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This Is Where I Draw The Line

Thu, 25 Dec 2025 00:00:01 +0100

So I’ve had a pen plotter for quite a while now. It has shown up a few years back in a post on this site, where I used it for its intended purpose—recording X–Y curves. This plotter is quite a beast, it’s big (up to DIN A3) and heavy, and it’s unlike the majority of vintage plotters you’ll see people using online. This HP 7045A is fully analogue, which means it takes an X voltage and a Y voltage and directly controls the axis motors with analogue servo loops. In fact, it’s more correctly referred to as a recorder, rather than a plotter, since its purpose is to record measurement charts.

Charlieplexing Nixie Drivers

Sun, 10 Aug 2025 15:37:15 +0200

Nixies are great. Delightfully simple in their principle of operation and absolutely unmistakable in their aura. The hard-to-imitate aesthetics do come at a cost: they are a bit inconvenient to drive from modern electronics.

Many tried-and-proven nixie driver circuits can be found online. Using the classic 74141. With individual high-voltage transistors and shift registers. Or multiplexing the nixies to save on driver electronics? Multiplexing of nixies is a controversial topic: while the benefits are clear, many argue that nixies wear out faster due to the high current peaks when multiplexed.

This post isn’t about nixie multiplexing, though.

Lithium Battery Protection for Small Projects

Tue, 24 Jun 2025 20:17:57 +0200

Lithium cells haven’t become the predominant power source for mobile electronics without reason. Circuits for their—very necessary—protection are naturally plentiful as well.

One particular weak point of many protection schemes, however, is deep discharge protection. Common practice is to discharge LiPo/LiIon cells no further than 3 V to not risk permanent damage. Yet, most protection ICs cut off only at 2.5 V, and you thus have to rely on additional battery voltage monitoring.

Es ist Mittwoch.

Wed, 07 May 2025 00:00:00 +0200

Sometimes blog posts just have to sit in the drafts for a while. This one had the opportunity to mature for about a year. The actual project lies back about two and half years by now. The pictures I have of it haven’t got any better in the meantime, so I might just as well hit ‘post’ on this split-flap calendar I built for a friend.

Most of the time, it doesn’t do much. Once a day, it advances by one flap and ⅐ of the time, it announces the day of the week, Wednesday.

Zoom H4n Pro Repair

Sat, 25 Jan 2025 23:01:54 +0100

A Zoom H4n Pro audio recorder found its way to me, non-working. Recordings seemed to be silent, but with loud enough input you could just make out some distorted sound in the recording. After (unneccessarily) disassembling it completely, I found out that the power supply of the preamplifier board was sitting at around 0.8 V, which thankfully/boringly turned out to be the only fault in the unit.

USB-C to Micro-USB Adapters

Mon, 01 Apr 2024 20:07:59 +0200

I have a Seek thermal camera, which works by connecting it to a phone and using Seek’s app to display the image, take photos, etc. It’s an older model, from back when there were two variants, one with Micro-USB and one with Lightning. I’m on my third phone since I got it, which does not have a Micro-USB port any more. But it’s easy to get an adapter from USB-C, right?

Please Do Not Water This Tree

Sun, 04 Oct 2020 22:30:25 +0200

About two years ago, I made a little LED tree as a gift. An extremely simple design with 17 white 0603 LEDs soldered to magnet wire, twisted and bent to make branches, and combined them to a small LED bonsai. Electrically, all LEDs are wired in parallel and connected to 4.5 V via an LDR. This lets the tree react to the ambient brightness and helps it to great battery life.

A Better STM32F0 Prototyping Experience

Mon, 03 Feb 2020 21:04:32 +0100

This project started when I was particularly annoyed by existing development board options and cheap Chinese PCB prototyping services were starting to emerge. Thus, the path forward was clear, but let’s start with the problems I was trying to solve.

When I’m talking about ‘development boards’, I mean boards like the Teensy models, Feather variants or blue pill: a PCB based laid out around a microcontroller containing very little extra circuitry; a ‘least common denominator’ of typical projects using that MCU, if you will. Evaluation boards with more interesting circuitry are great to get used to a microcontroller and its peripherals but lie beyond the scope of this post.

ESP8266 Programmer

Sat, 18 Jan 2020 21:20:21 +0100

For the software side of some ESP8266 development, I bought a cheap ESP01 to USB adapter from AliExpress, expecting a programming adapter. What turned up on my doorstep, however, was just a USB-UART adapter which wasn’t able to drive the reset and GPIO0 pins. Luckily, the missing circuitry could be added easily.

Using Desoldering Braid Bobbins for Bodge Wires

Thu, 26 Dec 2019 19:01:02 +0100

Don’t throw spent desoldering braid spools away! The bobbins are great for hand wiring prototypes and doing PCB repairs. They have the perfect size, and unlike a regular spool, the magnet wire won’t uncoil itself all the time.

