Useful information about NixOS

Since a few years i use NixOS as my favorite Linux distribution. NixOS is a Linux distribution based on the Nix package manager and build system. It supports reproducible and declarative system-wide configuration management as well as atomic upgrades and rollbacks, although it can additionally support imperative package and user management. See NixOS Wiki.

Upgrade to new version

  1. Review the NixOS release notes to ensure you account for any changes that need to be done manually. In particular, sometimes options change in backward-incompatible ways.

  2. sudo nix-channel --add https://nixos.org/channels/nixos-22.05 nixos (Change version tag if necessary)

  3. sudo nix-channel --update

  4. nixos-rebuild --upgrade boot

  5. Reboot to enter your newly-built NixOS.

It‘s perfectly fine and recommended to leave system.stateVersion value in the configuration at the release version of the first install of this system. You should only bump this option, if you are sure that you can or have migrated all state on your system which is affected by this option. Before changing this value read the documentation for this option (e.g. man configuration.nix or on NixOS Options).

Clean up system

  1. sudo nix-collect-garbage --delete-older-than 30d

Upgrade Kernel to latest version

  1. Add boot.kernelPackages = pkgs.linuxPackages_latest; to your configuration.nix

Use pipewire for Audio (with Bluetooth)

sound.enable = false;
hardware.pulseaudio = {
  enable = false;
  package = pkgs.pulseaudioFull;
};
security.rtkit.enable = true;
services.pipewire = {
  enable = true;
  alsa.enable = true;
  alsa.support32Bit = true;
  pulse.enable = true;
  # If you want to use JACK applications, uncomment this
  #jack.enable = true;

  # use the example session manager (no others are packaged yet so this is enabled by default,
  # no need to redefine it in your config for now)
  #media-session.enable = true;
  config.pipewire = {
    "context.properties" = {
      #"link.max-buffers" = 64;
      "link.max-buffers" = 16; # version < 3 clients can't handle more than this
      "log.level" = 2; # https://docs.pipewire.org/#Logging
      #"default.clock.rate" = 48000;
      #"default.clock.quantum" = 1024;
      #"default.clock.min-quantum" = 32;
      #"default.clock.max-quantum" = 8192;
  };
  media-session.config.bluez-monitor.rules = [
    {
      # Matches all cards
      matches = [ { "device.name" = "~bluez_card.*"; } ];
      actions = {
        "update-props" = {
          "bluez5.reconnect-profiles" = [ "hfp_hf" "hsp_hs" "a2dp_sink" ];
          # mSBC is not expected to work on all headset + adapter combinations.
          "bluez5.msbc-support" = true;
          # SBC-XQ is not expected to work on all headset + adapter combinations.
          "bluez5.sbc-xq-support" = true;
        };
      };
    }
    {
      matches = [
        # Matches all sources
        { "node.name" = "~bluez_input.*"; }
        # Matches all outputs
        { "node.name" = "~bluez_output.*"; }
      ];
      actions = {
        "node.pause-on-idle" = false;
      };
    }
  ];
};
};

Add a power LED to a Weller WE1010 soldering station

Some time ago I bought a Weller WE1010 soldering station. On all product photos it looks as if the display has a backlight – unfortunately this is not the case. Not even the on/off switch is illuminated, like on the old models. Shame on you Weller, that really goes better – especially for the price!

A backlight for the display would improve the readability enormously, but a retrofit is not so easy. I have instead installed a light under the on/off switch to see at least better whether the soldering station is switched on. I get the power directly from transformer, which supplies around 24V/AC. As LED i used this great Red 6mm 12-24V AC/DC LED.

Disclaimer

I assume no warranty or responsibility for any damage or injury. The conversion is at your own risk! When opening devices that are operated with mains voltage there is danger to life!

Parts

Assembly

  1. Open soldering station by removing the two screws on the back
  2. At this point, the housing can be carefully lifted with a flat screwdriver
  3. Then I removed the on/off switch and drilled a 6mm hole 12mm below the opening for the LED. Since there is so much space, one could think that Weller wanted to install an LED here – who knows?
  4. Insert the LED
  5. Protect LED cables with some tube
  6. Solder LED wires to the 24V output from the transformer
  7. Test and reassemble

Images

Video

Links

The links to AliExpress are advertising links. I would be happy if you use this link, but of course you don’t have to. I have linked exactly the offers from which I have also bought and was satisfied with the supplier and the goods. The products can of course be bought anywhere.

Microsoft Outlook – Cannot delete this folder

After restoring an Exchange mailbox and sorting the mails, I wanted to delete the restore folder, but Outlook won’t let me:

Cannot delete this folder. Right-click the folder, and then click Properties to check your petmissions for the folder, See the folder owner or your administrator to change your permissions, Shared folders cannot be deleted during synchronization with the server. Delete the folder after synchronization is finished

Solution: Move the folder to trash and then delete the folder.

Mikrotik RouterOS WireGuard dynamic DNS endpoint refresh

MikroTik RouterOS doesn’t yet support DNS names for peer entpoints (v7.1.1). As a workaround, you can set the endpoint address using the CLI, but RouterOS will not re-resolve the DNS name. If the IP addresses behind the DNS name change at some point, for example if you use DDNS, the WireGuard tunnel will eventually stop working. As a solution, you can use a script that checks if the peer endpoint address still matches the dns name and if not, updates to the latest ip address of the DNS name.

