Category Archives: electronics hobbyist

Articles about handicraft projects on the subject of electronics
for example: a radio with Arduino, Geiger counter …

EVU Smartmeter read out with ESP32 and send data via MQTT


Little by little, I am bringing many of my smarthome components to a common standard. I have decided to bring all devices together via a NodeRed server. The HomeMatic system also communicates with NodeRed. Among other things, I also transfer the measured values of the EVU meter (I have a Siemens IM350 smart meter installed) to the HomeMatic CCU. This is done as mentioned in an earlier post, via the LED pulse interface (1000 pulses/kWh). For this purpose, a phototransistor is simply attached above the LED on the meter, which detects the flashing pulses of the LED and converts them into the instantaneous power in the meter sensor transmitter unit HM-ES-TX-WM and integrates them over time and then sends the data on to the CCU. This works quite well in itself. Only the update rate (in the minute range) is too long for me. Also, the phototransistor seems to react again and again to the stray light of the neighboring LED (which displays the reactive power in 1000 pulses/kvarh). This causes discrepancies between the count via the HomeMatic sensor and the values read directly from the meter.

This is definitely more accurate. If you look at the IM350 Smartmeter meter in detail, or read through the manual, you will quickly see that it has a so-called “customer interface”. This customer interface provides some measurement data via a galvanically isolated data line every second. This includes, among others, the momentary active power in both directions, as well as the meter readings of active and reactive power in the reference and feed-in direction. So perfect starting conditions to replace the HomeMatic meter sensor with my own design. After a little Internet research, I quickly realized that I am not the only one who deals with exactly this issue. The data of the customer interface tumbles out after request over a data request line with a speed of 115kbaud. However, they are encrypted, and not directly readable. To obtain the 16-byte decryption key, the utility must be consulted. The key is tied to the smart meter serial number and is unique to each smart meter. After some phone calls with my Carinthian energy provider, the key code was sent to me by mail. In the next step I tested with a USB-UART adapter on a PC, if data really come out of the meter when the interface is wired correctly. For this I crimped a RJ11 connector to a suitable 6pin cable and wired the open end of the cable according to the datasheet of the meter. Not much is needed for this. A 5V supply must activate the interface, likewise the Data Request line must be switched to 5V and already the data packets are available at the Data Out line. By the way, it also works with a 3V3 supply. With a terminal program on the PC (I usually use putty or hterm) you can visualize the encrypted data.

Now it was time to think about how to decode and process the data. For this, one finds two approaches with net:

* via a RaspberryPi, with a Python environment and a Python script. The scripts here take over the reception and decryption of the data and then make them available for further processing in different ways

* via an ESP32. The ESP is also able to decode a 128Bit AES encryption and still has plenty of resources to process the data and send it via WiFi. Furthermore, an ESP is available in sufficient quantities for little money. So I decided to use this solution. There is an open source project on GitHub from the user in which he provides an ESP32 IM350 decoder as a basis for own projects. With his sources you get a decoder that reads the meter data every second and outputs it via the USB UART programming interface and also via Telnet over WiFi. I used this source as a basis.

My goal is to put the data obtained from the smart meter into MQTT messages and send them to my MQTT broker. From there it is then a simple matter to get them into NodeRed and the HomeMatic CCU and store them there. So I adapted the code. This involved setting the wifi connection to the router to a static IP. (are to be defined in settings.h). The readout readings, as well as the RSSI of the wifi connection, are now provided via MQTT Topics. (the IP address to the broker is also to be defined in settings.h). If you compile the code now and run it on the ESP, then it should log into the respective network. As long as the ESP is still connected to a PC, you can check what it is doing via the programming interface and a terminal. If you now connect the RJ11 plug to the customer interface of the meter, the triangle above the label “KU” should flash in the display of the meter every second. If this happens, the measured values should already be displayed in the terminal (provided that you have not forgotten to enter the KEY from the utility in secrets.h). If this also works, then a look at the MQTT broker (with e.g.: MQTT Explorer) makes sure that the messages arrive. Now the ESP can be removed from the PC.

Connection assignment
ESP32 in “free-flying” test setup

I chose a very simple solution and mounted the ESP on a breadboard. The 6pin cable to the smartmeter is soldered there. On the breadboard there is room for the pull-up resistors and a NPN transistor (BC547 etc.) for inverting the data pulses. I put the board in a small plastic box, which is now only connected with a cable to the customer interface and with a USB cable to a USB power supply.

The finished structure then (or currently) looks like this. The data ends up in the MQTT broker and NodeRed visualizes it and sends it to the HomeMatic CCU.

this is how the data arrives at the MQTT broker
and can be processed in NodeRed like this

if someone is interested in the customized scripts, I can send them to you. Regarding a publication on GitHub, I have to find out first which license conditions have to be fulfilled concerning the original repository. It will then be available here (public):

A rebuild project for the Vectrex


It’s been some time again that I manage to find time and energy in the later evening hours to write here on the blog about one of my little projects. Over the past few years, I’ve gotten into the habit of listening to podcasts during car rides and at night. These primarily include podcasts on technical topics. Among them is a podcast called “Retrokompott” which is about home computers and technology from our youth. Their tagline is:

Retrokompott, eine Zeitreise in die Vergangenheit alter Homecomputer, Spielekonsolen und Games


In one of the contributions of Retrokompott one discussed for some episodes (172-177) about the Vectrex, the home – vector game machine of MBE. Among other things, homebrew projects, i.e. software developments of the users, were presented.  “Vectorblade” is a game title, which was developed by Malban []. The project was created with the Vectrexcompiler (vide), also developed by Malban. The sources are publicly available on the website. In the “compote” article, people were so enthusiastic about Vectorblade that my interest was piqued. The game module was also available for purchase through Malban for a while. However, I have not found a source through which I can easily purchase the module. So I thought, I’ll just rebuild it for myself. The special thing about this gamerom is the size of the game. It has 192 kB. To address this memory, Malban used bank switching technology. He uses a flash memory from SST, the SST39SF020, in his design. The bank switching is controlled by a quad 2-input NAND Schmitt trigger (74AC132). Malban has published on git the layout. There he uses the memory in the DIL package and also the AC132. Detailed instructions can be found here.

