Due to other, exciting distractions (which I will mention in a later post), I haven’t had a chance to keep the blog up to date. Still, work progresses on the boat, and that’s the important part. Last month, with the keel now in its new position about 30mm further back along the hull, and sealed into place, it was time to add the electronics board.
Posts From Category: Communications
A quick look at the almost-complete Sailboat Guidance System (SGS). The board on the left is Igor. Otto is on the right, and the main CPU (Mother) is hidden underneath. The ribbon cable brings all the I/O to and from the boards. The red insulating tape is to remind me of some of the last remaining wires which need to be connected. You can also just about make out the DC/DC converter which is just underneath the ribbon cable at the bottom of the picture.
As of about an hour ago, Igor and Mother exchanged communication. It was awkward, stilted communication, like a first date, but they talked! One of the issues with the RS232 stream is that the kernel is chatty. I’ve suppressed a lot of the boot-up messages, but there are still all those /etc/rc startup messages. As the ALIX board only has one serial port, those messages are sent to Igor. To avoid sending Igor into a tail-spin, or more importantly, sending the boat into a tail-spin, Igor ignores all RS232 output when Mother boots, until the magic word is sent over the wire. The magic word is XYZZY. Anyone want to try and figure out where that comes from?
Looking at the system power design, the majority of the circuits will run off a +5 volt rail. Those elements which need a different voltage, such as the main processor board, will derive their own requirements from the main Vcc rail.
There will be at least two Vcc busses on board. Labeled, oddly enough, as Vcc1 and Vcc2. The difference between them is that Vcc1 is always on, at all times, and Vcc2 (through VccN) are selectable by Igor.
The main processor runs off Vcc2, but Igor (and Otto) both run off Vcc1. In situations where voltage levels are critical, Vcc2 will be switched off and the boat will continue on whatever course had previously been set, until either voltage levels are healthy, the specified “wake-up” time has elapsed, or there are critical issues which require Mother to get involved. A critical situation could be something like a dramatic wind shift, or an error such as a mis-reading from a sensor.
There is a race requirement which states that “Any boat which fails to transmit for more than 10 consecutive days will be disqualified.”
While there are a number of ways of reporting position data back to Mission Control, from elaborate HF transmitters through to simple satellite position locators, we’ll be using a Rock Block satellite modem. These devices can send byte sequences back to dry land via the Irridium satellite network. We will be sending four updates a day, of exactly 250 bytes each. Each message will include two or more payloads.