instalation of all the needed software on the Raspberry Pi is
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complicated, so I wrote a separate document: <a
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href="./installation_pe1rxf_aprs_weather_server.html">installation_pe1rxf_aprs_weather_server.html</a></p>
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<h1 id="the-specifications">The specifications</h1>
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<ul>
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<li>2 meter transceiver with 5 Watt output power</li>
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<li>70 cm LoRa transceiver with 20 dBm output power</li>
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<li>Raspberry Pi Zero 2 W</li>
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<li>APRS cross band digipeater software</li>
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<li>Weather station via ModBus</li>
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<li>Rnode TCP/IP over 70 cm LoRa for internet</li>
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</ul>
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<h1 id="license">License</h1>
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<p>Copyright (C) 2024 M.T. Konstapel</p>
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<p><a
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href="https://meezenest.nl/mees/">https://meezenest.nl/mees/</a></p>
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<p>The software is published as open-source software (GPL). The hardware
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is published as open-source hardware (OSH).</p>
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<h2 id="software-1">Software</h2>
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<p>This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by the
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Free Software Foundation, either version 3 of the License, or (at your
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option) any later version.</p>
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<h2 id="hardware-and-documentation">Hardware and documentation</h2>
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<p>This work is licensed under a Creative Commons Attribution-ShareAlike
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4.0 International License.</p>
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<hr>
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</article>
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<footer>
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<p>©
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2024-02-14
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M.T. Konstapel
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<a href="https://meezenest.nl/mees/">https://meezenest.nl/mees/</a>
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</p><p>This work is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by-sa/4.0/">Creative Commons Attribution-ShareAlike 4.0 International License</a>.
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</p>
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