Since I still have some boards left over from my old homebuilt Rom module project, I was able to quickly put together a test setup.  I didn’t have any flash memory available – but a sufficiently large EPROM. The video compiler and the source files are also published on Malban’s GIT. After a short study of his vide-compiler I managed to compile the project and create a ROM – file. With my “Far East Programmer” I could then “burn” the EPROM.  With a few wire bridges and an AC132, my old ROM board project then became the Vectorblade experimental setup.

Vectorblade test setup

With the exception that no settings can be saved, the test setup works and the game can be played :). The next step of the rebuild was to draw the PCB. Here I wanted to build in the Schmitt-Trigger device in SMD design and the SST still in DIL. I also realized this design and tested it successfully. But there is a little catch – none of my suppliers has the SST39SF020 flash memory in DIL design in stock. I have now some boards with DIL – layout but no chips… So once again to the PC and redraw the design on PLCC socket. Thought – done and ordered a set of boards from the Far East producer.

A suitable case can be created with the 3D printer itself. To be more precise, I found what I was looking for on Thingiverse and was able to choose from a variety of suitable designs.

The overlay is missing, but the game is fun even without it. Malban has managed to create a great game here.

MIDI DB50XG – an interface for the daughter board


Rummaging through a box of my old crafts I found the box below. It dates from the time when I was still working with Amgia, but also with PCs – I guess around 1996. I labeled the box “DB50XG MIDI – Wavetable Processor”.

Das Fundstück aus der Kiste

Inside is a circuit board from Yamaha, which is called the DB50XG. This board was designed as a daughter board for PC sound cards with “Waveblaster” expansion port. She expanded the sound cards with a polyphonic MIDI wavetable sampler. In this way, the General Midi Standard and the Yamaha XG Standard could be re-established. Today nobody thinks about it anymore. At that time, if you wanted to generate sounds with a PC from midi data, then either external hardware was required, or a sound card with an onboard midi synthesizer or wavetable chipset. The PC then took over the control, the sending and receiving of the midi data via a sequencer software. Today, the midi sounds are generated directly on the PC and the samples and sound models are integrated into the software. At that time, the performance of the PC hardware was not sufficient. If someone is wondering what I’m palavering about here – what is Midi and why do you need it? – then let me put it briefly here: Midi is the abbreviation for “Musical Instrument Digital Interface” – i.e. a digital interface – a data protocol for musical instruments. Roughly explained, it serves to network and control electronic musical instruments with each other. For example, a large number of sound-generating devices can be controlled via a single keyboard. I will not explain here how the Midi standard works, what the data packets look like and how it looks electrically. As always, there is plenty of information on the web.

Inside the box

Back to the self-made box. At that time I packed the DB50XG in the plastic box and from the “Waveblaster” port, a 26-pin socket strip, led the necessary cables to the outside to start up the Midi board. And that was pretty simple. The board requires a power supply of +/-12V and +5V. There is a Midi-IN and a Midi-OUT (through) pin, a reset pin and two analog audio out pins – one per channel. The table below shows the connector pin assignment:

pin number assignment
1 Digital ground
2 not connected
3 Digital ground
4 not connected
5 Digital ground
6 Supply +5V
7 Digital ground
8 not connected
9 Digital ground
10 Supply +5V
11 Digital ground
12 not connected
13 not connected
14 Supply +5V
15 Analoge ground
16 not connected
17 Analogue ground
18 Supply + 12V
19 Analogue ground
20 Audio out richt
21 Analogue ground
22 Supply -12V
23 Analogue ground
24 Audio out left
25 Analogue ground
26 reset

The whole structure was rather spartan back then. The power supply had to be established via one or more external power supplies. There was no galvanic signal isolation using optocouplers. So I had to rely on the proper setup of the Midi IO controller that I connected to the Amiga. Of course it couldn’t stay like this. And I can’t bring myself not to use the beautiful DB50XG board anymore or to throw it away in the electronic waste. The plan that emerged from this was to develop a new interface board – or to tinker, which should be as universally usable as possible.


It’s been a few years since this idea and I’ve always worked on it a little bit. I thought the interface board should fulfill the following points:

  • a simple power supply should supply the Yamaha board with energy. Ideally, there should be a USB port and, optionally, a connection for a universal power supply. All required voltages should be generated on the interface board from the 5VDC.
  • As in the past, the DB50XG should also be able to be plugged in as a “piggyback” circuit board
  • The midi-in signal should be able to be fed in via the 5-pin DIN socket and also via a pin header – of course nicely decoupled (this means that a microcontroller such as Arduino and co. can also be connected without any effort)
  • The sound, i.e. the audio signal, should be available for acceptance via a chinch socket and also as a 3.5mm jack socket and via a pin header per channel.
  • Word repetitions SHOULD be avoided, but I don’t care 🙂

This ultimately resulted in the following circuit diagram. The 5VDC supply of the USB source is routed directly to the 5V supply of the midi board. The +12V/-12V that are also required are generated by a DC/DC converter (TMR0522). This is supplied on the input side by the 5V mains. The optional “external” voltage input goes to a LM2596ADJ. This is a step-down voltage regulator that can work with input voltages up to 40V. The regulated output side is available in many areas. I have integrated the ADJ (Adjustable) type into the circuit here, as I have a few of them in the assortment box. The voltage source can be selected with a jumper on the board.

