Here you’ll find a few direct links to important content of this page:

Electronic projects:

Most pins are in use

Most pins are in use

The ESP8266 is an interesting chip, I mentioned it here several times (sorry: mostly german). In a short description, it’s a freely programmable microcontroller. Compared to Arduino & Co., it’s a real number cruncher. The ESP is faster, has more memory, and the best thing: it has builtin WiFi. You’ll find more information all over the network, a basic overview is contained in Wikipedia.

I tested several boards when playing with this chip. Today, I want to describe one that goes with the name Witty Cloud.

Basically, it’s a board with an ESP-12-F, a USB connector that delivers power, a little pushbutton, a LDR (Photoresistor) and a RGB-LED. So there’s plenty of hardware to play with. When you buy the module, you receive a stack of two PCBs. The lower one has a second USB connector, which is equipped with a serial converter. So it’s not only used as a power source, but also as a programming and debugging interface. Furthermore, there’s a reset- and a flash-button on the lower board. After programming, you just need the upper board, and you can even send newer firmware versions to it over the air (OTA).

The  lower board is only used for programming

The lower board is only used for programming

Stacked like this, the module costs less than three Euro, you just need a USB cord and a compiler to start programming. I suggest using the Arduino IDE, it’s very easy to use, even for beginners. After installation of the ESP8266 extensions, it’s best to select WeMos D1-Mini in the board manager, this way everything works fine.

Unfortunately, it’s not easy to find proper documentation for the Witty. So i scribbled the picture above, at first to have some kind of reminder for myself. So the pin labeled GPIO13 is connected to the blue channel of the RGB-LED, in the Arduino environment it’s called D7.

Label Pin (Arduino) Purpose
REST Reset
ADC A0 Analog input, connected to LDR
CH_PD Chip Power-Down
GPIO16 D0 GPIO, freely usable
GPIO14 D5 GPIO, freely usable
GPIO12 D6 GPIO, green channel of RGB-LED
GPIO13 D7 GPIO, blue channel of RGB-LED
VCC +5V power
TXD TX Serial interface
RXD RX Serial interface
GPIO5 D1 GPIO, freely usable
GPIO4 D2 GPIO, connected to pushbutton
GPIO0 D3 GPIO, connected to flash-button, not really freely usable
GPIO2 D4 GPIO, connected to blue LED on the ESP-Module
GPIO15 D8 GPIO, red channel of RGB-LED
GND Ground

I would be highly interested in a circuit of the board, and if you have any corrections or suggestions: just let me know.

Mein Fazit: ein echt interessantes Board. Wer mehr GPIO braucht sucht vielleicht lieber nach einem NodeMCU, wer sowieso einen LDR oder eine RGB-LED braucht sollte zugreifen. Ich habe mittlerweile einige davon hier, und eine Firmware mit der ich die Dinger hier im Haus verteilen möchte ist auch fast fertig.

Oh, das Bild habe ich übrigens mit einer Grafik aus diesem Projekt gemacht, das ist die Witty Cloud für Fritzing.

The completed controller

The completed controller

This is a project from 2004. I had it covered extensively on my old homepage, including some more pictures, circuit diagrams and a description on how I analyzed the keyboard controller.

Nowadays, PCs don’t have a PS/2-interface anymore. I’d base a project like this on microcontrollers if I would do it again, and interface the computer via USB. So I leave the details in the past and give just a short description of the project.

At that time, I was interested in MAME, the Multi Arcade Machine Emulator. You can play all the old arcade game classics with that. A PC keyboard is not the ideal interface for thos games, so I started building my own controllers.

Ratsnest

Ratsnest

Originally, the joysticks were sold to fit a Sega Dreamcast console. I threw out the electronics and implanted a PC keyboard controller instead. I had to find out the keyboard matrix layout and interface all the joysticks microswitches to the right contacts on the controller board. Not too complicated.

The second player’s contacts were connected to a second unit with an old serial cable. Additionally, I built a Y-adapter for the PS/2-interface, so I was able to control the PC outside of MAME.

