raspberrypi

Ratchet Adapter

I want to electrically drive this ratchet mechanism to avoid the manual labour of turning it by hand. I found a motor with a 1600:1 gearbox on eBay (shipping from China of course) which looks perfect, however it has a 10mm diameter keyed output shaft which doesn’t nicely couple to my 3/4” square ratchet shaft.

Audio Stream from a Raspberry PI

Now singing has returned to churches I need to add an additional microphone to pickup the choir. I’d like this to be completely separate to the Church PA system to avoid playing this sound out through the speakers. A Raspberry PI Zero W with a USB sound card looks to be a good option to capture the audio and stream it to OBS.

Mini ITX as Windows 2008 Server

Unfortunately without a DVD drive and with no capability to boot from USB I’m struggling to get a clean OS on my Mini ITX machine. The internal drive is IDE and I don’t have any other machines with IDE around and I don’t know the password for the installed OS.

Raspberry PI Camera with M12 Lens

I really need a good lens on my Raspberry PI camera to use it with OBS from a decent distance. The new high resolution Rasperberry PI cameras look excellent but they also come with a heafty price tag which I just can’t justify.

Normalise MP3 Files

I have hundreds for MP3 files but the levels aren’t standardised in any way which makes streaming them a bit hit and miss. I can normalise them using AudaCity but I’d really like an automatic way of doing it.

TEMPer USB Temperature Sensor

These USB sensors are available pretty cheaply from PiHut and Amazon and are great for monitoring the temperature remotely (where you have a Pi).

Raspberry PI as RTSP source for OBS using VLC

Using the new Raspberry Pi Imager I’ve installed the latest Raspberry Pi OS Lite (32 bit).

Netatalk on a Raspberry PI

Using the Raspberry PI imager application copy the Raspberry PI OS Lite to an SD card. Then remove and reinsert the card.

Raspberry PI as RTSP source for OBS

Using the new Raspberry Pi Imager I’ve installed the latest Raspberry Pi OS Lite (32 bit).

Music Library

Using a Raspberry PI with a USB CD drive to read all my CDs and create a master, FLAC format, repository and from that create MP3 and AAC versions for the car and iTunes.

OLED Module for PI

Run raspi-config and turn on the i2c interface

Bridged WiFi Access Point with Raspberry Pi

Run ifconfig and determine your network device names. Typically these will be eth0 and wlan0.

Raspberry PI SSH Keys

This is my cheatsheet based upon Passwordless SSH access on the official Raspberry PI website.

Raspberry PI Zero W Headless setup

Copy 2019-07-10-raspbian-buster-lite.img to the SD card with Etcher. Then remove and reinsert the card.

Internet Radio from Raspberry PI

Install the software packages needed

Retro Gaming: Space Raiders

Dylan’s favourite t-shirt is his Game Over shirt which always reminds me to Space Raiders from the ZX Spectrum days. I found the cassette tape quite easily but it took a significant amount of searching to find the Spectrum itself and included in the box was the tape recorder as well!

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OCaml

Blade Server Reallocation

We have changed our mind about using dm-cache in the SSD/RAID1 configuration. The current thinking is that the mechanical drives would be better served as extra capacity for our distributed ZFS infrastructure, where we intend to have two copies of all data, and these disks represent ~100TB of storage.

OCaml Infra Map

Yesterday, we were talking about extending the current infrastructure database to incorporate other information to provide prompts to return machines to the pool of resources after they have completed their current role/loan, etc. There is also a wider requirement to bring these services back to Cambridge from Equinix/Scaleway, which will be the subject of a follow-up post. However, the idea of extending the database made me think that it would be amusing to overlay the machine’s positions onto Google Maps.

Blade Server Allocation

Equinix has stopped commercial sales of Metal and will sunset the service at the end of June 2026. Equinix have long been a supporter of OCaml and has provided free credits to use on their Metal platform. These credits are coming to an end at the end of this month, meaning that we need to move some of our services away from Equinix. We have two new four-node blade servers, which will become the new home for these services. The blades have dual 10C/20T processors with either 192GB or 256GB of RAM and a combination of SSD and spinning disk.

Topological Sort of Packages

Given a list of packages and their dependencies, what order should those packages be installed in?

Recent OCaml Versions

Following my post on discuss.ocaml.org, I have created a new release of ocurrent/ocaml-version that moves the minimum version of OCaml, considered as recent, from 4.02 to 4.08.

Real Time Trains API

After the Heathrow substation electrical fire, I found myself in Manchester with a long train ride ahead. Checking on Real Time Trains for the schedule I noticed that they had an API. With time to spare, I registered for an account and downloaded the sample code from ocaml-cohttp.