Based on this circuit diagram, I created a layout and initially produced it in my own etching bath. The result was the following circuit board, which served as a test setup. Technically, the board worked perfectly, but I didn’t like the arrangement of the components. I placed the step-down converter and coil on the back. The distance between the connection sockets was also too close together for me. And how you do it as a PCB layouter – you always do a second design. So also it is this time.

The test setup with a fitted Midiboard can be seen in the image below. The midi signal as a test source comes from the PC and is generated by a USB midi adapter from the Far East.

So sat down in front of the computer again and redrawn the layout. The following version came out. I then ordered this version from a circuit board manufacturer.

The finally manufactured printed circuit board then looks like this. Below she can be seen with the DB50XG board attached.


Selfmade Nixiclock


The fact that the topic of retro has become more and more of a trend in recent years has not escaped me either. The “Industrial” and “Steam” style has also found its way into many households. People put many things on the shelf again, which represent the robust technology and the appearance of the past decades. For example, LED lamps flicker in the rooms, which were visually modelled on the light bulbs of the Wilhelminian era. The brass lamp holders are held in place by a cable sheathed with fabric mesh. Instead of the carbon or tungsten filaments in the bulbs, modern LED filament works. Thematically corresponding to this style, mechanical watches and electric clocks with illuminated displays of all kinds, for example, are in demand again. In keeping with this trend, I have already reported on the VFD watches in older blog posts. (VFD = VaccumFLuoreszenzDisplay) Until the end of the 90s, for example, this display technology was still frequently used in video recorders, hi-fi devices and various radio alarm clocks. After that, LED and LCD technology was standard. Today, the small OLEDs are finding their way everywhere. As part of the Retro Revival, VFDs are assembled into watches in the form of single-digit display tubes. These watches are available as finished devices or as kits ( Since these display tubes are no longer manufactured and only old stocks (new old stock) are available, prices are also rising. But it is even worse in terms of price – a technical development from the 1920s is a display technology based on the principle of the glow lamp. In this case, in a glass flask filled with noble gas, a digit bent from wire is attached as a cathode, in front of a thin metal grid as an anode. If a voltage is applied, the noble gas begins to glow along the wire formed as a digit. Seen from the outside, this creates the impression of a luminous number. In such a tube, the digits from 0-9 are usually accommodated and for each digit there is of course a separate connection. Many of the readers will surely know this type of tube. It is called NIXIE – display tube (comes from the designation “Numeric Indicator eXperimental No. 1”

A watch with such display tubes is still missing in my collection. So I wanted to own one. But buying is easy – and also very expensive. So I decided to build a Nixie clock myself. It all started with a lengthy search for the tubes, because even for these you have to lay down a lot in the meantime. And I need at least six pieces, because my watch should also have a second display. So I searched the Internet on various platforms – and in the bay I found what I was looking for. There a board equipped with Nixie tubes was offered, which was broken out of some old device. The function of the board was given as “unknown” – but it was very cheap. The seller had two of them. So I risked it and bought the two boards equipped with five Nixies each.

The tubes were then successfully soldered out with some caution. The type of tube is the Z574M, for which you can also find the data sheets in the network and thus also has the socket circuitry.

With the help of the wiring, it can then be easily contacted and thus check digit by digit of each tube. The characteristics of the 574 are:

  • Anode ignition voltage: 150V
  • Anode burning voltage: 140V
  • Anode extinguishing voltage: 120V
  • Max anode voltage: 170V
  • Cathode current min: 1.5mA
  • Cathode current max: 2.5mA

With a suitable power supply unit, I was able to quickly set the necessary supply voltages for the functional test.

You can see here that the tube draws a current of 2.8mA at a burning voltage of just under 140V. This corresponds to an output of 392mW. So if I extrapolate and all six digits of the watch are continuously energized, then the power supply for the tubes must bring about 2.3W.

So the tubes already work. Now I can think about what the clock should look like and even more how I want to design it.

The idea is that a microcontroller should control all six tubes. I want to realize this with 8-bit 4094 shift registers, of which four bits each are used for a tube. These four bits from the shift register should then control the tubes via binary coded decimals (i.e. BCD). However, since the tubes have a connection for each digit, ten separate digit controls must be generated from the four BCD lines. This will be done by a CD4028. The IC CD4028 is a “BCD to Decimal Decoder”. To switch the relatively high voltages of the Nixies, the BCD decimal decoder will drive a suitable transistor. This is where the MPSA42 will do its job. This is an NPN bipolar transistor with a collector-emitter dielectric strength of 300VDC at a maximum collector current of 500mA. In order to be able to use the tubes as flexibly as possible, I have come up with the idea of designing a separate circuit board for each tube. These individual display boards should then be plugged into a main patine. So if a digit is defective, you can simply pull out the board in question and repair it. Then you don’t have to solder around the motherboard.

The microcontroller should find space on the motherboard. The low- and high-voltage supply and the shift registers are also to be accommodated on the mainboard. The display boards only carry the Nixie tube and its driver transistors and the BCD decimal decoder. By means of post connectors, they should be easy to plug into the motherboard. To make these formulations a little easier, I have made this sketch:

Based on this idea, I now began to draw the circuit diagrams. So it started with the display board on which the tube is located. The circuit design is very simple. Two opposite post connectors should give the board a stable hold on the motherboard. One of the connectors supplies the BCD decimal decoder (CD4028N) with the four data inputs and the 5V supply voltage for the logic. On the other side of the board, the “high voltage” is provided for the tube.

From this I could then simply create a layout and then produce it as a prototype as a board.