Breadboard Test Points

Mon, 18 Nov 2019 13:33:09 +0100

Take a piece of wire, solder one end into a loop and the other one onto a header pin and you’ve got a very useful test point for breadboarding. A piece of shrink tubing shrunk only on one end nicely insulates connected probe hooks and an extra shrink tubing ring around the breadboard end keeps this cover from sliding off.

Building a Camera with a Rather Undersized Microcontroller

Fri, 24 Aug 2018 13:25:00 +0200

Disclaimer: This project was hacked together more or less in a weekend. Not much documentation is available besides the source code. If you want to build this (in the off-chance that you got your hands on one of these printer modules), you’d have to extract the schematic information from pinning.h and supply your own stepper motor driver and level shifter circuit.

I had these thermal printer modules, 4 of them, after I bought them because they were cheap and seemed interesting. For years they physically were somewhere in a drawer; in my mind though, they were taunting me. Something had to be done!

A short reflection on direct laser PCB printing

Mon, 25 Dec 2017 20:39:29 +0100

I have been using a Lexmark E360d laser printer modified for depositing toner as an etch resist directly to PCB material for a while now. Details about the build have already been available on the project’s git repository, and this I’d like to focus on some comments on the actual usefulness of the project. PCB manufacture has been decreasing in its price, so I rarely use the ‘haxmark’ any more. It gets reactivated when I need a board fast and then it still does a decent job.

Arachnouphobia

Fri, 20 Jan 2017 22:22:41 +0100

Catchy title aside, this one is actually about deterring spiders. This small project started with my mother’s observation that a corner of her basement was spider-free since I had set up a NAS there. Rather than assuming that the vibrations/noises generated by the hard drive put the spiders off (like I would), she made a connection the Banana Pi’s irregularly flashing LEDs. That had to be investigated.

Pb Power bank

Sat, 04 Jun 2016 16:33:07 +0200

In preparation for being off-grid for a few days, I quickly built this ‘power bank’ around a 12 V 7 Ah lead gel battery. The circuit is simply pushed onto the battery’s 6.3 mm contacts and provides 3 USB ports. Charging circuitry is not included but the battery terminals are still accessible anyway.

Quick and Dirty B--H Plots

Mon, 21 Sep 2015 15:55:30 +0000

While building solenoids, I needed a way to quickly judge the magnetic properties of some unknown steel. A simple analogue hall sensor IC works together with a controlled current source for the coil to drive a XY plotter (or oscilloscope in XY mode) and create simple B–H plots.

RS232 Wiretap

Sun, 08 Mar 2015 13:41:55 +0100

If you need to monitor a RS232 line (or something else running through a D-Sub connector), use one of these open-style connectors. Their pins fit into a female D-Sub connector and provide ample space to attach probes.

PCB Etching Thermostat

Sat, 13 Dec 2014 16:01:01 +0100

A small thermostat I built for a sodium persulfate PCB etching bath, controlling a heater originally intended for fish tanks (with the original temperature control removed). The temperature is fixed to 45–50 °C and power is provided for a small air pump. Schematics can be found here, PCB design files and MCU firmware here.

Thermocouple via Integrated Differential Amplifier

Sat, 26 Jul 2014 18:38:13 +0100

Recently, I needed a simple temperature switch which could withstand 400 °C. A thermocouple can easily manage this but its generated voltage is unpleasantly small. However, it turns out that a ATTiny216A’s integrated differential amplifier is absolutely sufficient for a, albeit not very accurate, measurement. Enough to determine if something is hot or not, at least.

Philips PM 3265 Repair

Fri, 23 May 2014 15:12:09 +0100

This post was the first post of my first attempt at a blog (which was never published). Albeit I since re-wrote it completely, I decided to keep its original date, which consequently now predates the date this site went online.

I still like analogue scopes. Although the convenience of a digital scope’s features is hard to be matched, I still like to come back to the older world from time to time. Why? I have yet to meet a DSO which is as satisfying to operate as even a basic analogue scope. On a DSO, no matter the price point, you always notice there’s software handling your input, given the ever so slight lag. Not to mention the overall haptics; rotary encoders and rubber push buttons just don’t compare to the real deal.

Milliohm Meter Test Fuchs MOM1

Wed, 14 Aug 2013 18:26:12 +0200

While restoring a milliohm meter made by Test Fuchs I could not find any information about, I traced its schematic. It can be found here in case anyone has the same instrument.

IGBT Chopper

Sun, 06 Nov 2011 22:42:09 +0100

A useful thing to have for testing high voltage transformers is a simple chopper. This one switches a 600 V IGBT with an adjustable frequency between 50 Hz and 29 kHz (lower frequencies are possible with an external timing capacitor) and any duty cycle between 0 and 100%.