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obs

Ratchet Adapter

I want to electrically drive this ratchet mechanism to avoid the manual labour of turning it by hand. I found a motor with a 1600:1 gearbox on eBay (shipping from China of course) which looks perfect, however it has a 10mm diameter keyed output shaft which doesn’t nicely couple to my 3/4” square ratchet shaft.

Audio Stream from a Raspberry PI

Now singing has returned to churches I need to add an additional microphone to pickup the choir. I’d like this to be completely separate to the Church PA system to avoid playing this sound out through the speakers. A Raspberry PI Zero W with a USB sound card looks to be a good option to capture the audio and stream it to OBS.

Mini ITX as Windows 2008 Server

Unfortunately without a DVD drive and with no capability to boot from USB I’m struggling to get a clean OS on my Mini ITX machine. The internal drive is IDE and I don’t have any other machines with IDE around and I don’t know the password for the installed OS.

Raspberry PI Camera with M12 Lens

I really need a good lens on my Raspberry PI camera to use it with OBS from a decent distance. The new high resolution Rasperberry PI cameras look excellent but they also come with a heafty price tag which I just can’t justify.

Raspberry PI as RTSP source for OBS using VLC

Using the new Raspberry Pi Imager I’ve installed the latest Raspberry Pi OS Lite (32 bit).

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OCaml

Blade Server Reallocation

We have changed our mind about using dm-cache in the SSD/RAID1 configuration. The current thinking is that the mechanical drives would be better served as extra capacity for our distributed ZFS infrastructure, where we intend to have two copies of all data, and these disks represent ~100TB of storage.

OCaml Infra Map

Yesterday, we were talking about extending the current infrastructure database to incorporate other information to provide prompts to return machines to the pool of resources after they have completed their current role/loan, etc. There is also a wider requirement to bring these services back to Cambridge from Equinix/Scaleway, which will be the subject of a follow-up post. However, the idea of extending the database made me think that it would be amusing to overlay the machine’s positions onto Google Maps.

Blade Server Allocation

Equinix has stopped commercial sales of Metal and will sunset the service at the end of June 2026. Equinix have long been a supporter of OCaml and has provided free credits to use on their Metal platform. These credits are coming to an end at the end of this month, meaning that we need to move some of our services away from Equinix. We have two new four-node blade servers, which will become the new home for these services. The blades have dual 10C/20T processors with either 192GB or 256GB of RAM and a combination of SSD and spinning disk.

Topological Sort of Packages

Given a list of packages and their dependencies, what order should those packages be installed in?

Recent OCaml Versions

Following my post on discuss.ocaml.org, I have created a new release of ocurrent/ocaml-version that moves the minimum version of OCaml, considered as recent, from 4.02 to 4.08.

Real Time Trains API

After the Heathrow substation electrical fire, I found myself in Manchester with a long train ride ahead. Checking on Real Time Trains for the schedule I noticed that they had an API. With time to spare, I registered for an account and downloaded the sample code from ocaml-cohttp.

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Ubuntu

Ubuntu cloud-init with LVM and dm-cache

dm-cache has been part of the mainline Linux kernel for over a decade, making it possible for faster SSD and NVMe drives to be used as a cache within a logical volume. This technology brief from Dell gives a good overview of dm-cache and the performance benefits. Skip to the graph on page 25, noting the logarithmic scale.

Gluster

Gluster is a free and open-source software network filesystem. It has been a few years since I last looked at the project, and I was interested in taking another look. Some features, like automatic tiering of hot/cold data, have been removed, and the developers now recommend dm-cache with LVM instead.

Ubuntu cloud-init

Testing cloud-init is painful on real (server) hardware, as the faster the server, the longer it seems to take to complete POST. Therefore, I highly recommend testing with a virtual machine before moving to real hardware.

Jitsi

I need to remotely control OBS during a live stream. This is quite simply achieved via VNC but I need the see and hear what’s going on at the same time. VNC doesn’t support audio on the free license and watching the YouTube stream is out of the question as it’s nearly 30 seconds behind real time.

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bells

Internet Radio from Raspberry PI

Install the software packages needed

Most Popular Methods

There are ~72,000 Surprise Major performances on Bell Board. Bell Board displays results in pages of 200 performances. Thus we will need to download all the pages and concatenate them into a single file:

Splicing Three Strand Rope

My sudden interest in rope splicing stems entirely from bell ropes. There seems to be three, perhaps four, splices to learn for this application. Links below to YouTube videos explaining how to do them:

Place Notation

Thomas Barlow has taught me place notation using Strike Back Surprise Major as the example. The notation for that is x38x14x58x16x12x38x14.12.78 l.e. 12. There are plenty of guides online on how to interpret it, such as this one on the CCCBR website.

