Standardised printed circuit units for digital computers
Denis L. Johnston · 1952
The optimum size for a plug-in arithmetic circuit unit was found from experience to be 4-6 valves, which can be accomodated in printed circuit form on a glass plate 3″ x 5″ with silvered edge contacts used in conjunction with a conventional in-line socket.A standard pattern of 72 holes was adopted, and it has been possible to lay out 15 different circuits about this matrix, while using only one set of processing jigs. Sprayed film resistors and tablet capacitors occupy standard positions between holes, and the resistors are brought to the correct value by a servo-operated engraving machine. In this way a large number of different resistance values can be obtained in a circuit with only one or two spraying operations.Automatic processing techniques have been worked out for each major operation in the manufacture of the circuit units, with the object of realising the uniformity and consequent reliability that follows from the adoption of continuous processes and quality control methods.