Sunday, May 28, 2017

How to load Taulabs onto an Openpilot Revolution mini

While Sparky2 is probably the best go-to board for Taulabs, the Revo mini can actually be bought, since it's usually in stock...
So instead of waiting who knows how long for someone to have a Sparky2 in stock, I bought a Revo mini. If you compare the 2, you'll see that there's only minor (but still important) differences.
Revo mini schematic vs Sparky2 schematic
There's just the issue of Taulabs not detecting the board with the Openpilot bootloader. You can try and go the masochistic route, or you can actually do it the easy way.

  1. download and install both Taulabs and Librepilot groundstations.
  2. download the Linux version of Taulabs (regardless of your OS) and extract, (7zip works well) somewhere in there you'll find the bootloader *.bin file
  3. use Librepilot to:
    1. HALT the MCU and go into bootloader mode (firmware tab)
    2. !!!back up the original firmware!!!!
    3. select the proper *.bin file (only the bootloader!), tick the warning boxes and upload the bootloader. If you fuck up somehow, it should still be possible to rescue the board with the previously saved firmware.
  4. close Librepilot, open Taulabs, go to firmware tab, it should now recognize the board in bootloader mode
  5. load latest firmware release, boot the board, check if it works.

Sunday, April 2, 2017

Console over RS232 on a Nortel 4550t switch

  1. straight, female-female cable (seriously check that it's straight, pins 2 and 3 must not be crossed)
  2. serial port (TTL-level devices don't seem to work - at least it didn't for me - so make sure it's a real RS232)
  3. some terminal program, putty works well enough
  4. select the right COM port, 9800 baud, 8N1...the bog-standard for slow serial

If you see text while the switch is booting, you're golden. If not, something is not working the way it's supposed to.
Before you can start wreaking havoc in the console, you have to wait for the switch to boot. There is a procedure to get console before boot, but that is generally useful only if you locked yourself out.
Once you get the ASCII-art logo, press CTRL+y, then type "en" or "enable". Let the typing begin.

Sunday, November 13, 2016

Using a Dell D220P-01

In case you don't know what a Dell D220P-01 is - it's a power supply for the SFF version of Dell's Optiplex 740 series PC. The neat thing about it is that unlike a traditional ATX PSU, this one is 12V only, so you get 220W @ 12V (18A) maximum and the PSU should not complain too much.
Another neat thing about them is that the PCs are legitimately junk, so you can get them even for free.
Stolen from
The pinout is in the picture, "P5" has to be connected to ground in order for it to turn on. Unlike newer server PSUs, this one can be connected straight from the start.
If you're like me and don't feel like butchering the connector, you'll need a breakout board. The connector is mechanically (!not electrically!) compatible with an 8-pin EPS12V power connector (plug is Molex 39-01-2080, PCB socket is  Molex 39-28-1083, terminals are Molex 39-00-0168 and Molex 44476-1111).
The 8-pin PCIe power connector is different with the placement of the square and hexagonal holes and is not mechanically compatible...not like that will stop the 200 pound gorilla from trying to jam it in...
Needles to say that if you plug this (and turn it on) into an EPS12V connector of a working motherboard, you will turn it into a non-working one, as the voltage is inconveniently reversed and the power supply will turn on. Results may vary from nothing at all to a spectacular fire and mini explosions of the caps.
stolen from
If your junkbox doesn't contain a motherboard with an 8-pin EPS connector, fret not, there is an alternative!
24-pin ATX...cut on the red lines...
stolen from wikipedia

Yep, it's not a true hack unless it involves a hacksaw!
side note - on any newer-ish junk motherboard, I suggest cutting the connector out, as the inner power layers use thicker copper (for heatsinking) and carry away heat from the soldering, making it very difficult.

As said earlier, plugging this PSU here to the MB is also not a good idea, although it should not turn on (results may vary). If the PSU does turn on, it will be short-circuited, if it "wins" over the short (burns through), it will send 12V to a 5V line...

Here's my quick and (really) gritty breakout board.

Yes, it's fugly, yes, it could've been nicer...I was going for "fugly, but functional". The crapton of solder should make sure that it can actually carry the 18A the PSU can deliver.
I kept the +12V rail from being at the edge, as it lowers the chance of an accidental short. The brass washers are actually soldered to the board.

Saturday, November 5, 2016

Smaller & lighter

While Totally not a bomb Mk II was useful for testing, it was a little too bulky even for the 1:10 car, so it was time to go shopping again...


