Category Archives: electronics hobbyist

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

Arduino, electronics hobbyist

Geiger counter and radioactivity

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One project that had long been of interest to me was the detection of radioactive radiation. After the horrible powerplant accidents in Japan, this idea was recalled. I could still vaguely remember owning an unused counter tube somewhere in my old workshop cellar. – After some search it turned up :). Thanks to the Internet and the search engines, a data sheet was also found quickly. The counter tube is a ZP1400. A self-extinguishing Geiger-Müller counter tube with mica window. The tube is according to data sheet with neon and argon filled as quenching gas. The operating voltage is 400 to 600V. The capacity between anode and cathode is about 2pF. With these and other information from the data sheet i now can tinker a circuit to take the tube in operation. I have used this small project to introduce our apprentice to the board layout at the same time and to get acquainted with the creation of small programs on the Arduino Uno microcontroller board. In this post I introduce only the “old-fashioned” circuit, where only the impact of ionizing radiation is made audible to the count wire. (the typical crackling). This circuit then provided the basis for the apprentice to realize the count of the pulses with the microcontroller and to visualize it on a two-line LCD.
Wiring diagram with high voltage supply and pulse amplifier

Using the well-known layout software Eagle, I have drawn a circuit in which the high voltage is again generated by a switched transformer and subsequent Greinacher cascade. The control takes over this time no 555er, but simply a feedback Schmitt trigger. The time base is set via the coupling resistor and the capacitor. Thus, the high voltage is available for the counter tube. In order to be able to count the impulses, two factors are ensured. The impulse must not exceed a certain height. (Otherwise the following electronics may die) and the pulses should be audible (boosted). So the peaks are limited with a zener diode circuit and put into a “nice” shape with Schmitt triggers and then led to an op amp. At the output of the op-amp then hangs first a small speaker …

Arrangement of components on the PCB

After the circuit board was etched and assembled, it was time to test. But with what? I needed some weak source. I held all sorts of items in front of the counter, but it did not change much. There was a cracking sound from the speaker four to eight times a minute. So I started researching the net again. And came across the term “radium color”. This is the self-luminous color with which the dials of old watches were painted, in order to be able to read the time even in the dark. This information gave me an idea. From my grandfather i inherited once an altimeter of a WW1 aircraft (manufacturer LUFFT) whose dial might have been painted with that kind of color. So get out of the showcase and held in front of the counter tube … The result can be seen in the video.

 

 
electronics hobbyist

The oscilloscope picturetube

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At the beginning of my blog, I talked about a small project with an oscilloscope tube. Since there are still pictures in the archive, I do not want to withhold it from the blog here:

Cathode ray tube with high voltage generation


A cathode tube (Braun tube) consists of an evacuated glass bulb in which a hot cathode of tungsten wire is heated by an electric heating wire. The electrons emerge from the surface as a charge cloud (annealing emission). Between the positively charged anode and the hot cathode there is an electric field in which the electrons are accelerated. A pinhole allows the approaching electrons to pass only a bundle of determinable diameter, the actual electron beam. The electron beam can then be further accelerated.
The Braun tube – as it is e.g. is present in a cathode ray oscilloscope – has two capacitor plates each to deflect the electron beam. (X and Y baffles). The tube is a Philips B7S 401 oscilloscope tube. For the sake of completeness, I list some technical data here:
  • Indirectly heated cathode, heating voltage Uf = 6,3V
  • Heating current If = 90mA 
  • time for heating kathode tK =1min
  • total accelerationvoltage Ua= 1,2kV
  • Base point tension of the post-acceleration resistance Ug5 = 300V 
  • acceleration voltage Ug4 = 300
  • focusing deltaUg3 = 20V … 50V
  • pre acceleration volatage Ug2 = 1,2kV
  • reverse voltage Ug1 = -30V … -80V
Connections on the tube socket