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perl

Place Notation

Thomas Barlow has taught me place notation using Strike Back Surprise Major as the example. The notation for that is x38x14x58x16x12x38x14.12.78 l.e. 12. There are plenty of guides online on how to interpret it, such as this one on the CCCBR website.

Shape Files

Below is a perl script to create a PNG from a Shape file.

Mandelbrot Set

The Mandelbrot set is created from this very simple formula in which both Z and C are complex numbers.

Narcissistic Numbers

I heard about these on BBC Radio 4 More or Less and they just intrigued me, perhaps in part because they have no known application! In the past similar obsessions have appeared with the calculation of PI and right back to my childhood calculating powers of 2 on a BBC Micro.

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powershell

PowerShell SNMP

Potentially, I’ve got a bit carried away here. There isn’t a native PowerShell module to query SNMP which I found a bit surprising. How hard could it be? I’ve got a SYSLOG server and client in PowerShell so this felt like a simple extension. The SNMP client needs to send a request over UDP to the SNMP server on port 161 and waits for the response back. Sending via .NET’s UDPClient is easy enough

Mount an ISO from your Desktop via PowerCLI

Normally, I’d used a Windows NFS Server to host my ISO files. The steps couldn’t be simpler

Which Funds Have Exposure to NetFlix?

Dabbling in the markets by way of investment funds is amusing. I use Hargreaves Lansdown to do this. HL have a fund research section which lets you look at a given fund and view the top 10 holdings so you can base your decision to invest in your belief in the underlying stock.

Prime Numbers in PowerShell

Dylan was using a number square to calculate prime numbers so it amused me to code up a couple of algorithms to show just how quick the sieve method actually is. I’ve done these in PowerShell because … reasons.

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Box

Box Diff Tool

Over the weekend, I extended mtelvers/ocaml-box-diff to include the ability to upload files over 50MB. This is a more complex API which requires a call to https://upload.box.com/api/2.0/files/upload_sessions by posting JSON containing the name of the file, the folder ID and the file size. Box replies with various session endpoints which give the URIs to use to upload the parts and to commit the the file. Box also specifies the size of each part.

Box API with OCaml and Claude

Over the weekend, I decided to extend my Box tool to incorporate file upload. There is a straightforward POST API for this with a curl one-liner given in the Box documentation. Easy.

Box Diff Tool

Box has an unlimited storage model but has an upload limit of 1TB per month. I have been uploading various data silos but would now like to verify that the data is all present. Box has an extensive API, but I only need the list items in folder call.

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juniper

How To GitHub

I really don’t use GitHub often enough to remember the commands without searching for them each time, which means that I use GitHub even less as I can’t remember the commands. Here’s a short cheat sheet on the most common things I need to do in GitHub.

Bose SoundTouch and Mini DLNA

Bose have a Windows application can host your music library, however I don’t have a Windows machine turn on permanently and I’d prefer a low power Raspberry PI option.

Juniper SRX100 Firmware Update

Download the latest version of the software and copy it over to the SRX

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3d-printing

Arduino PWM Train Controller

Circuit

3d Printed Train

Creating a new OO train body drawn from scratch in Fusion 360 to minic the original damaged version.

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Dell

More Kingston Drives

We have received the second batch of 40 x 7.68TB Kingston SSD drives, bringing the total to 50 drives.

Dell PowerEdge R640 Storage Server

We have received our first batch of 7.68TB Kingston SSD drives for deployment in some Dell PowerEdge R640 servers, which will be used to create a large storage pool.

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Dell

More Kingston Drives

We have received the second batch of 40 x 7.68TB Kingston SSD drives, bringing the total to 50 drives.

Dell PowerEdge R640 Storage Server

We have received our first batch of 7.68TB Kingston SSD drives for deployment in some Dell PowerEdge R640 servers, which will be used to create a large storage pool.

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R640

Dell R640 Ubuntu Installation

I could have scripted this via Ansible, but there would always be a manual element, such as configuring the H740P controller and booting from the network to get to the point where you can SSH to the machine. Therefore, I decided to just document the steps required.

Dell R640 installation

Today we have racked the five 14th generation Dell R640 servers and a Dell N4032 switch.

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arduino

Foot Operated Timer

At the end of a quarter peal there is always the question of how long it took and whether anyone really noted the start time. Mike proposed a foot operated timer.