Nach dem Ätzen und Bestücken der ersten Platine und fünf Weiteren war der erste Schritt der Nixieuhr getan:

In order to test the first part of the work, I had a DEB100 digital experiment board available at my workplace. The following short video shows the test result:

After all six boards were equipped and tested, I had dealt with the planning of the motherboard. At the beginning, of course, there was again the creation of a circuit diagram. From an external 12VDC source, which should ideally be a simple plug-in power supply, the supply voltages had to be generated. On the one hand I needed a 5VDC supply for the microcontroller, the shift registers and the BCD decoders and on the other hand a “high voltage” of 140VDC for the Nixie tubes. The 5V supply was done quickly – here a 7805 linear controller should do its job. Since the power consumption of the digital components is relatively low, no complex measures were required here. The 7V difference on the 7805 at the few milliamperes he packed without great power dissipation heat dissipation. For the generation of the 140V I made a step-up converter with an MC34062 (Inverting Regulator – Buck, Boost, Switching) controller, which switches a 220uH inductor via a FET. Via a voltage divider with trimming potentiometer at the output, a voltage feedback can be sent to the comparator output of the controller and thus the output voltage can be adjusted. As a microcontroller, I always use Atmega328 and the like for most of my projects (due to the stock level :)). This is also the case here. The result is the following circuit diagram:

From this I made a layout again and etched and equipped a board again. However, this prototype test board was only a version with four digits. The reason was also that I did not have a larger raw board available 🙂

From this I made a layout again and etched and equipped a board again. However, this prototype test board was only a version with four digits. The reason was also that I did not have a larger raw board available 🙂

After various successful tests with the prototype board, I ordered professionally manufactured boards from the board manufacturer I trust. After assembling them, I then created a test program that could control all digits. A short test video is linked below:

The following photos show how the clock looks with the “beautifully” manufactured boards. To make the whole work even more nostalgic, I had the idea to mount the boards on a milled wooden panel. (Thanks to Gebhard for the woodwork). In order to keep the watch electronics permanently dust-free, I had a transparent Plexiglas hood made.

Sketch for the arcyl glass hood

As so often, I made the software with the Arduino IDE. To flash the microcontroller I use the AVRISP mkII Programmer. If somebody is interested in the code, I can also post it here on the blog.


Video streaming in the car – Android Auto – the cheap solution


Since my leisure activities are increasingly taking place outdoors in the currently somewhat warmer season, writing the weblogs suffers a little. But I’m still working on some projects, repairs and restorations. In this way, a lot of material comes together again in order to write articles from it – in the colder season of the year. This time I was just annoyed about the rip-offs and pricing in the automotive sector and looked for an alternative solution.

It’s about my five-year-old car, which is equipped with an on-board navigation system. The navigation data is saved on an SD card inserted in the vehicle. So far so good. However, the map data of the vehicle are now getting on in years and much is no longer up-to-date. Something like that is particularly annoying if you are on a vacation trip and the GPS does not know the destination or has not mapped the way there. No problem, I thought to myself, map data is on the SD card – there are sure to be updates. And yes there is – but the map updates cost upwards of 200 euros and more. In return, I get a complete navigation device including the latest maps with free online updates.

So I tried to make myself smart and find a current map on the network and save it on the SD card. But of course that doesn’t work. Some security mechanisms are used here. For example, the hardware ID of the memory card is stored (coded) in the navigation system. So my first attempt to copy the original navigation map as an image on a new SD card failed. It is recognized as an invalid card. And tinkering around with the VCP and VCDS diagnostic device in the navigation computer without instructions is too much effort for me. So another option had to be found. An online navigation system is installed on every smartphone – it’s called Google Maps. And there are also some offline navigation systems that can be downloaded free of charge from the web stores. So my idea was to add a phone mirror function to the car. (These things are called Android Car Play in the fruit department, etc.) Since my old box does not provide any of it in the entertainment system, there were the following alternatives for me:

Either I buy a China Navi to retrofit – and by that I mean the screens that are based on the original on-board monitors of the car, in which an Android computer is then installed. The corresponding apps for navigation and other gadgets can then be installed there. The data of the original image of the car infotainment system are of course still displayed. Such systems are available in the order of 400-600 euros. Then there are a few hours of installation (handicraft) work.

Another option is a retro fit conversion. This means that I install the higher-quality infotainment system with the corresponding range of functions in the vehicle. That in turn means: expanding the old system, buying a new system from the vehicle manufacturer including all necessary control units, cable harnesses, cover panels, etc., then installing it and then coding everything with a lot of effort, importing parameters, etc. The costs are immense and add up no case (> 2500, – if that’s enough) and then the work for the removal and installation. -> everything can be forgotten.

MiraScreen receiver

And here is the last option for all together just 50 euros and with an effort of 30 minutes installation consisting of the following points:



  • Activate the Video In Motion (VIM) function of the display or the radio unit
  • purchase an AMI cable with composite video in and audio in
  • purchase a MiraScreen WLAN receiver for just 40 euros, which is able to output the video signal via CVBS
  • install the entire part (in this case) in the center console shelf
  • Lay the cable for the power supply of the Mirabox through the shelf to the 12V socket and connect it.

This work is done quickly and the smartphone can be connected via “Stream” (in the Android smartphone under “Wireless transmission in Bluetooth & device connection”). Now the screen and the sound of the smartphone are also reproduced via the infotainment system of the vehicle.

AMI videocable

The AMI video cable is plugged into the AMI socket of the vehicle and the analog video and audio lines are connected to the chinch plugs of the MiraScreen connection cable.

Connector for supply, video and audio to the MiraScreen

I took the power supply for the Mira Screen directly from the 12V socket behind the center armrest. To do this, I pinned the plug of the 12V socket, soldered a wire to 12V and GND and pinned it back in. At the other end of the two wires I crimped a 13.5mm Tamiya coupling. In addition, the 12V line has also received air traffic control. The Mira Screen connection cable, which is threaded through the shelf, is now threaded onto this Tamiya coupling and the corresponding Tamiya plug is crimped on. To get the cable through the shelf, I simply drilled a 7mm hole and put a rubber edge protector into the hole.

Cable entry

Once the cable is connected, the box can be plugged in and stowed in the shelf.

