Play Games with Nixie Tubes, March 1958 Popular Electronics

Nixie tubes were used for numeric - and sometimes alpha - displays back in the days before LEDs and LCDs. They were more light bulbs than tubes, but were encapsulated in evacuated glass shells like vacuum tubes and had round, multi-pin bases like tubes. Separate filaments were provided for each character. There were two basic varieties: characters that displayed through the top of the tube, and characters that displayed through the side of the tube. "Play Games with Nixie Tubes" is the cover story for this March 1958 issue of Popular Electronics magazine. Nixie tubes are popular with builders of retro equipment, and a lot of products are available for sale that incorporate them; e.g., clocks, wrist watches, radios, clock radios, calendars, games, and much more. Electronic test equipment and medical instruments were big users of Nixie tubes. I remember a couple of the signal generators we used on the MPN-14 radar has Nixie tube displays. Supposedly the name "Nixie" derived from "NIX I", an abbreviation of "Numeric Indicator eXperimental No. 1," as designated by the Burroughs Corporation sometime around 1955. Nixie tubes for this project can be purchased on eBay.

Nixie Gamester installed in its grey aluminum cabinet. Activating button is in the center of the front panel.

Completed motor and wiper assembly - RF Cafe

Completed motor and wiper assembly.

Large gear with wiper wire in place - RF Cafe

Large gear with wiper wire in place. Small pulley and shaft are not used.

Commutators after etching - RF Cafe

Commutators after etching. The copper is entirely removed between segments. leaving ten 36° wedges of copper. Note bare 1/2" strip at bottom.

This simple form of digital presentation is made possible by a modern little electron tube called a "Nixie." Although specifically designed for computer panel read-out systems, the Nixie can be used in any device where any digit from 0 to 9 is to be displayed to a group of viewers.

By using two Nixies, a pair of tiny electric motors, two printed-circuit commutator boards, and a suitable power source, you can make up a game machine that will put new life in the dullest party, spark community and church affairs, and even help the youngsters in the house practice their arithmetic; All you do is push the button. Whirling motors flash the Nixie numbers inside the tubes too fast for the eye to follow. When the button is released, the motors come to rest, leaving two glowing numbers for everyone to see.

Numerical selection is accomplished by a wiper installed on the motor gear. As the armature rotates, the wiper arm contacts successively ten copper segments separated by etched grooves on a printed-circuit board which serves as a commutator.

Prepare the Commutators. Using a fine-toothed hacksaw blade, cut a single piece of 2" x 4 1/2" XXXP copper laminate board exactly in half. Make up a little cardboard wedge having an angle of exactly 36° with the help of a protractor. Using the wedge as a template, divide the laminate into ten equal segments of 36° each, and score the copper lightly with a sharp-pointed tool to mark the divisions.

Lay strips of 1/32" resist tape over the score lines and press their adhesive sides firmly down on the copper. Carefully paint the liquid resist over the entire board, leaving about 1/2" of copper exposed along the bottom as shown in photo above. Repeat this procedure with the second copper plate and set both pieces aside to dry for about a half hour.

The "Gamester" circuit incorporates a voltage doubler circuit to permit use of an inexpensive power transformer (TI) as a high voltage supply. The transformer's filament winding powers the miniature motors.

Finally, wash the plates in soap and water and dry them thoroughly. Drill a very fine hole in each segment as close to the outer edge of the wedge as you can work. Tinned hookup wire will be passed through each of the holes for wiring to the Nixie sockets as described later.

Hot It Works

Nixies. The Nixie 6844 is a gas-filled, cold-cathode numerical indicator tube having a common anode. Each of the numbers is a separate cathode which glows when a potential is applied between it and the common anode. Each tube contains a suppressor screen to minimize darkening of the viewing dome so that long life may be anticipated.

Anode Power Supply. A voltage doubler arrangement is utilized to obtain approximately 250 volts for operating the Nixies. Transformer T1has a double purpose: (1) it isolates the entire assembly from the a.c. line, thereby eliminating the possibility of electrical shock from the metal case to other grounded conductors; (2) it provides about six volts of a.c. which is rectified and used as motor drive power. Series dropping resistors R1 and R2 limit the current through the Nixies to a safe value. Before applying power, be sure that these resistors are in the circuit and that voltage cannot reach the tubes any other way but through R1 and R2.

Motor-Drive Supply. Six volts a.c, is taken from the low-voltage secondary of the transformer and rectified in the Mg-CuS bridge rectifier (BR1). This provides about four volts of d.c., which is more than adequate to run the motors within their ratings.

The motor mounting sketch above gives details of installation technique - RF Cafe

The motor mounting sketch above gives details of installation technique.

Nixie Games You Can Play

Bingo. This game is played in the usual manner. The players are issued numbered cards on which the numbers are crossed out as the Nixie Gamester reads them out. When all the numbers in any horizontal, vertical, or diagonal row are crossed out, the player calls out "Bingo" and is a winner. Unlike other readout methods, the Nixie numerals are clearly visible to all players.