  • 1x Raspberry Pi Zero 1.3
  • 1x 0.5mm pitch to 1mm pitch 15pin FPC cable
  • 1x TL-WN722N
  • 1x male RSMA connector with pigtail
  • some Kapton tape
  • enough 0.5mm sheet aluminium to make a box
  • ?x M2 screws
  • 1x XL6009 adjustable step up down Converter (DSN6000AUD)
The procedure:

1) Liberate the TL-WN722N out of it's plastic casing
2) perform UglyHack™ No.1 by desoldering the USB connector and solder on wires instead. Solder the other end fo the data lines into the USB port of the Rpi and solder the power to the power USB port of the Pi. PP1 is +5V, PP6 is gnd, PP22 is D+ and PP23 is D-. Twist the data lines to avoid weird shit from happening.
Grade-A hacking here!
the Kapton tape really is necessary...
Make liberal use of Kapton tape, covering all the exposed pads to avoid short circuits later.
3) Perform UglyHack™ No.2 by desoldering the RSMA connector and soldering on the pigtail one.
Again, Kapton tape is a must, not only as an electrical insulator, but also strain relief.

4) add the DC-DC power module (forgot pics, sry)
5) make an aluminium enclosure like so:
The other half is just a rectangular "U" shape, some of the holes are actually threaded.
6) Jam everything in, making sure that nothing is touching where it shouldn't.
In my implementation, the Pi is held a few mm away from the wall with screws and nuts on flexible washers. Some day I'll probably add a thermal pad between the main IC and the box, it does get warm.
The metal shield of the WiFi dongle is in direct contact with the wall to aid cooling, as it gets fairly hot when running with EZ-wifibroadcast. The DC-DC module is not even warm to the touch, so it can just float in the middle.
7) connect camera, strain-relive the cable so it doesn't get damaged.
Bottom scale is mm, top is inches.
Definitely could be made even smaller!

8) attach to desired mode of transport
Totally not a bomb Mk III
Camera holder needs to be adjustable...
Antennas for WiFi and RC
A few notes:
  • The antenna arrangement here is not ideal, the WiFi and RC systems interfere with each other, they should probably at least be further apart... (or I should use 5 GHz WiFi).
  • EZ-wifibroadcast on default runs outside of allowed WiFi bands (shhh, don't tell anybody...) and I keep it that way, there really isn't anything critical or even important using this band and it keeps the mutual interference with other WiFi to a minimum.
  • There are 5 GHz modules that are known to work with wifibroadcast if you want to avoid interference in the 2.4 GHz band.
  • The XL6009 module should safely operate between 4V to 30V. Pushing the voltage to the limits is asking for it.
  • The XL6009 is superior to LM2577 in that it runs at 400kHz instead of 50kHz, meaning the inductors can be much smaller.
  • If you feel lucky or actually know how to design a better DC-DC module, you can run both the dongle and Rpi directly on 3.3V. Be however aware, that if you fuck up, you'll fry them both.
  • If I ever make this smaller, I'll use one of the fancier DC-DC controllers that run at 1MHz, so the inductors are even smaller and the ripple is easier to filter out.
  • I advise using EZ-wifibroadcast as it boots much faster.
  • Last but not least, keep in mind that the sytem draws slightly over 2.5W and most of this is dumped as heat between the Rpi and the WiFi dongle, you have to allow air to flow around the box, otherwise it might overheat.

Saturday, April 16, 2016

Wifibroadcast - measuring latency on a laptop

My method of measuring the absolute latency scene-to-screen involves the camera looking at the receiver screen which is partially obstructed by a smartphone running a stopwatch, all being recorded by a Casio EX-F1 at 600fps.

The darker one is the smartphone screen, the lighter, grainy one is the laptop. I picked shots where both numbers are not blurred as they are changing.
Phone has an LCD, not AMMOLED display, so it tends to blur fast changing stuff. Both displays (phone and laptop) should be TFT, so about as fast as a consumer-grade LCD can be.

The mathematical average of these 10 shots is 197ms. Not too bad...

Sunday, April 10, 2016

Wifibroadcast receiving on a PC

Yup, you definitely can watch on a PC. (And there's no limit on how many! :D)
Tested on a Lenovo x230 running Ubuntu 14.01 LTS x64 with a TP-Link TP-WN722N.

Installing wifibroadcast:
open Terminal or some other commanline and input:

  • sudo apt-get install mercurial libpcap-dev iw
  • hg clone
  • cd wifibroadcast
  • make
If there's no screaming or error, you may proceed with connecting the wifi card and waiting until it lights up. Then proceed with setting it up:
  • cd $HOME/wifibroadcast
  • sudo ifconfig wlan1 down
  • sudo iw dev wlan1 set monitor otherbss fcsfail
  • sudo ifconfig wlan1 up
  • sudo iwconfig wlan1 channel 13
Run the program with:
  • sudo ./rx -b 8 -r 4 -f 1024 wlan1 | gst-launch-1.0 -v fdsrc ! h264parse ! avdec_h264 !  xvimagesink sync=false
Once there is a valid signal from the transmitter, the wifi LED will start flashing and shortly after you should see a window with the stream pop up. 
To infinity and beyond!