The result surely wasn’t a pretty build, but: it worked. :-D

Nowadays, I don’t have a PC with a PS/2-interface anymore. I already dismantled one of the joysticks and built something else. But that’s a different story…

See also…

What's wrong with this?

What’s wrong with this?

This is another old project, dating back to about 2004. I had it covered on the old Schatenseite, and I want to give a short presentation on the blog to preserve it.

I was given an old Commodore C64 that somebody decided to dispose of. The first version, in germany this case is dubbed ‘Brotkiste’ (bread box). It didn’t turn on anymore, and lacking any personal Commodore history I didn’t hesitate long before taking it apart.

Unfortunately, I didn’t know about microcontrollers at that time, otherwise I would have been able to save the functionality of the keyboard. I wasn’t able to, so parts of the underside of the keyboard had to go, to make space for CPU cooler and RAM. :-(

I inserted a VIA EPIA M10000b, so the C64 ran at 1GHz. The system was completed by 256MB RAM, a 2,5″-20GB-harddisk, a CD-ROM from a notebook and an external power brick.

The C64-PC

The C64-PC

Built like this I could attach the unit to my TV set, mainly for playing some games on it. But to be honest: this was one of the projects that made more fun during the build than afterwards…

Nowadays I would build this in a different way. A Raspberry would look great in the case. Needing much less space it would even be possible to keep the keyboard in a working condition. And running the Retropie distribution you could even have this certain 80’s feeling… :-D

See also…

I mentioned this project in an article (german only) on this blog, it dates back from November 2012. Somehow I never showed it, I don’t really know why.

Those who read this blog for a while know that I have a deep faible for computer keyboards. You don’t get the full picture from my english language articles, but in german you can find many keyboard related articles on this site.

Amongst others, my collection contains two vintage Apple keyboards. There’s a — really not too shabby — Apple Extended Keyboard II, which was built between 1990 and 1994. Many enthusiasts claim that this is the best keyboard ever produced by Apple, partly of course because of it’s mechanical nature with the Alps switches.

Even more original — and in my eyes it’s a typical Apple product — is the Apple Adjustable Keyboard, 1993 vintage. Typical Apple? As I said, in my eyes: it was expensive for its time, and above all the visual appearance of the product is more important than functionality. Even though there are arrow-keys on the main keyboard, I personally wouldn’t want to miss function- and navigation-keys (Home, End, PgUp, PgDown). And if you connect the additional keypad, you really have to have long arms to reach your mouse… :-/

However, I wanted to give both a try. And since I don’t have access to a computer with ADB interface — Apple killed it in 1999 — I needed a converter. You can buy this stuff, but you don’t have to.

On geekhack.org, there’s a japanese developer called hasu, who is tmk on Github. He created and published the TMK Keyboard Firmware Collection. That’s a firmware that can be run on several AVR-based platforms, notably the Teensy 2.0 which is well known in keyboard communities. The firmware is able to ‘talk’ several different keyboard protocols. Of course, USB in one direction, to be connected to any modern computer. In the other direction there are protocols like PS/2, Sun or Apple Desktop Bus. The custom firmware is loaded with features even expensive modern high end boards fail to deliver. It’s possible to program macros, use media keys or control the mouse pointer with the keyboard.

Unfortunately, I didn’t have a Teensy at home. But I had all the parts to build something compatible, and all the tools to etch a fitting PCB. So I fired up KiCad and designed a minimal circuit, from that it wasn’t too difficult to create a PCB layout:

(The KiCad files need a bit of a workover, so I won’t publish them here. But it should be easy to recreate the circuit following the two screenshots.)

ADB USB Converter

ADB USB Converter

The finished converter measures in at 2x5cm, that’s really tiny. But the important thing is: it works!

