7412533589

Readouts and Counter Tubes

By ED BUKSTEIN

Northwestern Television and Electronics Instiłułe

/Imporłanł adjuncłs for all electronic counting circuits: indicałors that give vi$ual łallies.

case), the next decade represents ten* (4+2+l=7 tens. or 70), the next hun-dreds, and so on. Thus the lights in Fig. IB indicate 26.179.

In Fig. 1C. five 10-lamp decades have been connected in cascade. Again the

Fig. 1. Neon readout lampa (or (A) pure binary counter. (B) (or (We 4-lamp dec-adei. and (C) (or fire 10-lamp decades.

• O ® O • # # O    *^NPUT

128 64    52 *    8    4    2 I

PULSE COUNT.i74 (A)

	® +
•	»
•	•
o •	- •-	INPUT

PULSE COUNT. 26,179 (i)

INPUT

PULSE C0UNT.47.62S (C)

Eoitor’» Notk : /« rarllrr aft iclca. Ihe aulhnr hns exylorcd Ihe rarlona lyyea of electronic counthiff circnifa and ihe i raya in i chich Ikry Work rathcr crtenairely. A'«ir hc funta to Ute maiicr o/ uarfully ertractiny in/onnalion ihey dereloy. Obnloualy indicators that make ihla tn/ornmtion rradily arallahle are nreded. There are many such, aa Ihe aut hor altowa

IT IS CHARACTERISTIC of binary and decade counting circuits that some of the tubes in them are below cut-off while others are at saturation. Which of the tubes are in each of these conditions at any given instant is determined by the number of pulses that have been applied to the input of the counter. Conversely. conditions of the tubes in the counter may be used to determine the number of pulses applied.

Earlier articles have shown how neon lamps may be wired into count-ing circuits to provide external indica-tion of internal conditions. In fact, neon lamps are frequently used as front-panel indicators on counters.

Some typical arrangements of such readout lamps are shown in Fig. 1. For a pure binary counter, lamps are num-bered, from input stage, 1. 2. 4. 8. 16. and so on up. with the total pulse count being obtained by adding the numbers of the lamps that are on. In the pure binary counter of Fig. 1A. 174 pulses have been applied to the input (128+32+8+4+2).

When a number of 4-lamp decade counters is connected in cascade, the neon lamps are arranged as shown in Fig. IB, with each vertical column of lamps representing another decade. Here, each of the five decades is as-sumed to be of the type consisting of four binary stages, with feedback net-works being used to re-set each decade on every tenth pulse.

The lamps lit in each decade add up to the digit for that vertical column, The right-hand column or decade re-presents ones or units (8+1=9, in this pulse count is determined by reading the “on” lights. but the task is madę easy because only one light at a time must be read in any vertical decade. Nevertheless, there is still a reading problem: except when the digits in all decades happen to be the same. the numbered lights do not appear in a single, horizontal linę.

For easier readability, several types of m-line readout devices have been developed. The front panel of an instrument using such a device is shown in Fig. 3. It is a digital voltmeter madę by Electro histrumeuts, Inc. In-line readout devices fali into three generał categories:

1.    The projection type. in which a light source is used to project an image of the desired numeral onto a ground-glass screen. In a variation of this type, lighted-line segments, instead of com-plete numerals, are selected and pro-jected in such a pat tern that they form the desired numeral.

2.    The edge-lighted type, in which the numerals are engraved on in-dividual sheets of lucite. The lucite shoets for a set of numerals are then stacked one in front of the other. A numeral is then selected for displaying by edge-lighting the sheet on which it is engraved.

3.    Multi-element electron tubes with built-in numerals that are madę to light up selectively by tubę action. These include Burroughs Nixie<g) and Pixie indicators.

The generał techniques for activat-ing projection and edge-lit readout devices are not too diflerent from those used with neon indicators. Tubes, however, are another mat ter.

Pixie & Nixie Indicators

The Pixie readout indicator is a gas-filled tubę containing ten cold cathodes located beneath a single disc-shaped anodę. As shown in Fig. 2, the anodę disc has ten perforations shaped like

57

October, 1959