Nixie clock - modern electronic watches

What does most modern electronic watches look like? It is easy to imagine a plastic case, segment numbers on a gray LCD board, or glowing on an LED. Without a difference, they are all very ordinary and similar to each other, like two drops of water. For the manufacture of our neon clocks, we turn to the era of cybernetics, and make them according to the most out-of-date technologies!

The prototypes of the neon indicators, world-known as NIXIE, were developed in a small laboratory of the manufacturer of electrovacuum devices Haydu Brothers Laboratories, which was subsequently purchased by Burroughs Corporation together with its trademark NIXIE. And in 1954, indicators were introduced to the market. The name NIXIE was derived from the abbreviation "NIXI" [Numeric Indicator experimental No. 1), and firmly established in the everyday use to denote neon gas discharge indicators. It should be noted that the first serial indicators appeared in the 1930s, but at that time their use was severely limited by the rough design of the devices themselves and the still insufficiently developed element base. And the very first indicating devices, working on the basis of the principle of a glow discharge, were patented in 1920, when, after the invention of radio lamps, a powerful and intensive study of electrical processes in vacuum and strongly diluted gases began.

In any case, it is better to buy such a watch on https://millclock.com/en/, what to make them yourself.

How NIXIE works

Neon indicators are low-pressure gas discharge devices that operate on the basis of glow discharge processes. Before proceeding to an explanation of the principle of the operation of gas discharge devices, let us consider the process of passing an electric current in a gas. Under the influence of a strong electric field, electrons from the atoms of the inert gas are torn to the anode, and the remaining positively charged ions are directed to the cathode. This process is called breakdown of the gas column. Then, as a result of intensive bombardment of the cathode by positive ions, secondary electron emission begins, and a stable glow discharge arises. Simultaneously with the process of gas ionization, an inverse phenomenon occurs, in which ions are converted into neutral atoms. The transformation of gas ions into neutral atoms is called recombination; In this case, energy is released, under the action of which the ionized gas glows.

Directly to the cathode 1 is a thin, thickness of fractions of a millimeter, astonovo dark space 2. Here the electrons knocked out of the cathode have not yet had time to acquire enough velocities to excite the gas atoms, so there is no glow in this region. Next is a luminous film 3 in which the accelerated electrons excite, but not yet ionize, the atoms of the inert gas. Excited atoms emit quanta of light with a color of luminescence characteristic of this gas. Thus, a glow discharge in neon is accompanied by intense red-orange light.

Then follows the dark cathode space 4, in which the ionization of atoms begins, and electronic avalanches also increase. The positive ions formed in this region are carried back, bombarding the cathode and causing secondary electron emission. A large number of fast avalanche electrons attack the next layer. It begins with a sharp luminous boundary and is called the region of a glowing emission. Here, electrons recombine with positive ions.

The burning glow gradually turns into Faraday's dark space 6, where fast electrons, born by electron avalanches, no longer reach. This space is followed by a positive column of discharge 7 occupying the entire remaining region up to the anode 8 and luminous due to the recombination processes. The voltage at which a glow discharge is formed is called the ignition voltage. It depends on many factors, such as the composition of the gas, the pressure, the distance between the electrodes, their material and shape. The phenomenon of a glowing film near the cathode is based on the work of gas-discharge indicators. The neon indicator is a glass bulb with a set of sealed electrodes filled with depleted neon. The anode is made in the form of a glass covered with a grid, and a positive potential is applied to it. Cathodes in the form of a wire are formed in one of ten Arabic numerals and placed inside the glass. If negative potential is applied to one of the cathodes, the inert gas begins to glow around the wire. Technologically, the pressure inside the balloon is selected so that the glow turns out to be uniform and bright. Thus, by supplying voltage to one of the cathodes, it is possible to "flashing" any digit from 0 to 9.

Each decimal output is equipped with a high-voltage transistor with an open collector. In other words, cathodes of neon indicators can be directly connected to the same outputs of this chip. The control of the indicator itself is reduced to feeding the binary code of the ignited digit to the four address lines of the decoder. Despite the fact that it is a very old school microcircuit, in the former USSR, they, as well as the indicators of the IN series, were released up to the year 87, while they were long ago abandoned abroad. That is why it is easier to get this "Soviet good" all over the world now than brand analogues. In addition, the cost of these four chips can not be compared with the cost of four tens of high-voltage transistors (40 rubles against 400).

As the controlling controller AVR - microcontroller ATtiny26 of firm ATMEL is chosen. Description of the principle of operation and architecture of these microcontrollers is not within the scope of the article - there is a huge amount of information on the topic. Strictly speaking, ATmegaS would be better suited for our purposes. But consider another option, besides not inferior in price.