I could probably use the ADB mouse with an off-the-shelf converter. But honestly: even a hardcore fanboy would prefer a modern pointing device without the ball in it. That is: a while ago I had the opportunity to play a bit with System 7.5 (the Apple operating system from the same era as the two keyboards), and I have to confess that the Adjustable Keyboard did its part for the authentic user experience… :-D

In Star Trek TNG, Captain Picard is shown as the epitomy of wisdom. I just recognized that yesterday, watching the episode Devil’s Due:

Data, from your own experience of performing Ebenezer Scrooge, you’re aware how fear can be a very powerful motivator. […] And in the hands of a con artist, fear can be used to motivate obedience, capitulation, the exploitation of innocent people. And that is what I believe has happened here.

The episode is from 1991, and everybody can decide for themselves if this quote fits into our current reality. For me, TNG always has been the best part of the Star Trek franchise.

A look back

A look back

Just until a few hours ago, the Schatenseite — my main homepage — was running with the Typo3 content management system. I installed it about twelve years ago, and I’m still certain that people can build awesome sites with it. However, Typo3 maintenance takes more engagement than I’m willing to invest. And Typo3 as a CMS was too big for my little page, anyway — which was clear from the start… :-D

I’m running my blog since 2004, and I think most of my content fits better into a blog than into a classic ‘homepage’ format. So old projects are ‘fading out’, instead of me taking them offline. So I moved my blog to the main page. I preserved parts of my old homepage by ordering some articles into the blog. I kept chronoligical order with this, so what I wrote in 2006 will be found in 2006, even if I copied the content in 2015. I put a sticky article onto the front page, so it’s easy to find the main project pages.

Ages ago, I heard a very wise sentence. Unfortunately, I don’t remember who said that:

Important URLs never change.

I tried to honor that with my relaunch. So on one hand, the most important pages of the old Typo3-site should lead to the right articles in this blog. And on the other hand all old blog URLs should lead to the new location, too. So most links and feeds should continue working properly. People with links to my page, especially those who subscribed the feed, should check if they know about the new locations. For the time being, I’ll keep the rewrite rules intact. But who knows what’s coming…

There’s one more thing I introduced to the blog: parts of the old homepage were already translated into — my very broken — english. I want to expand the english part in the future, so from now on this is a bilingual blog. However, not for the whole content. I like how WordPress keeps the page with the Polylang plugin. I don’t have to translate every single article. But rest assured: the main parts will be available in english, too.

I’d really like to hear what you think about the relaunch. Especially of course, if there still are errors to fix. Does the page look OK? Do the feeds still work for you…?

I took this article from my old CMS in 2015, it wasn’t in the blog until then.

Breadboard in action

Breadboard in action

I haven’t done many microcontroller-projects till now, but more than one of the few projects I did involved controlling LEDs by pulse width modulation (PWM). Doing this for one or more LEDs is a stressful task for a little microcontroller, but if you want to do some other more or less complicated things while keeping LEDs at certain brightnesses is likely to ruin the timings that are used in the PWM. Not to talk about the program code, which gets more and more unreadable if you try to do several different things ‘at the same time’.

For my next project I need to fade some LEDs again, so I was looking for an easier way to do it. The plans include reading from memory cards, talking to real time clocks and displaying text on an LCD, so I’m almost sure that I won’t be able to reliably control the five channels I’m going to use.

The first plan was to use a ready-made chip. I looked around and the best thing I could find was one made by Philips (PCA something, I forgot the number) that can be controlled via I2C-bus. That part is able to control eight LEDs, but apart from ‘on’ and ‘off’ you can set the LEDs only to two different brightnesses. Those are variable, nevertheless, but it would be impossible to light one LED at 20%, one at 50% and one at 80%. Another drawback is that it is SMD-only, and my soldering-skills don’t including working with stuff that small.

So the Idea was to set up a separate controller for LED-fading, that can be externally controlled, ideally via I2C-bus since I intend to use several other devices in my next project that can make use of the bus. So I set up an ATtiny2313 on my breadboard, clocked it with an external 20MHz-crystal and we tried to control as many LEDs as possible…

Pulse width modulation

Controlling the brightness of LEDs by PWM is a common technique, I used it myself in several projects.

