Electronics on Charlie Howlett

Jar Light Display

Tue, 28 Jul 2026 00:00:00 +0000

Almost every night I light a candle before going to bed as part of my nighttime routine, so I have heaps of leftover glass jars that seem too nice to throw away. Last weekend my girlfriend and I had the idea to turn one into a nice-looking enclosure for an interactive LED light project.

The first step was cleaning out the old wax and wick.

Next, we made a display that exactly fits the unique shape of the jar. We bought a strip of individually addressable LEDs, cut it into shorter sections, and wired them together into a flexible circular matrix.

Reverse Engineering Roland TM-2

Fri, 19 Jun 2026 00:00:00 +0000

While building my compact hybrid drumming rig, I became very familiar with the Roland TM-2. The module has an enormous number of settings and even lets users save configurations to an SD card as .TM0 files. One day, I opened one of these files on my computer to see what was inside. I found mostly unreadable raw binary data, with a short string of plain English text at the top: the name of my save file. This led me to wonder whether I could reverse engineer the format and display all the information in a web-based user interface.

Building a Raspberry Pi Server Rack

Fri, 12 Jun 2026 00:00:00 +0000

I had three old Raspberry Pis and an SSD sitting unused in a cupboard, so I decided to turn them into a small cluster of home servers. I wanted the finished setup to be compact and tidy enough to live on a little shelf in my television stand, rather than becoming another loose collection of boards, cables, and power adapters tucked away in some cupboard.

For the chassis, I joined two 12-inch server rack trays using a pair of small rack-mounting posts. This was cheaper than buying a premade desktop rack and gave me a reusable foundation: if I later expand the cluster or move it into a larger rack, the trays and mounting hardware can become part of the new setup.

Repurposing a Laptop as a Home Server

Fri, 22 May 2026 00:00:00 +0000

I was recently given an old laptop that had been retired by my company. Despite no longer being needed for work, it still had quite capable hardware, so I decided to repurpose it as a compact, general-purpose home server rather than let it go unused.

Because the server will remain plugged in, I removed the battery to reduce unnecessary heat and avoid leaving an ageing battery permanently charging. I also removed the display, which improved airflow, made the machine easier to fit into tight spaces, and left the power button accessible without needing to open and close a lid. I saved the screen so it can be reused in a future project.

Upgrading a Seiko DM-20 Audio Jack

Sun, 12 Apr 2026 00:00:00 +0000

Recently, I found a Seiko DM-20 digital metronome in a nearby second-hand electronics shop. I really like its compact, thin design and retro appearance, and thought it would be useful during band rehearsals where I often have to bring a much larger metronome.

The only problem was its 2.5mm headphone socket. Most modern headphones and audio cables use a 3.5mm connector, and although an adapter would have worked, it would also have added another small component that could be lost or fail during a rehearsal. I decided to replace the socket so the metronome could connect directly to the equipment I already use.

Building an Arduino Robot Car in a Day

Wed, 12 Jun 2024 00:00:00 +0000

I set myself a small challenge: build a working Arduino robot car in a single day, using only electronics parts I already had around the flat.

I decided to build it because I had found a TB6612FNG motor driver lying around, along with an Arduino Mini, a battery pack, and a couple of small wheels with DC motors. For the body, I used a little wooden board I had spare and fixed the motors and other parts to it with some metal joinery pieces.

Arduino LoRa Monitoring System

Tue, 11 Jan 2022 00:00:00 +0000

I rent a small drumming practice space that I share with several other musicians on a timetable basis. I built this monitoring system to understand how often people were using their booked time slots and how the room’s environmental conditions changed over time. Since the space has no Wi-Fi and unreliable mains power, the project became an interesting challenge involving low-power hardware, long-range radio communication, and remote data collection.

Sensor node

The sensing node is built around a 3.3V Arduino Pro Mini with sensors for PIR motion, humidity, temperature, and ambient light. Every ten minutes, it wakes up, collects readings, packs them into a small JSON payload, transmits the result by radio, and returns to sleep. I spent a significant amount of time reducing its power consumption so the device could run for roughly six months from three AA batteries. For this project, reliable long-term monitoring mattered more than collecting readings more frequently.

Llama Bot

Sat, 01 Jan 2022 00:00:00 +0000

This project started with a burst stress toy llama that seemed too good to throw away. I decided to give it a second life as a singing, dancing robot, which turned a cute toy into a compact embedded engineering project involving electronics, power, motion, and control logic.

Implementation

The electronics were built around an Adafruit Feather HUZZAH ESP8266, with a servo for movement, a buzzer for playing songs, and a rechargeable LiPo battery connected to the board’s micro-USB charging port. I also added an on/off switch by grounding the ESP8266 enable pin, allowing the toy to draw effectively no current while switched off instead of slowly draining the battery. Inside the llama, a structure made from cardboard, copper wire, and hot glue held the components in place and made the damaged toy sturdy enough to survive repeated movement.

Automating Lights with a Raspberry Pi

Thu, 02 Sep 2021 00:00:00 +0000

Pi Lights was a fairly simple idea and my first exploration into DIY home automation: measure the ambient light level throughout the day using a Raspberry Pi, then switch Wi-Fi lights on or off automatically.

Implementation

The system polls several light-dependent resistors and averages their readings before deciding whether to switch the lights. Using multiple sensors and rate-limiting changes made the automation less sensitive to brief shadows or sudden changes in brightness. A dedicated light-sensing Raspberry Pi HAT would have been more accurate, but I wanted to see if I could build a first pass using components I already had lying around. I ran the software as a Linux service so it would start automatically and continue working in the background without needing any attention.

Raspberry Pi Digital Lock

Fri, 02 Nov 2018 00:00:00 +0000

This first-year group project started with a simple brief: build a keypad-controlled digital lock using a Raspberry Pi. It was a small project, but a very rewarding one, and it introduced me to some great people. Ultimately, our project was chosen by the lecturer to be demonstrated at subsequent university open days.

The main constraint was that we were not allowed to rely on interrupt-driven input for the membrane keypad. Instead, we had to detect key presses by polling the Pi’s pins and working through the keypad matrix ourselves. On top of the basic four-digit passcode entry, we added status LEDs for correct and incorrect codes, a short delay after failed attempts to make brute forcing less practical, and a text-based interface for changing settings after the user had gained access. We also wrote software to attack our own system by generating electrical signals that mimicked key presses.