9.3 photo

README.md

@@ -8,20 +8,23 @@ In 2018 I installed this system on my boat. It is still working fine after 2 yea
 
 ![Image](images/UnitExterior.jpg?raw=True "Exterior View")
 
-I have refined the design quite a bit, and it now has an official name. "Maiana" is an atoll in the Kiribati islands. I do intend to trademark this, in the same way that "Arduino" is a trademark that identifies the original rather than the many clones that inevitably emerged.
+I have refined the design quite a bit, and it now has an official name, "Maiana", borrowed from an atoll in the Kiribati islands. I do intend to trademark this, in the same way that "Arduino" is a trademark that identifies the original rather than the many clones which inevitably emerged.
 
 ## Overall description
 
 ### Hardware
 
 The main difference between this design and nearly every commercial transponder is that it's a standalone unit. It contains all of its
 radios and antennas and thus only needs a power and data cable to connect to the cabin. The PCBA is only 1" wide so it fits inside
-1" schedule 40 PVC pipe, which I used as the antenna base. The GNSS receiver and antenna are on the board:
+1" schedule 40 PVC pipe, which I used as the antenna base. The GPS receiver and antenna are on the board:
 
-![Image](images/transponder-6.1.jpg?raw=True "PCBA version 6.1")
+![Image](images/transponder-9.3.jpg?raw=True "PCBA version 9.3")
 
-The design is based on two Silicon Labs 4463 transceiver ICs and an STM32L4xx series microcontroller (L412 and L432 as of now).
-The GNSS is a Telit SE873 (7x7mm module) and relies on a Johanson ceramic SMD antenna. It usually takes about a minute to acquire a fix outdoors.
+The design is based on two Silicon Labs 4463 transceiver ICs and an STM32L412 series microcontroller. The 80MHz clock speed
+of the MCU allows the SPI bus to operate at exactly 10MHz which is the maximum supported by the Silabs RF ICs. This is crucial, as a transponder is
+a hard real-time application that relies on interrupts for precise timing of the transmit function, so SPI latency must be minimized.
+
+The GPS is a Quectel L70R module and relies on a Johanson ceramic SMD antenna. It usually takes a little over a minute to acquire a fix outdoors.
 The transmitter output is 2 Watts (+33dBm) and it has a verified range of over 10 nautical miles.
 
 The unit runs on 12V and exposes a 3.3V UART for connecting to the rest of the boat's system. The UART continuously sends GPS and AIS data in NMEA0183 format at 38.4Kbps.
@@ -33,9 +36,9 @@ The unit implements SOTDMA synchronization based on the very acurate 1 PPS signa
 It will just transmit autonomously and independently, based on Clear Channel Assessment, at the schedule permitted for class B devices. If station data is not provisioned, the device
 will simply run as a receiver and never transmit.
 
-The system draws about 40mA from 12V in RX mode, and spikes up to 600mA during transmission (for about 30 milliseconds).
+The system draws about 30mA from 12V in RX mode, and spikes up to 600mA during transmission (for about 30 milliseconds).
 
-The latest design (6.1 pictured above) relies on plain Ethernet cable for power, data, and control signals such as "TX OFF". I will include a reference design for a
+The latest design (9.3 pictured above) relies on plain Ethernet cable for power, data, and control signals such as "TX OFF". I will include a reference design for a
 control box that I'm working on but every boat is different, so your mileage will absolutely vary.
 
 
@@ -48,8 +51,8 @@ the required symbols in the preprocessor to build for different board revisions.
 
 This is going to be difficult for all but the most technically advanced.
 
-The board features all surface mounted components, with 5 QFNs, a few SOT-363s and all 0603 passives. Unless you're skilled with stencils and reflow, you will find it challenging. So I am going to make it available as part of a kit on tindie.com. The kit will include a 95% finished PCBA as well as the VHF antenna, 
-enclosure and sealing components (which are NOT open sourced). The board will be programmed and tested, and the antenna will be perfectly matched. The cable and whatever lies on the other side of it will be the buyer's responsibility. 
+The board features all surface mounted components, with 4 QFNs, a few SOT-363s and tightly spaced 0603 passives. Unless you're skilled with stencils and reflow, you will find it challenging. So I am going to make it available as part of a kit on tindie.com. The kit will include a 95% finished PCBA as well as the VHF antenna, 
+enclosure and sealing components (which are NOT open sourced). The board will be programmed, tested and calibrated, and the antenna will be perfectly matched. The cable and whatever lies on the other side of it will be the buyer's responsibility. 
 
 ### License
 
@@ -59,10 +62,6 @@ So don't try anything fishy, because I *will* find out and then ... well, let's
 If you're a tinkerer and want to further this design while adhering to the GPL, more power to you! Build it, sell it, give it away, do whatever you want to get it out there. 
 You cannot, however, use the MAIANA™ name in a forked design, as it will be trademarked. Just call it something else.
 
-### Concluding thoughts
-
-The commercial AIS industry has not exactly been successful in the low-cost recreational boating market, and with prices like $500-$800 for a unit that has a bunch of external 
-dependencies that's hardly a surprise. I hope to change that.