In the picture above, the box is fully connected and can be seen in the center armrest shelf.

If the backrest is folded down, nothing can be seen of the box. They can also be removed quickly and easily after unplugging the connector.

Now that the ignition is switched on, you can select “Media” in the multimedia system and then click on CVBS video input. The start screen of the Mira Screen Box should now be visible. The Mira Screen Box can also be configured by connecting the mobile phone via WLAN with the SSID “MIRAxxxx” and entering the IP address that is specified on the start screen in the smartphone’s browser. The SSID password is also on the start screen.

The photos above show the inside of the box. With this device, the pin header of the stack board had partially loosened from the socket strip and this had led to contact problems between the two boards. The brass spacer (can be seen in the last picture at the bottom left) is 2mm too long, so that the two boards do not stick together properly. As a remedy, I shortened the two spacers by these 2mm and screwed them back on. So I can use the Google Maps in the car without any problems.




Selfmade ROM module for Vectrex


For the Vectrex game console a home arcade machine from 1982, there were, or there are a very limited number of game titles available. I will present the Vectrex itself, or the restoration of this darling, in a separate article.

The games were available in the form of ROM modules and had to be inserted into the side of the console. Today, like the console itself, they are pretty rare and difficult to find. In terms of price, they are usually not bargains either. There are also replicas, multiroms and some DIY projects that keep the game program or even several games saved on the basis of the old EPROMS and were thus playable via a “module”. Since I also have all sorts of Eproms with different sizes in the component store and also got a couple of 27C512 Eproms sponsored by a colleague (thank you Jürgen), I just had to try to tinker with a ROM module.

originale Vectrex ROM-Module board

So quickly thought about what I would need for this. Here is a small list:

  • old EPROMS (I use Eproms that can be erased with UV light)
  • an Eprom programmer (in the back corner of a box I found a ChipLab programmer with a parallel interface)
  • an old computer with a parallel interface and an older operating system (Windows XP). Fortunately, I once again did without disposal and brought an old laptop back to life.
  • software for the programmer (here I use “ChipLab” which can run on WindowsXP with the help of “porttalk22”)
  • the binary data or HEX files of the original ROM modules (you can use the internet search for this)
  • a layout tool (Autodesk Eagle)
  • a craft shop where you can etch circuit boards, or an account with
  • a Far Eastern PCB manufacturer
  • Soldering tools and small parts
  • and of course a Vectrex – otherwise none of this makes any sense

In order to determine the memory requirements of the Eproms, I first have to know the size of the games. Here is the list of titles and their size:

Games with a size of 4 kB (4 kilo bytes). This corresponds to an address range from hex 0000 to 0FFF

  • Armor Attack
  • Art Master
  • Bedlam
  • Berzerk
  • Clean-Sweep
  • Cosmic Chasm
  • Engine Analyzer
  • Hyperchase
  • Minestorm 2
  • Rip Off
  • Scramble
  • Solar Quest
  • Space Wars
  • Star Castle
  • Star Hawk
  • Star Trek

Games with a size of 8 kB (8 kilo bytes). This corresponds to an address range from hex 0000 to 1FFF

  • Animaction
  • Blitz
  • Fortess of Narzod
  • Heads Up
  • Melody Master
  • Pitchers Duel
  • Pole Position
  • Spike
  • Spinball
  • Tour de France
  • Web Wars

Games with a size of 12 kB (12 kilo bytes). This corresponds to an address range from hex 0000 to 2FFF

  • Dark Tower

Next, I’ll take a look at the Eproms for pinout and size. I have two sizes available for the number of pins. Eproms with 28pin and 32pin in DIL housing. The following types belong to those in the 28-pin housing:

  • 27c64         8k x 8 bit  so   64 kb (kilo Bit)
  • 27c128   16k x 8 bit  so 128 kb (kilo Bit)
  • 27c256   32k x 8 bit  so  256 kb (kilo Bit)
  • 27c512   64k x 8 bit  so  512 kb (kilo Bit)
picture from (
picture from (


The pinout is identical except for the different number of address lines. However, the 1Mbit variant 27C1001 (27C010) has a different pinout.

Bild von (

The next step is to look at the pinout of the Vectrex module bay. The pin numbers of the module are marked in the picture below.

Pin Nummerierung des Vectrex Moduls

The signals associated with the pin numbers can be found in the Vectrex circuit diagram of the mainboard. The picture below shows an extract from the circuit diagram with the area of ​​the 36-pin cartridge connector. (Source:

All the information you need to start with a circuit diagram and layout has now been collected. I looked for an eagle layout for the circuit board connector on the web. But nothing could be found straight away. So an original ROM module had to be used as a reference for the dimensions and spacing of the contact pads. With the dimensions removed in this way, it was quickly done and I had drawn a new Eagle component and saved it in the library.


I drew two variants of the module circuits. One for the EPROMs with 28 pins and one for the 1Mbit ROMs with 32 connection pins. (Since there is also space for more games here) In order to be able to distribute all possible sizes of games differently on the EPROM, I have made address bits 12, 13 and 14 switchable. In such a way that these three address lines can either be controlled by the Vectrex or selected externally by the operator using DIP switches (L / H). Bits 15 and 16 (can also be selected via DIP switches).