Arduino Gas Sensor

With the current emphasis on ventilation to reduce the risks associated with inhaled droplets it I have put together a simple gas sensor to record concentrations over time. The output is a CSV file which can be graphed in Excel.

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bash

Dump Process Memory

Yesterday in a stroke of good fortune, I remembered a job that I’d set running a little while back and I checked in to see how it was doing. It’s a MPI console app running on 22 distributed Ubuntu nodes. My application was set to output the time periodically and it currently reported a runtime of 15837421 seconds (just over six months). Unfortunately I couldn’t see the current ‘best’ result as it results aren’t displayed until the end. I was intrigued to see how it was doing.

Most Popular Methods

There are ~72,000 Surprise Major performances on Bell Board. Bell Board displays results in pages of 200 performances. Thus we will need to download all the pages and concatenate them into a single file:

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bluesky

Setup Tangled with Bluesky

To setup this up, I’m using a modified version of Anil’s repo. My repo is here. Firstly, clone the repo and run gen-key.sh.

Bluesky Personal Data Server (PDS)

Today I have set up my own Bluesky (PDS) Personal Data Server.

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bluesky

Setup Tangled with Bluesky

To setup this up, I’m using a modified version of Anil’s repo. My repo is here. Firstly, clone the repo and run gen-key.sh.

Bluesky Personal Data Server (PDS)

Today I have set up my own Bluesky (PDS) Personal Data Server.

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opam

opam repo ci job timeouts

It’s Tuesday morning, and virtually all opam repo ci jobs are failing with timeouts. This comes at a critical time as these are the first jobs following the update of ocurrent/ocaml-version noted on 24th March.

Installation order for opam packages

Previously, I discussed the installation order for a simple directed acyclic graph without any cycles. However, opam packages include post dependencies. Rather than package A depending upon B where B would be installed first, post dependencies require X to be installed after Y. The post dependencies only occur in a small number of core OCaml packages. They are quite often empty and exist to direct the solver. Up until now, I had been using a base layer with an opam switch containing the base compiler and, therefore, did not need to deal with any post dependencies.

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openzfs

Distributed ZFS Storage

Following Anil’s note, we will design and implement a distributed storage archive system for ZFS volumes and associated metadata. Metadata here refers to key information about the dataset itself:

Ubuntu with ZFS root

The installation of Ubuntu on ZFS contains about 50 steps of detailed configuration. I have 10 servers to install, so I would like to script this process as much as possible.

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sshd

Bluesky SSH Authentication #2

Addressing the glaring omissions from yesterday’s proof of concept, such as the fact that you could sign in as any user, you couldn’t revoke access, all hosts had the same users, and there was no mapping between Bluesky handles and POSIX users, I have updated mtelvers/bluesky-ssh-key-extractor and newly published mtelvers/bluesky-collection.

Bluesky SSH Authentication

If you have sign up to tangled.sh you will have published your SSH public key on the Bluesky ATproto network. Have a browse to your Bluesky ID, or mine. Look under sh.tangled.publicKey.

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ubuntu

Hard disk failure

Check the status with sudo mdadm --detail /dev/md0

Minecraft Java Edition Server on Ubuntu 18.04

See How to install a Minecraft Bedrock Server on Ubuntu

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Fedora

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FreeBSD

FreeBSD 14.2 Upgrade

CI workers spring and summer run FreeBSD and need to be updated.

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GCC

OCaml < 4.14, Fedora 42 and GCC 15

Late last week, @MisterDA added Fedora 42 support to the Docker base image builder. The new base images attempted to build over the weekend, but there have been a few issues!

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GNU

GNU Parallel

If you haven’t used it before, or perhaps it has been so long that it has been swapped out to disk, let me commend GNU’s Parallel to you.

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Gluster

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Jitsi

I need to remotely control OBS during a live stream. This is quite simply achieved via VNC but I need the see and hear what’s going on at the same time. VNC doesn’t support audio on the free license and watching the YouTube stream is out of the question as it’s nearly 30 seconds behind real time.

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Netboot.xyz

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OpenBSD

Syncthing on OpenBSD

Network Installation of OpenBSD

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Slurm

Slurm Workload Manager

Sadiq mentioned slurm as a possible way to better schedule the group’s compute resources. Many resources are available showing how to create batch jobs for Slurm clusters but far fewer on how to set up a cluster. This is a quick walkthrough of the basic steps to set up a two-node compute cluster on Ubuntu 24.04. Note that slurmd and slurmctld can run on the same machine.