The old way

Till now I used to switch on all LEDs that should light up at a level greater than zero, waited till the first of the LEDs has to be switched off, switched it off, waited for the next one and so on. After a certain time all LEDs are switched off, and I start again.

I try to visualize that with a little picture:

In this example, a full cycle of the PWM would need 50 units of time. The first LED is switched on the full time (100%), the second for 40 of the 50 units (80%), the third one for ten (20%) and the fifth one for 30 units (60%). The fourth LED is off (0%). We see that after 50 units of time the modulation starts again.

The drawback of this technique is, that it’s slow. And for each additional channel you try to control, it gets even slower. We tried, but we weren’t able to control more than five LEDs in this way without them to start flickering to a visible amount.

We tried to create an array with all states of the process, so the PWM only would have to loop through the array and set the outputs accordingly. But that didn’t work either, because the used microcontroller doesn’t have enough RAM to store the array.

Thomas’ idea

After some tests that didn’t work out too well, Thomas had a great idea how to implement the PWM. It also works with an array for all states, but the states of the modulation are not displayed for the same time. The first state is displayed for one time-unit, the second one for two time-units, the third one for four and so on. In this way the LEDs are turned on and off more than once per cycle of the PWM, but that doesn’t hurt.

Let’s try to paint a picture again:

So here we see a PWM with eight channels that are able to display up to 64 different brightnesses. Channel one is switched on for one unit of time, channel two for two units and so on. The most interesting thing is on channel five: the LED is switched on for one unit of time, switched off, and switched on again for four units of time.

Lets try a more complicated example — with brighter LEDs, too:

The channels 1 to 8 have the brightnesses 33, 18, 23, 32, 21, 63, 64 and 24.

Brightness 75 on the oscilloscope

Brightness 75 on the oscilloscope

The advantage of this technique is that on the one hand you have to save a limited number of states (six states in the example), and the looping through the states is very simple: state n is sent to the output pins, then we wait for 2^(n-1) time units, then the next state is sent.

Each state represents the bit-pattern that has to be sent during one step. In other words: one column out of the above picture at the start of a new time period. So in this example, we have six states: 01010101, 01100110, 01110100, 11100000, 11110110 and 01101001. The first one is displayed for one unit of time, the second one for two units, the third one for four units and so on…

Using this technique has the advantage that adding more channels does almost nothing in terms of system load. The only time that the algorithm has to do actual calculations is when a new value has been delivered and has to be converted into the states. So using this algorithm, it is possible to show different brightnesses on all free pins of the controller. With an ATtiny2313 that means that you can fade 13 different LEDs while still talking I2C to communicate with other devices!

I2C communication

Speaking I2C is no rocket science, but since one has to do a lot of bit-shifting when implementing it, I took a ready-made library.

The one I used is written by Donald R. Blake, he was so kind to put it under GPL and post it to avrfreaks.net. You can find the original post in a thread called ‘8 bit communication between AVR using TWI‘, and some additions in the thread ‘I2C Slave on an ATtiny45‘.

Thanks for the great work, Donald! And for putting it under a free license.

Since his package seems to be only available as a forum-attachment, and I’m not sure for how long that will be, I included it into the tarball of this project.

Usage

You should be able to use this device in the same way you would use any other I2C-slave:

Connecting it

The controller needs to have the following pins connected in the circuit:

  • Pin 1 – Reset – should be connected to VCC with a 10k-resistor
  • Pin 4 and 5 – XTAL1 and XTAL2 – connected to a 20MHz-crystal, using 22p-capacitors against GND
  • Pin 10 – GND – Ground
  • Pin 17 – SDA – I2C-data
  • Pin 19 – SCL – I2C-clock
  • Pin 20 – VCC – 5V

Your I2C-data and -clock lines should be terminated by 4,7k-resistors to pull up the lines. All the other pins can be used to connect LEDs. They are arranged in this way:

