Hack, Make, Teach
Lately I’ve been working on the knitting machine code some more. First, the thing that will affect fellow hackers and knitters the most -
Update 3/1/12: After some more thought, I’m recommending against simply using a serial adapter, as I had previously written here. My reasoning is this -
While I’d like to make it as easy as possible for people to connect to their knitting machines, I’ve only tested this on one model of machine. A standard USB serial module may present voltages to the knitting machine which are outside the range that the external drives do. While I’ve determined that this is probably safe for the one model of knitting machine that I have, I can’t be sure that it’s not going to stress the input circuitry on some models. The absolute safest way to do this is to use the exact same signal voltages that the external disk drive does. In order to do this, using an FTDI interface is the best way. The cost for using adafruit’s “FTDI Friend” is only about $5 more than using a standard serial interface, and since these old knitting machines are irreplaceable and often very expensive when you can find them, I’d rather do this the absolute safest way. I have no reports of problems from using regular serial interfaces, but I think that this is a case where absolutely correct engineering is more appropriate than a hack to save a few dollars.
I’ll be updating the wiki page very soon with directions for how to use the FTDI Friend to interface with the knitting machine.
I’ve now thoroughly tested connecting a PC to the knitting machine using only a standard USB serial adapter. This means that you don’t have to fool with FTDI interfaces, inverting signals, etc. All it takes is a serial adapter, a female DB-9 connector, and four jumper wires. That’s documented on the wiki page.
This makes it much easier for the less technical among us to connect their machine to a computer.
The rest will have more impact in the long run . . .
I’ve obtained an actual Brother FB100 external floppy drive, and successfully connected it through a serial adapter. It requires a 5V adapter – I’m using the adafruit FTDI friend. It’s a little complex – you have to rejumper and reprogram the FTDI friend. That’s also documented on the wiki page here.
There are some files currently in the ‘experimental’ directory in the source repo which communicate with the disk drive, and extract information from knitting machine disks into the format used by my disk emulator. I’m planning to use these to help fill in some gaps in knowledge about the file format used by the knitting machine.
Most people won’t have use for this code to interface with the floppy drive, as the drives are rare.
I have other plans for this investigation, so I may have more to say about it soon.
I had published my floppy drive emulator for the brother knitting machine, and some other information, using the wiki here at antitronics. This was sub-optimal from the beginning, and since Lady Ada published some of that in her git repo here: https://github.com/adafruit/knitting_machine, I’ve been intending to get more of my files out there. Limor’s repo seemed like the best place to put them, and she’s graciously allowed me to add them. What documentation I’ve created about the brother data format is in there, as well as all the hacked-up tools I used to help with the reverse engineering. There’s nothing there for anyone wanting easily usable end-user applications, sorry about that.
As usual, I’d love to hear from anyone who finds these to be useful.
Bdale Garbee and Keith Packard are both longtime Debian Developers, and have a pile of code to their credit. They’ve presented at a number of conferences and almost always find a way to work their passion for rocketry into their presentations. They are both amateur radio operators.
At the Linux Collaborative Summit last week, I had a chance to talk with them, and the topic drifted quickly to Rocketry and Amateur Radio, and the intersection of those interests. They’ve created the TeleMetrum telemetry system, available soon from their Altus Metrum site. This is an amazing platform that has applications beyond rocketry – a GPS, accelerometer, and altimeter with a telemetry link in the 70cm amateur band. it’s all open hardware and open software.
They’re about to open shop and start selling these, and I know it’s going to be a big deal for a lot of people in Rocketry. I can also see uses for high altitude balloon launches.
I’m not into rocketry any more, and there’s no room in my hobby load for that, but I was really interested in the programmable radio chip that they are using. The same chip is used on both the rocket and for the ground station, and the ground station unit is available as the TeleDongle. The TeleDongle is a complete radio system with 10mW output on the 70 cm band, powered from a USB port. As supplied, it has code installed from Keith which makes it a virtual 38k4 serial link. With different output filter values, the chip can function over a wide range of frequencies, but it’s only certified in certain bands. I’m still digesting the data sheet, but there’s an amazing amount of functionality on the chip.
Happily, I was able to order a couple of the TeleDongles from Bdale, and I got notice today that he has shipped them. They’re set up so that you can use one as a USB adapter to program the other, making experimentation easier. I’m looking forward to experimenting with these. I’ll post the results!