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Syncthing

Syncthing on OpenBSD

Network Installation of OpenBSD

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applescript

Import Text File of events into Apple Calendar using AppleScript

The Church of England has a very useful calendar page, but I’d really like it in my iPhone calendar so I can have reminders for Saints’ days particularly red letter days when the flag goes up.

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c

Pentominoes

One day I was clearing out some old papers and I came across this programming assignment from university. I can’t recall which of the problems I tackled at the time, after all it was twenty-five years ago, but glancing over it now the pentomino problem caught my eye

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c++

Latin Square

Looking at the latest video from Presh Talwalkar about solving the Latin square where each row is the first row multiplied by the row number I decided it was time to see if I could remember any C++ and code a solution.

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capnpproto

Playing with Cap’n Proto

Cap’n Proto has become a hot topic recently and while this is used for many OCaml-CI services, I spent some time creating a minimal application.

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clock

Clock winder repair

The galvanised steel wire rope on one of my clock winders has snapped. This is a 3mm rope, so it would have a rating of greater than 500 kg. I am quite surprised that it snapped, as the load on this wire rope is much lower than that of others in use in the same system.

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cloud-init

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dm-cache

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docker

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flac

Music Library

Using a Raspberry PI with a USB CD drive to read all my CDs and create a master, FLAC format, repository and from that create MP3 and AAC versions for the car and iTunes.

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get.dune.build

Equinix Moves

The moves of registry.ci.dev, opam-repo-ci, and get.dune.build have followed the template of OCaml-CI. Notable differences have been that I have hosted get.dune.build in a VM, as the services required very little disk space or CPU/RAM. For opam-repo-ci, the rsync was pretty slow, so I tried running multiple instances using GNU parallel with marginal gains.

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go

Updating Docker and Go

For some time, we have had issues on Ubuntu Noble when extracting tar files within Docker containers. See ocaml/infrastructure#121. This is only an issue on exotic architectures like RISCV and PPC64LE.

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irmin

Irmin Database

After Thomas’ talk today I wanted to try Irmin for myself.

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jekyll

WordPress to Jekyll Test

Install the Wordpress plugins UpdraftPlus. Create a new WordPress site and install the UpdraftPlus plugin and restore the database.

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maths

Square Root

As a first step in calculating a square root look at the order of magnitude of the number and this will quickly allow the determination of the number of digits in the solution. Consider squaring numbers less than 10; the solutions will be less than 100. Squaring numbers less than 100 gives solutions less than 10,000 and numbers less than 1,000 will square to numbers less than 1,000,000 etc. In general terms the square root of a number with an even number of digits will have half the number of digits as the original number. For numbers with an odd number of digits then the solution will have one more than half the number of digits.

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minecraft

Minecraft Java Edition Server on Ubuntu 18.04

See How to install a Minecraft Bedrock Server on Ubuntu

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ocaml-ci

Moving OCaml-CI

As noted on Thursday, the various OCaml services will need to be moved away from Equinix. Below are my notes on moving OCaml-CI.

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oled

OLED Module for PI

Run raspi-config and turn on the i2c interface

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opam-repo-ci

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osx

Civilization III on OS X

Install Oracle VirtualBox and install Windows XP 32 bit.

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pi

Pi Day - Archimedes Method

It’s Pi Day 2025

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power9

Raptor Talos II - POWER9 unreliability

We have two Raptor Computing Talos II POWER9 machines. One of these has had issues for some time and cannot run for more than 20 minutes before locking up completely. Over the last few days, our second machine has exhibited similar issues and needs to be power-cycled every ~24 hours. I spent some time today trying to diagnose the issue with the first machine, removing the motherboard as recommended by Raptor support, to see if the issue still exists with nothing else connected. Sadly, it does. I noted that a firmware update is available, which would move from v2.00 to v2.10.

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raspberry-pi

Deepseek R1 on a Raspberry Pi

I’ve heard a lot about Deepseek and wanted to try it for myself.

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registry.ci.dev

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snmp

PowerShell SNMP

Potentially, I’ve got a bit carried away here. There isn’t a native PowerShell module to query SNMP which I found a bit surprising. How hard could it be? I’ve got a SYSLOG server and client in PowerShell so this felt like a simple extension. The SNMP client needs to send a request over UDP to the SNMP server on port 161 and waits for the response back. Sending via .NET’s UDPClient is easy enough

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specturm

Retro Gaming: Space Raiders

Dylan’s favourite t-shirt is his Game Over shirt which always reminds me to Space Raiders from the ZX Spectrum days. I found the cassette tape quite easily but it took a significant amount of searching to find the Spectrum itself and included in the box was the tape recorder as well!

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