The aim of the project was therefore to put the small tube back into operation and to lure her a few pictures. So a drive had to be built. Since the supply voltages are quite varied (6.3V to 1200V), this problem had to be solved first. With a NE555, a few components and an old transformer (240 / 12V) a high-voltage power supply was tinkered.
The principle is simple: A DC voltage is switched on and off very quickly with a small circuit. This switched DC voltage in turn connects with a power transistor, the output side of the transformer. (ie where normally the 12V are applied now fed) The ratio of the transformer works in the other direction :). So arise at the exit ever a few hundred volts. (depending on the switching frequency). In order to produce over 1200V, I have connected a cascade (capacitors and diodes). (Functionality)
So now all voltages necessary for the operation of the tube are available to produce an electron beam. With the aid of adjustable voltage dividers, the beam current and the grids for brightness and image focus can be set.

the fist illuminated spot

The voltages for the baffles are also taken from the high voltage supply and controlled by transistors. Thus, a deflection of the electron beam in both axes is possible.

Plexiglas housing

The transistors in turn are controlled by a small pre-stage, which is fed externally with a voltage of -5V to + 5V – the control voltage for the deflection of the light spot. This control voltage input exists for both axes. I added another input to switch the electron beam to “bare”, ie dark. For this purpose, a corresponding voltage is applied to the corresponding grid, which previously block the electron current to the anode.

connections

Thus, the tube can now be controlled directly from the outside, for example, by means of analog outputs of microcontrollers (Arduino, PIC, etc.) or NI DAQ cards with the extra-low voltages available there. After the first positive test runs with the breadboard electronics I then constructed a clean board and mounted the whole construction on a wooden board and covered with a transparent Plexiglas housing.
All connections are routed via banana sockets to the outside. For example, you can easily draw Lissajous figures on the screen …

Lissajous-figure done withe NI-DAQ
electronics hobbyist

F101 Voodoo Radarmonitor

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From a McDonnel F101 Voodoo came the following sample that I got from a customer back then, with a request to try to bring it back to life somehow.
The thing I’m writing about was a black cylinder about 30 centimeters long and about 20 centimeters across. On one end face of the cylinder was a picture surface as seen from an oscilloscope, with a rotatable scale ring with a 0 to 360 degrees angle label.
The customer told me it was the cockpit radar of a Starfighter jet. Then I began to research what turned out to be relatively expensive at that time, in the mid-90s, especially since the Internet did not yet exist in the form and diversity as it exists today.

picsource: Wikipedia

But at least I found out that the part was really the board monitor of the radar system of an airplane. Namely to the radar monitor of a McDonnel F101.
A twin-engine fighter aircraft of the 50s cold war US Air Force.
In any case, the part came from this plane – wherever the customer had it from. And he asked me if I had any chance of getting it up and running. He meant that he wanted to see the famous, rotating light stroke on the screen.
At that time, I could not find any information or documentation on the part, how to connect the tangle of cables over cables, which came out of the device …

 
frontview of the monitor

So I started dismantling. Several miniature electron tubes, transformers and many smaller tubes with bobbins with immersion cores and many, many capacitors were installed. In the longitudinal axis of the device, the picture tube was housed, with the magnetic deflection was rotatably mounted about the axis of the tube. Say, the complete deflection unit was turned around the tube by means of an electric motor drive.

topview

Since I had no chance to somehow understand the circuit, especially since apparently some components, such as the entire voltage and signal conditioning were not integrated in the monitor, but apparently were installed elsewhere in the plane, so I set out to dismantle everything. All that was left was the picture tube with the mechanics and the deflection coils and the drive. On a breadboard I started to make my own drive for the coil drive. For the deflection coil itself, I built a sawtooth generator with a sufficiently strong power output stage. And for the high voltage of the tube had to serve an old line transformer of a television, which was driven by a NE555 (the old known timer module) and a matching power transistor (some BU508 …).

and it´s turning again

The whole circuit was operated at about 24V and took over 2A. (including cathode heater and electric motor and the scale bulbs that illuminated the labels).
But it worked. On the screen was a green line, which turned at the adjustable rotational speed. That was already everything. There was no beam modulation or the like to draw any simulated radar images. Today you could work together with small microcontrollers like Arduino and co, quite simply …