Required. Whereas in the previous design a separate

display device with suitable decoding circuits. In the

present design consideration will be given to the RCA

numitron type DR2000.

The same decade counter with b.c.d. (Binary Coded

Decimal) outputs as used in the first design will

function here but a different decoding circuit is

Bottom view of numitron.

Fits into a 9 pin miniature

^/valve socket

.+4.5V

^-Pin 1 is not used

RCA OR2000

+ 4'SV 1.16

OR2000 6" 8S 4

1 15 114 1 113 1 112 1 n no

CD2500E

ii u m m m 1 12 13 4 5 16 7

Input pulses Oj 2V

'

i i

=+

'4 13

a

Close "/ to test / numitron V

lioi II

SN 7490

1 2 34

5 6

Reset

--ve

t

Fig. 2: Shows the interconnections of the units using the CD2500E decoder.

required. Whereas in the previous design a separate

pin was needed for each numeral, here only seven

are required and a b.c.d. to seven segment decoder

is used--RCA type CD2500E.

Once again the complexity of the internal circuitry

of this i.e. makes it impractical to draw so Fig. 2 shows the interconnections of the complete unit. A

suitable printed circuit board pattern should not

prove too difficult for the competent constructor and use could profitably be made of the new dual-in-line

mounts advertised by some firms in this magazine. In addition to providing easy insertion and removal of

the i.c.'s they also prevent damage to the i.c.'s from excessive heat in the soldering process.

Needless to say, numerous uses can be visualised for these counters. The 50Hz mains can be used as a

frequency standard to make an accurate interval timer when coupled through an AND gate to the counter. Also interruptions in a beam of light or

pulses from a geiger tube to determine the activity

of a radioactive sample can be counted.

A very welcome development related to this field

is the drop in prices of the new Gallium Arsenide solid state light emitting diodes. Single devices of this

type can now be purchased for around ?1.50. With no filament to worry about they are exceptionally robust and have an exceedingly long life span. Arrays using upwards of fifty of these arrayed in a 5 x 10

rectangular matrix are used in many alpha numeric

readout systems and recently the first all electronic

solid state wrist watch with digital readout has been

released in the U/S. using four of these arrays. If the present trend continues they will certainly offer fascinating possibilities for the home constructor in

the not too distant future.

IC type SN7441A and SN7490 are available from

Bi-Pak Semiconductors.

IC type CD2500E and numitron DR2000 are avail-

able from:--Roberts Electronics Ltd., Hermitage

Road, Hitchin, Herts.

Hivac Numicator type XN24 available from: --

Hivac Ltd., Ruislip, Middlesex.

DECCA 3000 HI-FI SYSTEM

WON BY BRISTOL READER

OF 25 YEARS STANDING

A reader of Practical Wireless for 25 years has won the Decca Hi-Fi System Competition which was featured in our November Issue. He is Mr. Dyke of Bristol. At a recent lunch held by l.P.C. Magazines to congratulate Mr. Dyke, it was revealed that he had taken to reading the magazine after the excellent results he had found with a home-built 2-valve radio designed by F. J. Camm, an earlier Editor of P.W.--and he has hardly missed an issue since.

Mr. Dyke is a great fan of "Practically Wireless" by Henry and rates F. G. Rayer amongst his most popular authors. Being an 'old-timer' in the construction game he is also a keen follower of "Going Back".

The entry which secured the Hi-Fi System for Mr, Dyke was: 1-J, 2-K, 3-1, 4-E, 5-A, 6-D, 7-B and 8-C. The entry was the only correct one out of several thousands.

The Hi-Fi System was something Mr. Dyke had wanted for a very long time and it is the first prize of any value that he has ever won!

1052

A

Norman Stevens on the 'eft, Editor of Practical Wireless, congratulates Mr, and Mrs, Dyke on winning the Decca 3000 HI-FI System.

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