Ignition!
Whilst the chemistry was sometimes over my head, this book is an engaging summary of the history of US liquid rocket fuels during the height of the cold war. Fun to read and interesting as well. I enjoyed it.
Using a MCP4921 or MCP4922 as a SPI DAC for Audio on Raspberry Pi
I've been playing recently with using a MCP4921 as an audio DAC on a Raspberry Pi Zero W, although a MCP4922 would be equivalent (the '22 is a two channel DAC, the '21 is a single channel DAC). This post is my notes on where I got to before I decided that thing wasn't going to work out for me. My basic requirement was to be able to play sounds on a raspberry pi which already has two SPI buses in use. Thus, adding a SPI DAC seemed like a logical choice. The basic circuit looked like this: Driving this circuit looked like this (noting that this code was a prototype and isn't the best ever). The bit that took a while there was realising that the CS line needs to be toggled between 16 bit writes. Once that had been done (which meant moving to a different spidev call), things were on the up and up. This was the point I realised that I was at a dead end. I can't find a way to send the data to the DAC in a way which respects the timing of the audio file. Before I had to do small writes…
1-Wire home automation tutorial from linux.conf.au 2019, part 2
For the actual on-the-day work, delegates were handed a link to these instructions in github. If you're playing along at home, you should probably read 1-Wire home automation tutorial from linux.conf.au 2019, part 1 before attempting the work described here. Its especially important that you know the IP address of your board for example. Relay tweaks The instructions are pretty self explanatory, although I did get confused about where to connect the relay as I couldn't find PC8 in my 40 pin header diagrams. That's because the shields for the tutorial have a separate header which is a bit more convenient: I was also a bit confused when the relay didn't work initially, but that turns out because I'd misunderstood the wiring. The relay needs to be powered from the 3.3v pin on the 40 pin header, as there is a PCB error which puts 5v on the pins labelled as 3.3v on the GPIO header. I ended up with jumper wires which looked like this: 1-Wire issues Following on the tutorial instructions worked well from then on until I tried to get 1-Wire setup. The owfs2mqtt bridge plugin was logging this: 2019-04-08 19:23:55.075: /opt/OWFS-MQTT-Bridge/lib/Daemon/OneWire.pm:148:Daemon::logError(): Connection to owserver failed: Can't connect…
1-Wire home automation tutorial from linux.conf.au 2019, part 1
I didn't get much of a chance to work through the home automation tutorial at linux.conf.au 2019 because I ended up helping others in the room get their Orange Pi is booting. Now that things have settled down after the conference, I've had a chance to actually do some of the tutorial myself. These are my notes so I can remember what I did later... Pre-tutorial setup You need to do the pre-tutorial setup first. I use Ubuntu, which means its important that I use 18.10 or greater so that st-link is packaged. Apart from that the instructions as written just worked. You also need to download the image for the SD card, which was provided on the day at the conference. The URL for that is from github. Download that image, decompress it, and then flash it to an SD card using something like Balena Etcher. The tutorial used 32gb SD cards, but the image will fit on something smaller than that. hassos also doesn't put anything on the Orange Pi HDMI port when it boots, so your machine is going to look like it didn't boot. That's expected. For the tutorial we provided a mapping from board number (mac…
Introducing GangScan
As some of you might know, I am a Scout Leader. One of the things I do for Scouts is I assist in a minor role with the running of Canberra Gang Show, a theatre production for young people. One of the things Gang Show cares about is that they need to be able to do rapid roll calls and reporting on who is present at any given time -- this is used for working out who is absent before a performance (and therefore needs an understudy), as well as ensuring we know where everyone is in an environment that sometimes has its fire suppression systems isolated. Before I came along, Canberra Gang Show was doing this with a Windows based attendance tracking application, and 125kHz RFID tags. This system worked just fine, except that the software was clunky and there was only one badge reader -- we struggled explaining to youth that they need to press the "out" button when logging out, and we wanted to be able to have attendance trackers at other locations in the theatre instead of forcing everyone to flow through a single door. So, I got thinking. How hard can it be to build…
Brilliant Smart Wifi plug with Tasmota
A couple of weeks ago I was playing with Tuya derived smart light globes (Mirabella Genio from K-Mart Australia in my case, but there are a variety of other options as well). Now Bunnings has the Brillant Smart Wifi Plug on special for $20 and I decided to give that a go as well, given it is also Tuya derived. The basic procedure for OTA flashing was the same as flashing the globes, except that you hold down the button on the device for five seconds to put it into flash mode. That all worked brilliantly, until I appear to have fat fingered my wifi details in Tasmota -- when I rebooted the device it never appeared on my network. That would be much more annoying on the globes, but it turns out these smart plugs are really easy to open and that Tuya has documented the pin out of the controlling microprocessor. So, I ended up temporarily soldering some cables to the microprocessor to debug what had gone wrong. It should be noted that as a soldering person I make a great software engineer: Once you've connected with a serial console, its pretty obvious who can't be trusted to…
I, Robot
Not the book of the movie, but the collection of short stories by Isaac Asimov. I've read this book several times before and enjoyed it, although this time I found it to be more dated than I remembered, both in its characterisations of technology as well as it's handling of gender. Still enjoyable, but not the best book I've read recently.
Mirabella Genio smart lights with Tasmota and Home Assistant
One of the things I like about Home Assistant is that it allows you to take hardware from a bunch of various vendors and stitch it together into a single consistent interface. So for example I now have five home automation vendor apps on my phone, but don't use any of them because Home Assistant manages everything. A concrete example -- we have Philips Hue lights, but they're not perfect. They're expensive, require a hub, and need to talk to a Philips data centre to function (i.e. the internet needs to work at my house, which isn't always true thanks to the failings of the Liberal Party). I'd been meaning to look at the cheapo smart lights from Kmart for a while, and finally got around to it this week. For $15 you can pickup a dimmable white globe, and for $29 you can have a RGB one. That's heaps cheaper than the Hue options. Even better, the globes are flashable to run the open source Tasmota stack, which means no web services required! So here are some instructions on flashing these globes to be useful: Buy the globes. I bought this warm while dimmable and this RBG option. Flash to…
What If?
More correctly titled "you die horribly and it probably involves plasma", this light hearted and fun read explores serious answers to silly scientific questions. The footnotes are definitely the best bit. A really enjoyable read.
Abaddon’s Gate
This is the third book in the Leviathan Wakes series by James SA Corey. Just as good as the first two, this is a story about how much a daughter loves her father, perhaps beyond reason, moral choices, and politics — just as much as it is the continuation of the story arc around the alien visitor. Another excellent book, with a bit more emphasis on space battles than previously and an overall enjoyable plot line. Worth a read, to be honest I think the series is getting better.