The following table shows a few examples of how the start addresses of the games can be selected.

game adresses
start – end (hex)
L L L L L at 8k game 0000 – 1FFF
L L L H L at 8k game 2000 – 3FFF
L L H L L at 8k game 4000 – 5FFF
L L H H L at 8k game 6000 – 7FFF
L H L L L at 8k game 8000 – 9FFF
L H L H L at 8k game A000 – BFFF
L H H L L at 8k game C000 – DFFF
L H H H L at 8k game E000 – FFFF
H L L L L at 4k game 10000-10FFF
and so on…
Ansicht im Hex Editor

Provided, of course, that the game data was written to the EPROM in this way. To do this, I use one of the many freeware hex editors (HxD) and assemble a binary file from the individual game images. This “file” is then imported into the ChipLab software, the correct EPROM is selected from the database, then the chip is inserted into the programmer and off you go … (First, check again whether the chip is empty. Otherwise it has to ” topless “in the sun, or under the UV lamp (for about 15-20min)

Eprom inserted to the programmer

Once the chip has been filled with bits and a layout has been made from the circuit diagram, a prototype can be etched. To do this, I was able to use our company’s etching system in a short lunch break and remove the unnecessary copper from the board using etching technology.

pcb layout printed on foil

After exposing a double-sided board coated with photopositive lacquer and then developing it, the excess copper can be removed with EisenDreiChlorid. What remains is the desired structure.

Sometimes a selfie in between. It takes about 57 seconds to expose the circuit board to UV light. Enough time to take stupid photos with the phone: D


The next step is to drill the holes in the board. The vias (VIAs) from the top to the bottom layer are not implemented in the prototype by galvanic application of copper in the holes, but by hand by pushing a piece of silver wire through the hole and then soldering it on both sides.

the etching is completed

Now all that’s missing is the assembly. But it is done very quickly. Because apart from the IC socket, a couple of pull-up resistors and the DIP switches, there isn’t much on the board. So solder the few parts, put the chip in the socket – and the ROM module is ready.

ready assembled ROM module

What the finished module looks like on the Vectrex and, above all, how it works, I’ll show you in a short video. I also embellished the board a bit and commissioned it as an industrially manufactured circuit board from a Far Eastern printed circuit board manufacturer …

(small update on October 20, 2020)
The circuit boards made in far east have come and, in my opinion, look quite acceptable. A board is quickly assembled … here is the result:


The Wetterfrosch 2.0 or environmental data logger


A few years ago I presented a project in which a Raspberry Pi was working as a data logger. A few sensors were connected to this Raspberry, which recorded environmental data such as air temperature, relative humidity, air pressure and the current GPS position. The sensors mostly consisted of ready-made breakout boards that were connected to the RaspberryPi via the various buses (I²C, Serial, SPI …). Python scripts ran on the PI itself, which read out the sensors, summarized the data and stored it on a USB flash memory. I then built this hodgepodge of components into a plastic box with a size of 150x80x50mm.

But it’s also about a lot smaller. As part of a small project, the task was to downsize this sensor / data logger. My approach to realizing this was very simple: “Everything new”. So I changed the concept like this:

  • the RaspberryPi is replaced by a microcontroller
  • a circuit board is created on which all components are housed
  • the recorded data is saved on a microSD card
  • the board is reduced to the most essential components. The sensor electronics and the SD card reader are placed directly on the board
  • a GPS receiver (in the form of a breakout board) should be able to be plugged in as an option
  • the controller is programmed via an ISP interface
  • the power supply is 5V DC

From this I created the following block diagram:

Block diagram

As is so often the case, the central element is the Atmega328 microcontroller. As an external circuit, it only needs a quartz for clock stabilization. (More precisely, it also offers the option of using internal oscillators …) The microcontroller communicates with the sensors HYT939 and BME280 via the I²C bus. The level from 5V on the controller side to 3.3V on the sensor side is adjusted via the sophisticated bidirectional level shifter circuit using a BSS138 Mosfet with an integrated body diode. This circuit is used for both the SCL (Serial Clock) and the SDA (Serial Data) line.

The data is saved on a microSD card. A card slot is installed for this, which communicates with the controller via SPI (Serial Peripheral Interface). An adjustment of the signal amplitudes is also necessary here. This time, however, the TXB0108 chip from Texas Instruments takes care of that. This is an 8-bit bidirectional level shifter.

A button will start and stop data recording and a LED will display various status messages through flashing sequences.

The optional plug-in GPS module works with a 5V power supply and the levels of the serial data communication (RS232) are also 5V compatible.

Last but not least, the power supply must of course also be planned. Only an external, stabilized 5VDC source should be connected here to supply the logger. The 3.3VDC required for the sensors and SD card are generated on the board by means of an LDO (Low Drop Out) controller.

Once all components and their interaction have been defined, the circuit diagram is drawn from them. For my handicraft projects I mainly use the schematic and layout editor “eagle”. The circuit shown below results from the block diagram.

From the circuit diagram I created a layout with two layers, the floor plan of which has the dimensions 55x25mm. Except for the connectors, only SMD components are on the board.

In the layout tool there is the function to view an optical preview of the finished board. In this way you can check in advance whether the board corresponds to the requirements and, if necessary, optimize the position of the components. Once this is done, a package with production files (Gerber files) is generated from the design and this is then sent to the circuit board manufacturer you trust. Since it is also located very, very far away, production also takes a few days. But in the end the circuit boards arrive and are also impressive. 🙂

The two pictures above show the board from the TOP and the BOTTOM side. The next step is to order the components according to the plan and then assemble them.

I do the assembly by hand with a soldering iron suitable for the SMD components with a correspondingly small tip. For the very small parts, such as the BME280 sensor, a microscope or microscope camera is also used.

The two pictures above show what the board looks like after it has been assembled. The following photo shows the size difference of the finished logger with the attached GPS module compared to the old “weather frog”After completing the hardware, it is now time to start with the software. I tinkered it in a practical way with the Arduino IDE tool and flashed it to the controller via AVRISP mk2 via ISP. In order to get the AVRISP to work on a Windows 10 computer, a suitable driver must be installed. (libusb-win32- helps here)

program code created with the ArduinoIDE
controller flashed with AVRISPmkII

Data recording is started on the SD card after applying the supply voltage and pressing the button. The measured values ​​are written every second. If, as in this example, the GPS sensor is plugged in, the GPS data is also recorded. The software also records if the GPS sensor does not have a “fix” yet. (Since there was no GPS fix in the example log below, no valid GPS data is included.)