To control the indicators we need 16 pins (4 indicators for 4 lines), one more pin is needed for flashing points, two will be used for quartz, and two more pins will be required for the buttons. Total - 21 conclusion. To increase the missing pins, we use an external 8-bit SN74LS373 latch register (domestic analog KR1533IR22), and connect it parallel to the main port A, and one output from port B is used for fixing. The indicators are connected in pairs - one pair to the latch register, the other to the controller. Now, to set all four digits on the neon indicators, you need to do the following:

1. set the output of the STB register-latch log. 1.;
2. write in port A codes of units and codes of tens of hours;
3. Set the output of the STB log. 0, thereby fixing the data in it;
4. write in port A codes of units and codes of tens of minutes.

This whole sequence will be executed by the microcontroller in a few microseconds. The power supply is made according to the classical scheme. As a network transformer, a compact 7-watt TTP-110 is used. From the rectifier BD1C1C2, an unstabilized voltage of 12 V is applied to a boost converter and a linear regulator L7805, which supplies the digital part of the circuit. All other blocks, with the exception of the indicators themselves, the installation of which is planned on the front panel, are placed on one single-sided printed circuit board. The buttons for setting and setting the clock will be located on the rear panel together with the power connector and are structurally integrated with the ISP-connector of the microcontroller programming.

Full version of the circuit with a picture of the printed circuit board, photomasks, source codes and finished firmware search on the disk.

Housing for NIXIE

Making such neon clocks on old-fashioned neon indicators, it would be untenable to place them in some trite plastic box. IN-1 - this is the first domestic gas-discharge indicators from the era of cybernetics. Almost all of them are crooked, slanting and very brutal, so they require a suitable body ... ideally of black bakelite with a finger thickness, or concrete, such as NIXIE Concrete Clock. In Daniel Kurt it was just a concept, we will make it into life! Since the corps claims the right to be fundamental, then we will do it according to all the rules of making foundations.

Formwork and casting of the second wall

Neon watches with their own hands
Of course, we will not use real concrete. This is unreasonable, because the time of his grasp is several days, and he attains full strength only in a month. Instead of concrete we will use building plaster (alabaster). Working with it is much easier, the mixture will harden in 10 minutes, and will have a smooth surface with a rough texture, pleasant to the touch. Casting the hull is done in stages - each side separately. This requires a large piece of glass and a few strips of tin. Glass serves as the basis, and strips formwork. Strips, about 0.5 mm thick, are fixed at the corners by flat magnets from the outside, thus an easily disassembled multiple-use design is obtained. First, the geometry of the workpiece is marked on the sheet of paper, after which the sheet is placed under the glass. Then, along the lines of the future borders of the "cover", tin formwork is fitted. After that, the gypsum is dissolved to the consistency of liquid sour cream and poured into the resulting form. The time of thickening is only 2-3 minutes, therefore it is necessary to work very quickly and accurately. Using a spatula, the mixture is spread out over the entire mold. After 7-10 minutes, gypsum hardens. The workpiece becomes warm and durable. Now the formwork is dismantled and it is possible to start separating the workpiece from the glass. So we got only one wall. The remaining walls of the hull are formed in the same way. First of all, it is necessary to try on the preform already available to the newly formed tin formwork of the next side of the future case, so that it can be easily inserted there, and the walls of the formwork fit snugly. First the gypsum mixture is poured, and then the workpiece is inserted, and the workpiece should lie still for about 10 minutes - otherwise it will not get even joints. While the gypsum is warm and wet, has not yet gained full strength and it is easy to scrape, you need to quickly remove all surplus. If there are "slits" between the sides, or when a shell is formed, then after complete solidification of the shell, they can be easily "healed" with a spatula, a dry mix and a small amount of water. The bottom is done in the last place, after making holes for the neon indicators.

The contour of the holes is drawn by a compass on the plaster. Then several holes are drilled in the center, and the core is gently squeezed out. Only no punches! Up to the desired diameter, everything is done with a thin-walled scraper tube. The holes are ready and you can start casting the bottom. Gypsum is a porous material and behaves similarly to a heater, therefore for a normal work of electronics the back cover should not be done.

Inside, the gypsum still remains wet, and so that the body does not move, before installing the electronics, you need to leave it for a week in a warm place. In the drying process, the body changes color from dark to light gray. When the gypsum is completely dry, you can proceed to fix the neon indicators in the holes with glue. On the lower plane of the concrete watch case rubber feet are glued, and the watch is ready!

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