Script:

Add under System > Scheduler a new script and choose a useful interval.

:local wgPeerComment
:local wgPeerDns

:set wgPeerComment "Peer #1 Comment"
:set wgPeerDns "dns.example.com"

:if ([interface wireguard peers get number=[find comment="$wgPeerComment"] value-name=endpoint-address] != [resolve $wgPeerDns]) do={
  interface wireguard peers set number=[find comment="$wgPeerComment"] endpoint-address=[/resolve $wgPeerDns]
}
Example:

C/C++/Arduino Datatypes

Type Byte Bit Typical Range
boolean 1 8 true/false
char 1 8 -128 to 127
signed char 1 8 -128 to 127
unsigned char 1 8 0 to 255
byte 1 8 0 to 255
uint8_t 1 8 0 to 255
int 2 16 -32,768 to 32,767
short 2 16 -32,768 to 32,767
signed int 2 16 -32,768 to 32,767
unsigned int 2 16 0 to 65,535
word 2 16 0 to 65,535
uint16_t 2 16 0 to 65,535
long 4 32 -2,147,483,648 to 2,147,483,647
float 4 32 -3.4028235E+38 to 3.4028235E+38
unsigned long 4 32 0 to 4,294,967,295
uint32_t 4 32 0 to 4,294,967,295
uint64_t 8 64 0 to 18,446,744,073,709,551,615

Useful ffmpeg commands

Trim/Cut/Splitt Video

ffmpeg -i input.mp4 -c copy -ss 00:05:00 -to 00:10:00 output.mp4
-c copy Copy all streams
-ss Start time offset
-to Transcode stop time

(re)encode Video with h.254 and AAC

ffmpeg -i input.mp4 -vcodec h264 -acodec aac output.mp4
-vcodec h264 Encodes video to h264
-acodec aac Encodes audio to aac

Resize Video to 1280×720 with high quality settings

ffmpeg -i input.mp4 -vf scale=1280:720 -preset slow -crf 18 output.mp4
-vf scale=1280:720 Set video filter to resize to 1280×720
-crf 18 Constant Rate Factor. A lower value means higher quality

Convert only Audio. EAC3 to AC3 for Example

ffmpeg -i "input.mkv" -map 0 -c:s copy -c:v copy -c:a ac3 output.mkv
-map 0 Selects all streams. Otherwise only one stream per stream type will be selected.
-c:s copy Copy all subtitles.
-c:v copy Copy all video.
-c:a ac3 Encodes all audio to AC-3.

Sporadic freezing/loss of WiFi connection on a Raspberry Pi 3B+

I have two identical Raspberry Pi 3B+ (RPi3B+) running OctoPrint to control my two 3D printers and provide a livestream of the connected webcams when needed. A few months ago I noticed that the “newer” of the two RPIs sporadically lost the WiFi connection after a few minutes or hours. To check if its a a hardware problem I swapped the SD cards between both PIs, but the problem moves with the SD Card, which means its a software problem. First attempts:

  • Update system (dist-upgrade)
  • Changes the location of the Pi to ensure that the WiFi signal is better.
  • A WiFi reconnect script i used before with a Raspberry Zero W.
  • Disabled Power Management with ´sudo iwconfig wlan0 power off´

I have connected a LAN cable, waited until the connection was interrupted and tried various commands to restore the connection. Unfortunately nothing helped. I found some errors in the syslog like mailbox indicates firmware halted and some GitHub issues from RaspberryPi, but no final solution:

wlan freezes in raspberry pi 3B+
PI 3B+ wifi crash, firmware halt and hangs in dongle
brcmfmac: brcmf_sdio_hostmail: mailbox indicates firmware halted

Then I continued to search for differences between the two PIs and found out that the “working Pi” had older drivers 7.45.154 that the “problem Pi”, who had 7.45.229. I downgraded the firmware to 7.45.154 (/lib/firmware/brcm – my older Pi had these files) and disabled power management. Now, after some weeks of 8h printing each and enabled webcam no problems. With 7.45.229 and also disabled power management it freezes. The firmware files were the only thing I changed.

Working WiFi Firmware/Driver:

dmesg | grep brcmfmac
Firmware: BCM4345/6 wl0: Feb 27 2018 03:15:32 version 7.45.154 (r684107 CY) FWID 01-4fbe0b04

Final solution (tl;dr):

  1. Disabled Power Management with ´sudo iwconfig wlan0 power off´
  2. Downgrade drivers/firmware (brcm_7.45.154.tar to /lib/firmware/brcm)

Configure local Systemd-resolved DNS Resolver for Company Domains behind VPN

To send queries for the company internal (sub)-domains to the company DNS resolvers behind the VPN, the resolver can be configured with the following commands:

# Configure internal corporate domain name resolvers:
resolvectl dns tun0 192.0.2.53 192.0.2.54

# Only use the internal corporate resolvers for domain names under these:
resolvectl domain tun0 "~example.com"

# Not super nice, but might be needed:
resolvectl dnssec tun0 off

Calculate series resistor for 0805 SMD LEDs with different colors

When I plan SMD LEDs for one of my PCB designs, I always ask myself which series resistors I need. At AliExpress dealer CHANZON Official Store I found the following nice overview. The series resistor can then be calculated with hte LED Resistor Calculator.