Example of the data log:



Configurable plug-in power supplies


This short post is only intended as an aid to be able to look up quickly if necessary. Over time, each of us will probably accumulate countless power packs and adapters. Some are fixed voltage power supplies, others can be adjusted in the range of the output voltages. The output voltages of these power supplies can be adjusted with slide or rotary switches or with small plugs (jumpers) in which resistors are built-in.

The voltage that is set is always printed on the jumpers. There is a small catch, however. If you have several different power supplies (different in terms of performance and output voltage range), you quickly have a hodgepodge of different resistor jumpers. The problem now is that the jumpers all look the same and are also printed with the same voltage values. If you don’t sort them properly according to the respective power supply units, the mishap happens quickly. An example: A type SPS24-24W power supply unit has a jumper labeled 9V. The jumper has a resistance of approx. 9kOhm. Another power supply of the type SPS12-23W also has a jumper marked 9V – but a resistance of only 1.5kOhm. And so it quickly happened that you (or I) plugged in the jumper from the wrong power supply. In my example I put the 9V jumper with 1.5kOhm into the SPS24-24W power supply. Before I was with the test leads at the cable socket, there was a thud, a well-known cloud of smoke and the associated smell of a burst capacitor (electrolytic capacitor).

What happened? The value of the wrong jumper resistance was smaller than the smallest value of the correct jumper (24V = 2.42kOhm). So the output voltage was significantly higher than 24V and thus also significantly higher than the dielectric strength of the electrolytic capacitor at the output (which had a dielectric strength of 25V at 220µF).

To avoid this in the future, I measured the resistance values ​​to match the power supply models of the SPS series.

Model SPS12-12W-A (unfortunately I don’t have a copy of this model – if someone has one at hand, I would be happy to include the resistance values ​​in the list here)

3V ………….  0.00k
4.5V………..  0.00k
5V…………… 0.00k
6V…………..  0.00k
7.5V……….  0.00k
9V …………  0.00k
12V………..  0.00k

Model SPS12-24W-B
3V …………. 373.0k
4.5V………..  6.01k
5V…………… 4.51k
6V…………..  3.08k
7.5V……….  2.04k
9V …………  1.54k
12V………..  1.02k

Model SPS24-24W-A
9V ………….  9.09k
12V…………  5.75k
13.5V……..  4.97k
15V…………  4.29k
18V…………  3.39k
20V ………..  2.98k
24V………..   2.42k

Model SPS24-48W-B
9V ………….  17.38k
12V…………  8.27k
13.5V……..  6.78k
15V…………  5.48k
18V…………  4.20k
20V ………..  3.60k
24V………..   2.78k

edit 10.52021: Added pictures of the board of the power supply SPS24-24W-A:

CO2 measurement with SCD30, Arduino and Matlab


This project – actually a mini project – might also be interesting for one or the other. It is the now well-known and frequently used carbon dioxide sensor SCD30 (CO2 sensor) from the manufacturer Sensirion. There are a number of projects that can be found on the internet. As part of a quick test setup, I tried to read out the data from the sensor using an Arduino Uno board in order to then display it in a plot using the Matlab software. The data transfer takes place via the serial interface or via the serial protocol of the USB-UART.

To connect the SCD30 to the Arduino, you need the power supply and the I²C data bus – so in total just four wires. This means that the minimum configuration is fulfilled and the data can be read out.

The sensor itself works on the principle of NDIR technology. (NDIR = non-dispersive-infrared). That means the sensor is a small spectrometer. The medium to be examined is fed into a sample chamber. The sample chamber is illuminated by an infrared source and the IR light shines through the medium and a very narrow-band wavelength filter and then hits the IR detector. The wavelength of the filter is designed in such a way that precisely those wavelengths are let through that are absorbed by the molecules of the medium (gas). Depending on the number of molecules or the density of the gas, fewer light beams are recognized by the detector. A second measuring chamber, which is filled with a reference gas, serves as a reference. A controller on the sensor evaluates this information and forwards it in the form of ppm via the I²C (or switchable MOD-Bus) interface. There is also a temperature and humidity sensor on the board, the data of which can also be read out via the bus. The preset I²C address of the SCD30 is 0x61. The exact information on the data protocol can be found in the documentation from Sensirion.

Ideally, as almost always, there is already a ready-made library suitable for students for the various microcontrollers. So you don’t have to worry anymore and can read out the data from the connected sensor directly. The example programs can be found under the examples of the libraries.

electrical specifications

The Arduino with 3.3V or 5V can be used for the supply voltage of the sensor. However, caution is advised when using the I²C bus: Here the input high level is set at 1.75-3.0V and the output high level with a maximum of 2.4V. But on an Arduino the levels are 5V !! So a level shifter has to be built in here – or at least, suitable resistors for a quick test.

The program code listed here essentially comes from the example of the library by Nathan Seidle from SparkFun Electronics:

By: Nathan Seidle SparkFun Electronics  
Library: http://librarymanager/All#SparkFun_SCD30  

#include <Wire.h>
#include "SparkFun_SCD30_Arduino_Library.h" 
SCD30 airSensor;

void setup()  
  //Serial.println("SCD30 Example");
  airSensor.begin(); //This will cause readings to occur every two seconds

void loop()  
  if (airSensor.dataAvailable())
   // Serial.print("co2(ppm):");

    //Serial.print(" temp(C):");
    Serial.print(airSensor.getTemperature(), 1);

   // Serial.print(" humidity(%):");
    Serial.print(airSensor.getHumidity(), 1);

    //Serial.println("No data");



With these lines of code in the Arduino Uno and the correct wiring (SDA -> to Arduino A4 and SCL -> to Arduino A5 via a suitable level converter) you can continue with Matlab. The Arduino should now output the following lines in a serial terminal: (example)

463,28.5,12.4 … und so weiter

This now has to be read into Matlab and recorded over a definable period and at the same time displayed in a plot. The matlab script here makes it possible … (pn if someone needs it)

The result is a plot that shows the course of CO2 in the room (in this case on my office desk).



