Traditionally, modules such as GPS and AIS communicate with a serial protocol such as RS232 or RS422, whether or not packaged in a virtual COM port over USB or Bluetooth. That principle, of one producer supplying "hard-wired" data to one consumer, has its limitations. This becomes immediately clear when several customers have to be served or sensors of completely different nature have to work together. And, finally, it lacks a constact factor around which things can be organized in time. A marketplace where supply and demand of data come together, enrich each other, and remain available. An MQTT broker acts as a spider in the web and takes care of this. How to get from AIS via NMEA -> JSON -> Wi FI -> MQTT -> Node-Red -> both in every corner of the hobby space and in the wide world? That's what this story is about.
The AIS receiver described in this article is an update to an earlier version that revealed some issues in the print layout. Since I had to place an order for some other PCB projects anyway, I let this corrected version run along and also took the opportunity to add an extra Si4362 (or Si4463) to the design for dual channel simultaneous AIS-receipt.
About seven years ago I designed an information system for law enforcement along Europe's waterways and seaports: AQUATRACK. I then equipped the remote receiving stations with a AIS receiver OEM module from SRT Marine Systems. An excellent product. The phenomenon of AIS fascinated me so much that I was curious if I could make a building block as a hobby project for a fraction of the cost. A search on the internet led me to a nice initiative, the dAISy project which turned out to be based on an EZRadioPRO ISM Band receiver chip: the Si4362 from Silicon Labs and a simple 8-bit MSP430 processor from Texas Instruments. Because I am a little more comfortable on ARM processors and also have the development tools for it, I'd rewrote the source code for a Cortex M0 chip, the STM32F042K6 from STMicroelectronics to be precise. I also made some print circuit board designs for this.
It must have been in the early '70s that I became interested in data transmission over radio. My school for Electrial Engineering in Amsterdam (the ETS, a great school) supported my enthusiastic and gave me two Siemens T37 telex machines. Those things weighed a ton, and it was a hell of a job to get them going again, but after a lot of fiddling with audio filters and discriminators, I finally knew the converting alternating tones on the shortwaveinto legible writing. And vice versa! "RYRYRYRYRYRYRY CQ CQ CQ de PE1BOS" A little later I got access to a beautiful sky-blue Siemens T100S Telex, complete with punched tape writer/reader. After that it became a green teletype video display unit and a IBM EBCDIC keyboard that I converted to ASCII and - later still - the Apple II+ with its plug-in cards and various TNCs for AMTOR, FEQ and AX25.
With the EZRadioPro series, Silicon Labs offers a range of attractive receiver and transceiver chips in a QFN20 package for telemetry applications in the sub-GHz range. There are also complete modules equipped with this IC for little money (including on AliExpress). For home automation applications on 433 or 866 MHz I usually use the comparable RFM69 from HopeRF, but what makes the Si4463 special is the enormous continuous frequency range (142 - 1050 MHz), the fact that the VHF band is part of this and especially the maritime AIS-channels (161.975 and 162.025 MHz) come into view.
Building on the work of PA0NHC en LZ1AQ (and as a kick-off in this blog) a design for a broadband magnetic loop antenna amplifier. It consists of two printed circuit boards. The first for the actual amplifier, and a second, as an RF/DC splitter placed near the receiver. I moved a year ago, which roughly coincided with my retirement. Two reasons to pick up my old hobby of amateur radio again after years. It would have been no different at my old house, but what immediately struck me once I had installed a dipole antenna was the extremely high interference level. Apparently a sum of all solar panels, power line adapters and LED lighting drivers that are commonplace today. All in all it produces a quite interesting radio spectrum but pretty unusable for HAM radio. All this misery didn't seem like the most appropriate reason to honor all my new neighbors with a first visit. Before saying goodbye to a once beautiful hobby, the aim was a last attempt to find some useful (FT8) signals in this huge mountain of QRM / EMC / EMI / RFI.