Roulette. A good system to use for this game is the addition of numerals. For instance, if the Nixies show a 3 and a 6, then the winning number is 9. For double zero (00) or a double blankout, all points go to the bank. A large piece of oaktag divided into 18 squares makes a good roulette board.

Monopoly. Cops-and-Robbers, etc. Any game played with dice or a spinning pointer is a natural for the Nixie Gamester. Make up your own house rules as to whether the digits are added or subtracted.

Put-and-Take. For those who remember this game, the advantage of the Nixie Gamester over the old flat-sided top will be apparent immediately. Call the left Nixie digit "put" and the right one "take." The game is played with chips, marbles, picture cards, etc. A pot is started by each player contributing ten items. Then each player takes his turn "putting" and "taking" as the numerals dictate. A double zero or double blankout means "take all."

Party Games. The Nixie Gamester provides a new twist on the ancient games of "Spin the Bottle" and "Post Office." If there are ten couples at the party, each girl and boy are assigned a number (left-hand Nixie for the girls, right for the boys). A tantalizing spin of the motors, and a girl and boy are paired at random to go out and look at the stars. Should there be fewer than ten couples, certain lucky ones may be assigned two numbers, thus doubling their opportunities to have a chance at some social astronomy. In this game, a single or double blankout has no significance.

Quizzo. The group is divided into two teams. As the Nixie Gamester calls out the digits, the "left" team and "right" team must answer questions numbered according to the readout. Other variations of this idea are easy to dream up so that the party can be kept under full steam.

Mount the motor on the two pieces of wood which serve as base blocks. Note that the motor is screwed to a small piece of plywood which raises it enough to permit the gear to spin clear of the larger block. Using short wood screws, fasten the commutator board to the side of the base block so that the clear center of the segments is directly opposite the motor shaft. Thus, as the wiper spins, it will rotate in a circle having the center of the commutator as its center of rotation.

Another piece of the same spring wire serves as the contactor which rides on the back of the gear as the motor turns. It is held in place by another wood screw as shown and its pressure is adjusted so that it doesn't slow down the motor. It's a good idea, too, to connect the 100,000-ohm resistor at this time, holding it in place with a solder lug at each end. The resistors act as protective devices tor the Nixies and must not be omitted.

Power Supply Assembly. The Nixie Gamester is a.c.-operated. One low-cost transformer supplies the anode power for the numerals and the low voltage for the motors. A full-wave voltage doubler consisting of SR1, SR2, and the dual capacitor C1a/C1b comprise the anode power supply, while an inexpensive magnesium-copper sulfide bridge rectifier without filtering takes care of the motor drive.

All parts, except the push button and the Nixie sockets, are mounted on a sheet of perforated Bakelite. Wiring is completed outside the case and the finished assembly secured to the case by a long machine screw and brass spacer in each corner.

Wiring the Sockets. After you punch two 1" holes where the Nixies are to go, fasten the little glow tubes and their sockets in place with a 1 1/4" machine screw through each socket-flange hole. (The diameter of the Nixie is 1.080" so it cannot slip through the hole). In this way, only the face of each tube will be visible through the hole and the display will be much more effective.

Be sure to mount the sockets with pins 1 and 8 in a vertical line, pin 8 nearest the top of the panel. Pass a very short length (about 1/4") of the stripped end of hookup wire through each of the small holes in the commutator segments and solder to the copper faces carefully. Don't use too much heat. Trim the ends of the wire off after the solder has cooled.

The actual wiring should be done in a random fashion. Don't connect segment 1 to the socket lug for display number 1, segment 2 for number 2, etc. The numbers should follow each other haphazardly so that it will be impossible to force the motors to stop at any given place. Note that no connection is made to either pin 1 or pin 8 on the socket and that the common anode connection is pin 2.

To be sure that your Gamester will play a fair game, run through the following tests:

(1) Wiper contact. With power on, slowly rotate each gear by hand and observe the corresponding Nixie. Only one number should glow for each contact of the wiper on a given segment of the copper. If one or more numbers do not appear, bend the wiper so that it makes firmer contact. If more than one number is displayed for any single contact, it means that there is a bridge of copper between segments that was not etched away. A bridge like this can be picked off with a sharp point and the insulating groove cleared.

(2) Contactor. While each gear is manually rotated, observe the rear contactor to be certain that it maintains electrical touch with the rear face of the gear throughout the entire rotation.

(3) Motor spin. Motors should start instantly when the power is applied and should spin at high speed. If they don't do this, reduce wiper and contactor pressure by bending the wires back very slightly.

(4) Blankouts. The small contact surface of the wiper permits it to come to rest occasionally between segments. When this happens, the corresponding Nixie will not glow. Chances of both wipers blanking out on the same spin are very remote. You should, however, run through a number of spins watching for this kind of thing. If it happens too often, the wiper is catching on the edge of one of the segments as a result of excessive wiper pressure. A single blankout provides a one-digit readout and is desirable for most games in which the numerical sequence wanted runs from zero to 99 with no numbers missing.

Play Games with Nixie TubesMarch 1958 Popular Electronics

Play Games with Nixie Tubes
March 1958 Popular Electronics