  • Pin 2 – PD0 – Channel 0
  • Pin 3 – PD1 – Channel 1
  • Pin 6 – PD2 – Channel 2
  • Pin 7 – PD3 – Channel 3
  • Pin 8 – PD4 – Channel 4
  • Pin 9 – PD5 – Channel 5
  • Pin 11 – PD6 – Channel 6
  • Pin 12 – PB0 – Channel 7
  • Pin 13 – PB1 – Channel 8
  • Pin 14 – PB2 – Channel 9
  • Pin 15 – PB3 – Channel 10
  • Pin 16 – PB4 – Channel 11
  • Pin 18 – PB6 – Channel 12
Talking to it

For my tests I used an ATmega8 as I2C-master with the library written by Peter Fleury. You can find it on http://jump.to/fleury. Thanks to him for putting it online!

The typical send function looks like this:

Examples

I2C-Fader on testboard

Here, you see all LEDs fading at different speeds.


The code running on the I2C-master to generate this pattern looked like this:

Visible PWM

Here you see the signal of one LED fading from 0 to 127. Unfortunately, my oldtimer-oscilloscope doesn’t trigger correctly in the middle part.


This is the code that ran on the I2C-master:

Drawbacks

Till now, the device worked in all situations I tested it in. So far everything is fine.

I guess that, compared to the ready-made off-the-hook-parts that controls LEDs via I2C, this module is a bit slow. I can’t see any flickering in the LEDs since they are still switched very fast (about every 6ms, which would result in a 166Hz flickering — too fast for me).

Thanks!

Once again, special credits go to Thomas Stegemann. He had the great idea for the PWM-algorithm, and I am always astonished by the patience he has to show me how to do anything complicated in a sick language like C…

About the license

My work is licensed under the GNU General Public License (GPL). A copy of the GPL is included in License.txt.

Download

To prevent misunderstandings: this says that it's not a mediaeval toilet.

To prevent misunderstandings: this says that it’s not a mediaeval toilet.

This article wasn’t on the blog in 2011. I took it from my old CMS in 2015.

I built this photo booth for our wedding in summer 2010.

I can’t remember where I got the idea, I guess I saw something similar somewhere on the net. After everything else for the ceremony was set I had some time to spend. And this idea…

Hardware

Manual

Manual

I had most of the needed material at home. Enough wood, a cloth for the curtain, an unused notebook. And a test circuit I built for my USB-projects. I just had to acquire a webcam, a push button like it’s used in moist rooms (how do you call that in english?) and two fluorescent tubes.

Unfortunately, I forgot to take a picture of the entire booth. It was basically a large box made of oriented strand board, about 2.20m high, 1.20m wide and 1m deep. On one side was the entrance, closed by a thick brown curtain. Inside there was a bank, opposed to it the technology.

Visible there were two simple tubes for the light, a rectangular section with a screen, a small round hole with a lens and said moisture-proof switch.

Hidden behind the wall were an IBM Thinkpad T43 along with a power supply, a Logitech Webcam Pro 9000 and some electronics.

I built this circuit since I didn’t want to make the same USB-interface over and over again on breadboard. It is essentially the same circuit as in my USB LED fader, the USB servo or my Dulcimer Keyboards. An ATmega8 microcontroller and some bird seed for the USB interface, at the other end a pin header to interface all unused pins of the controller on the breadboard.

The box was not built to last forever, so I just had two of the pins connected to terminal cables to the push button.

Software

The circuit is the same as the USB-Servo

The circuit is the same as the USB-Servo

In this project there are two important software components: the photo booth program on the laptop and the firmware on the controller.

The notebook was easy to equip. First I wanted to write a program myself, but after a short search I found something that does exactly what I wanted: Cheese. This is basically a photo booth. You press the space bar, then the program takes four images, at intervals of a few seconds. Simple and perfect.

