Hours on gas-discharge indicators IN-12A
Hello. I want to tell you about my recent "hand-made article", namely the clock on the gas-discharge indicators (GRI). Gas-discharge indicators have long since sunk into oblivion, for me personally they are even the “newest” older. GRI was mainly used in clocks and measuring devices, later vacuum-luminescent indicators came into their place. So what exactly is a GRI lamp? This is a glass bottle (it's a lamp!) Filled inside with neon with a small amount of mercury. Inside, electrodes are also bent in the form of numbers or signs. It is interesting that the symbols are located one behind the other, therefore, each symbol glows at its depth. If there are cathodes, there must be an anode! - he is one for all. So, in order to light a certain symbol in the indicator, you need to apply a voltage, and not a small one, between the anode and the cathode of the corresponding symbol. For reference, I would like to write how the glow occurs.When a high voltage is applied between the anode and the cathode, the gas in the lamp, which was neutral before, begins to ionize (that is, a positive ion and an electron are formed from a neutral atom). The resulting positive ions begin to move toward the cathode, the released electrons, toward the anode. In this case, electrons “along the way” additionally ionize the gas atoms they encounter. As a result, an avalanche-like ionization process occurs and an electric current appears in the lamp (glow discharge). So now the most interesting thing, in addition to the ionization process, i.e. the formation of a positive ion and electron, there is also a reverse process, called its recombination. When a positive ion and an electron "turn" again into one whole! When this occurs, the release of energy in the form of luminescence, which we observe. Now directly to the clock. Lamps I used the IN-12A. They are not quite the classic form of lamps and contain characters 0-9. I bought a fair amount of lamps that were not in use!So to say, so that was enough for everyone! It was interesting to make a miniature device.The result was a rather compact piece. The case was cut out of a black acrylic laser machine using a 3D model, which was made on the basis of printed circuit boards:Diagram of the device. The clock consists of two boards. The first board contains four IN-12A lamps, a K155ID1 decoder and optocouplers to control the anodes of the lamps.Also on the board there are inputs for connecting power, controlling optocouplers and a decoder. The second board is already the brain of the clock. It houses a microcontroller, a real-time clock, a 9V to 12V conversion unit, a 9V to 5V conversion unit, two control buttons, a squeaker, and pins of all signal wires that match the display board. Real-time clock has a backup battery, which does not allow time to stray when the main power is disconnected. Power is supplied from the 220V-9V unit (200mA is enough).General view of the boards:These boards are connected using a male connector, but not by inserting, but by soldering!The whole thing is going this way. First a long screw M3 * 40. The tube from the 4mm air hose is put on this screw (it is tight and suitable for holding printed circuit boards, I use it very often). Then, between the printed circuit boards, the rack (printed on a 3D printer) and then the brass through-nut all this tightens. And the back wall will also be fastened with M3 bolts to through brass nuts.When assembling, such an unpleasant feature emerged.I wrote the firmware, but the clock refused to work, the lamps flickered in an incomprehensible order. The problem was solved by installing an additional capacitor between + 5V and ground right next to the microcontroller. It can be seen in the photo above (installed it in the plug for programming). I attach the project files in the EagleCAD program and the firmware in CodeVisionAVR. You can upgrade if necessary for your own purposes))) The clock firmware is made quite simple without frills! Just watch. Two control buttons. One button is “mode”, the second is “setting”. By pressing the "mode" button for the first time, only the digits corresponding to the clock are displayed, if in this mode press "setting", then the clock will start to increase (when it reaches 23, it is reset to 00). If you click on “mode” again, only minutes will be displayed. Accordingly, if you press in this mode “setting”, the minutes will also increase in the “circular” order. With one more click on the “mode” - the hours and minutes are displayed. When you change the hours and minutes, the seconds are reset.
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