You can close it with ALT+F4 and stop the wifi with 

  • sudo ifconfig wlan1 down

To start it up again, repeat the setup (no need to install anything again) and run the program. Here I'm using wlan1, because I'm assuming that like me, you'll be using a laptop, so wlan0 will likely be taken by the internal wifi card. This may however not be the case, unless you are sure, check with ifconfig

Scripting it because typing everything is for noobs

1) create a new file (with no extension) and open with a text editor of your choice (I used gedit)
2) paste the following into it:
  • cd $HOME/wifibroadcast
  • ifconfig wlan1 down
  • iw dev wlan1 set monitor otherbss fcsfail
  • ifconfig wlan1 up
  • iwconfig wlan1 channel 13
  • ./rx -b 8 -r 4 -f 1024 wlan1 | gst-launch-1.0 -v fdsrc ! h264parse ! avdec_h264 !  xvimagesink sync=false
3) save to a convenient place, like /home
4) type the following into terminal, replacing "script_name" with the actual one you saved:
  • chmod 755 "script_name"
This gives the script read and write permissions.
5) to run the script, you only have to type:
  • sudo ./script_name
Again, replacing "script_name" with the actual one. You have to use sudo, because it needs permissions to tweak the wifi dongle. Without it, it'll never run.

Saturday, April 9, 2016

Dual boot for Windows 8 with Bitlocker and Ubuntu 14.01 LTS, UEFI version

  • Make sure you are booting in UEFI, not legacy mode. Seriously, check that shit.
  • Turn off secure boot.
  • Windows 8 goes first. For good measure, make sure the drive is GPT, not MBR. This can be done even in the install by clicking the "repair" and clicking your way to a commandline (tons of how-to's on teh interwebs)
  • If you need to make a UEFI-capable install USB flash, simply use diskpart to: 1) clean the drive 2) convert to GPT 3) create a primary partition DO NOT mark it active!!! 4) format it to FAT32 5) assign a letter. Close Diskpart, if you have a ISO somehow extract it (W8 and later can mount ISOs as a virtual drive; winzip can open it like an archive), dump the contents straight to the flash.
  • Create a patition for windows, make sure you leave enough space for Ubuntu, 10GB seems to be the recomended minimum. Windows installer should tell you that it's going to create additional pratitions, there should be a total of 4 including the one you made.
  • After the install and initial config, set up Bitlocker, save the keyfile outside the encryped drive, encrypt drive. Take ownership of the TPM. Reboot and make sure it works.
  • Disable fast boot, otherwise stuff WILL BREAK. There's little difference having it on for SSDs, magnetic drives are a different story though. The checkbox can be found in power management ->buttons setup ->the top "change what you can't now..." checkbox -> allow fast boot (uncheck).
  • Install Ubuntu. Bootable USB the same way as for windows. I chose 14.01 LTS, but I see no reason the newer versions would not work. Run the setup in "install alongside windows" mode. Partitions can be shrunk later. Make sure you note down all the passwords and pass phrases you set up. Test Ubuntu boot.
  • Test Windows boot. Most likely it will require you to input the key that you should have saved outside the encrypted drive. If you didn't, you're a dumbass and now have locked yourself out. Best start over.
  • boot Ubuntu, Change UEFI boot order via efibootmgr - in terminal type sudo efibootmgr -v  to see whats going on (you'll see quite a few  things with 4-digit numbers, and the boot order), then type sudo efibootmgr -o with the altered boot order. You'll most likely be switching the 2nd for the first. This is not fuck-up-resistant! You screw up - no worky worky!
  • If windows boot works, reboot again. If it keeps requesting you input the key every time you boot, you have to take ownership of the TPM again. If the greedy bastard keeps insisting you input the key over and over again despite you taking ownership of the TPM, something's fucked up and you have a long Google session ahead of you.
  • You will most likely not see any mention of Ubuntu during boot anymore, but fret not, try mashing whatever key brings up the boot menu before it starts booting, you should see "windows...something" and "ubuntu". This will be the way for choosing. Should also work for additional UEFI installs, the names seem to match the directories in the \EFI  
  • Turn secure boot back on
  • Install drivers and crucial software for both systems, make a disk image. Seriously, do that, the time you save when reinstalling is makes this worth it. Save the keys, passwords and passphrases with the image, as it's useless without them.
  • Enjoy your dual-boot.

This was done on a Lenovo x230 running an aftermarket SSD, Windows 8.1 and Ubuntu 14.01 LTS, all from UEFI-capable bootable USB flash drives. Both OSs run in secure mode with no bitching.
The boot menu is slow to load (10s for me), but that seems to be feature, not a bug.
Your results may vary, as i uderstand UEFI implementation is not perfectly the same for all PCs.