The microcontroller was not quite as trivial to program, but I already had the solution in the drawer. With a slightly adapted Dulcimer firmware, the circuit behaves just like a simple USB keyboard. I just had to see in the schematic which pins I had to connect to create a space key.

:arrow: In combination with the moisture-proof push button I probably had the only wet room space bar in the world! ;-)

The combination worked perfectly: you go into the box and see the large display. After pressing the button, there were four consecutive pics taken, each with a short countdown.

The pictures end up in a directory and each has the recording time in the file name. That allows to rearrange the pics with a nice one-liner, so the result is a big picture with the full series of four images:

Results

Box of Fools

Box of Fools

I had assured that I would not put the images into the net, so there is only one unrecognizable example. The names of people and the original contents of the bottle are withheld. :-)

The quality has really surprised me. The camera makes really sharp and detailed images, and the fluorescent lights illuminated everything pretty evenly.

The box was used at the wedding-eve party and at the actual wedding. From the eve we’ve got more than 500 images, from the wedding even more than 800. Almost all the guests have found their way into the box, most of them repeatedly. And in packs: on some pictures we see at least seven people at once…

The curtain has proven to be a terrific feature. On many of the pictures you can see that the people did not expect that we can see the pictures lateron… ;-)

We are happy about each image. By means of that box, and above all the spontaneity of our guests, we have truly unique memories of one of the best days of our lives. Thanks again to all who joined us!

I didn’t have this article on my blog in 2009, it came over from my old CMS in 2015.

Test circuit on breadboard

Test circuit on breadboard

This project turns an AVR ATmega8 microcontroller into a LED controller for a matrix of 8×8 LEDs. The controller is acting as I2C-slave, so you can control the patterns to display via this bus (also known as TWI, Two Wire Interface).

Purpose

For my next project, I need to display number values on seven-segment-displays. I bought a bunch of 4-digit-displays a while ago, now I’m going to put them to a use. They are built with four digits in one case, and 12 pins on the underside. Eight of them are the cathodes of the segments (seven segments plus dot), four are the anodes. One for each digit.

You can imagine these modules as a matrix of four times eight LEDs, as can be seen in the included circuit. I use two of these, so I have a matrix of eight times eight LEDs.

The rows and columns of this matrix are connected to the microcontroller, so it can power them row by row. This has two advantages: at first a maximum of eight LEDs is powered at a time, so power consumption is lowered. And at second you need only 16 pins of the controller to address a total of 64 LEDs.

Driving the LEDs in this way makes them flicker a bit, but the controller is fast enough to keep the flickering way above the level you would be able to recognize.

I could have connected my display modules directly to the main controller of my next project, but I don’t have enough free pins on that. As a further benefit, multiplexing the LEDs on a second controller makes the main program easier to write, since I don’t have to mind the timing. So the solution is to use a cheap ATmega8 as LED driver and use the I2C-bus to tell it what to display.

I2C communication

The ATmega8 has a built-in hardware I2C-interface, so it doesn’t take very much code to use it. Nevertheless, I used a little library that Uwe Grosse-Wortmann (uwegw) published on roboternetz.de. I only reformatted it a bit to make the code resemble my style. It is well commented, but the comments are in german. Since only one global array, one init-function and an interrupt service routine are used, it shouldn’t be too hard for english-speaking people to figure out how it is used.

Usage

On the other end of the communication, I used the excellent Procyon AVRlib written by Pascal Stang. You can find it here.

The Circuit

The Circuit

Note: the buffer doesn’t contain any numbers that should be displayed on 7segment-displays. At least not in this example. It only holds bit-patterns.

Displaying numbers

If you solder 7segment displays to the unit and intend to display numbers or characters on it, you need to define them on the master-side of the bus. I didn’t include the definitions in this library because I want the master to have the full flexibility of displaying whatever it wants to, even if it are no numbers.

However, if you are going to use 7segment displays, definition of the numbers still depends on how you soldered them to the controller. I don’t know if the pin-outs are commonly standardized.