Small craft project for the summer time


solar module

As a mini – craft project for the summertime I call the following tinkering. A small monocrystalline solar module called “SM 6” from a well-known large electronics distributor starting with “C” and ending with “d” plays the main role in the project. The module has a nominal power of 6Wp with a maximum current of 320mA. The rated voltage is 17.3V. The open circuit voltage is 20.8V. The silicon cells are embedded in an EVA (ethylene vinyl acetate) plastic sheet and are UV and moisture resistant. The whole module is about 25cm x 25cm in size. It is thus ideally suited to provide the power to power USB devices. For example, I thought about WIFI IP cams. It should also be possible to charge smartphones or tablets.

In order to be able to do this, the operating voltage of the USB standard (5V) must be generated from the rated voltage of the photovoltaic cell. You could do that easily with a 7805 controller and convert the difference into heat. But this is the least efficient way to get the panel’s energy into a cell phone. Firstly, the internal resistance of the panel depends on the light intensity, which has a major impact on the efficiency of unmatched load resistors. On the other hand, a series regulator is a power shredder, since the difference between input voltage and regulated output voltage is converted into power loss, ie heat, during the flow of current. Here you are better served with a switching converter (buck converter).


In a simple laboratory setup, the behavior of the panel can be examined. For this purpose, the open circuit voltage of the panel is measured at different illuminance levels. Subsequently, the panel is loaded with different resistance values ​​and the current through the load as well as the voltage at the panel are measured. The measured values ​​are recorded and the Ri (internal resistance of the source) is calculated. The following circuit diagram shows the measurement setup:
measurement setup – schematic
The ammeter is an Agilent and Voltmeter Keithley 2701 table multimeter. These gauges can both be controlled via SCPI commands. The interface is a LAN port. This makes it easy to implement an automated measurement process via a PC and a suitable script. And since Matlab offers a very convenient way to script, it’s also used right now. In order to be able to measure in a laboratory and have approximately the same environmental conditions, a table lamp with halogen bulb is used instead of the sun. The brightness of the lamp is easily adjusted by supplying it with a laboratory power supply of 0-13V. Of course, the laboratory power supply can also be controlled by Matlab.
measurement setup with lamp as “sun”

The lamp is placed at a distance of 25cm in the middle of the panel. In order to get a feeling of which illuminance is achieved with the lamp, a reference measurement is taken with a luxmeter. That is, the lamp goes through the power ramp of 0-13V and the lux meter measures the illuminance at a distance of 25cm under the lamp. The whole thing is resolved in 0.5V steps. This results in a curve that looks like this:

Voltage on the lamp results in illuminance

Now the measurement can begin. Resistors are manually connected to the panel as a load resistor and current and voltage are measured at each brightness level. There are eleven load resistance values ​​ranging from 4.7 ohms to 220 ohms connected in sequence. An idle measurement is then of course made without load resistance. The following graph shows the calculated internal resistance for two loads of the panel over the brightness curve of the lamp in lux and in the other graph over the voltage at the lamp (for better scaling). The internal resistance of a source is calculated from the open circuit voltage of the source minus the voltage under load, divided by the current. With the difference between the no-load and load voltage, the voltage drop at the internal resistance is obtained. Since the load is also known as the current, it is only necessary to use Ohm’s law to obtain the resistance value …

Internal resistance vs. illuminance

Internal resistance vs. Voltage on the lamp

Since some clarifications about the behavior of the PV cell have now been eliminated, I can briefly report on the structure of the voltage converter. As previously announced, a switching converter is the more efficient way to adapt the energy to the consumer. Here comes an LM2596S used. The LM 2596 is a “Simple Switcher Power Converter” that switches at 150kHz and can supply a load with 3A.) Here is an overview of the functions:

  • 3.3-V, 5-V, 12-V, and Adjustable Output Versions
  • Adjustable Version Output Voltage Range: 1.2-V to 37-V ± 4% Maximum
    Over Line and Load Conditions
  • Available in TO-220 and TO-263 Packages
  • 3-A Output Load Current
  • Input Voltage Range Up to 40 V
  • Excellent Line and Load Regulation Specifications
  • 150-kHz Fixed-Frequency Internal Oscillator
  • TTL Shutdown Capability
  • Low Power Standby Mode, IQ, Typically 80μA
  • Uses Readily Available Standard Inductors
  • Thermal Shutdown and Current-Limit Protection

(source: datasheet from vendor TEXAS Instrument)

With this switching converter and a few other components can quickly assemble a circuit and transform with the layout tool “Eagle” into a board. However, this circuit is so simple that it only works as efficiently as possible with the advantages of the LM2596, but does not perform any power tracking. This means that the load representing the circuit for the solar cell is not adapted to the internal resistance of the solar cell.


Circuit diagram of the DC-DC converter

From this circuit, a simple layout was created, a board etched and equipped. A USB socket on the output allows the direct connection of USB devices. To make the whole thing look a bit reasonable, I have donated the board still a small plastic casing …

measurement setup
Switchable load resistors
Layout on the computer
Foil for creating the printed circuit board
Etched PCB
Etched PCB
Finished circuit

Circuit diagram of the DC-DC converter

A simple layout was then created from this circuit, a circuit board was etched and assembled. A USB socket at the output enables direct connection of USB devices. To make the whole thing look a little sensible, I donated a small plastic housing to the circuit board …

Measurement setup
Switchable load resistors
Layout on the computer
Foil for creating the printed circuit board
Etched PCB
Assembled PCB
Finished circuit