To give an example of how you would implement this, here is a fragment of code that defines hexadecimal numbers for usage on my displays:

Drawbacks

Till now, the device worked in all situations I tested it in. So far everything is fine.

Thanks!

I’d like to thank the authors of the libraries I used: Uwe Grosse-Wortmann (uwegw) for the I2C-slave and Pascal Stang for the Procyon AVRlib.

About the license

My work is licensed under the GNU General Public License (GPL). A copy of the GPL is included in License.txt.

Download

This text wasn’t part of the blog in 2009, I copied it from my old CMS in 2015.

My etching tank

My etching tank

Somehow I resisted to etch my own printed circuit boards for years. As I now know, I had no reason: it’s not as hard as I thought it would be. Having the right equipment helps with many things, so it does in this case. After having evaluated the whole process, one of the hardest things is to take off the rubber gloves after handling the chemicals…

Preparing the layout

One of my first own layouts

One of my first own layouts

Before creating the board, one has to create a proper layout from the circuit.

Many people use Eagle CAD for this job. It’s a great tool, but the free (as in beer) version has the handicap that it can only do layouts for half euro cards (that’s 8x10cm). You can do a lot of things on that amount of space, but at least for my Dulcimer project I needed more.

Meanwhile, I got used to KiCad. The usability is even worse than Eagle’s, but if you take your time and if you are kind to the program, it gives nice circuits and board layouts to you in return. And the killer advantage: it’s free software.

Exposure

Exposing the photo sensitive material is a bit tricky. I tried several methods, and I think I reached what I consider to be the optimum.

First the layout has to be printed. I made my first tries with simple paper, printing with my Laserjet 5. After not seeing any results on the boards, I tried coating the paper with oil to make it more transparent. Using a nitraphote lamp it would probably work with an exposure time of 50 minutes or so, but that seemed to be too long in my opinion. I got really good and quick results with overhead slides. With my first tries, I put two prints on top of each other, later I found that to be unnecessary, one layer is enough.

There’s even more choice with the source of light. What didn’t work at all was a 500W halogen lamp. Other people had more luck with that, but I guess that mine has a safety glass that blocks UV light.

A better solution would be the 250W nitraphote bulb that I acquired just for this reason. It’s a standard bulb with an E27 thread, but it delivers more UV than a normal lamp would. Unfortunately, 250W tend to be very hot after a while, and I almost ruined my kitchen lamp trying to expose through a layout printed on paper. After all, using the overhead sheet made really good results after an exposure time of 10 minutes in a distance of 15cm.

The best solution seems to be a facial tanner that I bought for 1,50 Euros — about a quarter of what I paid for the nitraphote lamp. It’s a Philips HB170, it has four tubes with 15W each. I turn it on for a few minutes, so the tubes are pre-heated. Then I put it face-down on two pieces of wood that are 3cm thick. Beneath it the stack consisting of the photo sensitive board, the printed layout and a glass plate. I turn the tanner on for two minutes and get great results — without risking to set the room on fire.

Etching

My first PCB

My first PCB

Surely, you can etch your boards in a simple lab dish, it shouldn’t affect the results much. But I didn’t like that method already on my first tries. Especially since it is everything but easy to maintain the temperature in the etching solution to be arount 50 degrees Celsius.

So I built my own etching tank. It was the cheapest solution since I already had some of the parts from my fish tank hobby. The etching tank consists of:

  • some sheets of glass
  • silicone
  • aquarium heater
  • aquarium glass thermometer
  • aquarium air pump
  • aqua-curtain air diffusor
  • air hose
  • parts of a cable channel (?) that hold the air diffusor and the board in place
  • a plastic container to put underneath the whole thing, since this is the first time I ever glued glass…

The tank holds about one liter of etching solution (natrium persulfate). The size fits quite exactly for one full euro card (16x10cm), the process takes about 10 to 15 minutes.

I am more than happy with the results. I didn’t make any detailed tests yet, but till now I found all the fine structures on my boards that I wanted to be there.