Browse over 10,000 Electronics Projects

# Inside Card Sorters of 1920s – Data Processing with Punched Cards and Relays

## Relay logic

Unlike the older sorters, the Type 83 sorter reads the entire column before selecting a bin. This lets it, for instance, reject erroneous cards with multiple punches in one column. How does it detect multiple punches? Instead of using logic gates built from tubes or transistors, it uses a network of relays. This section describes how relay logic works.

IBM relay (permissive make type).

A relay (shown above) contains an electromagnet coil that moves contacts, switching circuits on or off like a toggle switch. In a typical relay, the circuit connects to the “normally closed” pin when the relay is inactive, and connects to the “normally opened” pin when the relay is active. A relay may have multiple sets of these contacts. The diagram below shows how a relay appears on IBM schematics. On the left is the electromagnet coil, and on the right is one set of contacts. The diagram shows the inactive state, with the center wire touching the bottom contact. When the relay is energized, the center wire moves and touches the top contact, switching the circuit.[8]

Symbol for a relay: relay number 9 and contact set 2.

The diagram below shows the relay circuit in the sorter that counts the holes and determines if zero, one, or more holes are present. With no holes (top), current flows along the bottom path. A single hole (middle) energizes a relay (#7 in this case), transferring current to the middle path. The next hole (bottom) energizes a second relay (#5 in this case), transferring current to the top path. Thus, this chain of relays determines the number of holes present, and erroneous cards can be rejected.

Relay network in the IBM Type 83 card sorter. This circuit determines if the card has 0, 1, or more holes.

A more complex relay circuit was the optional faster alphabetic sorting feature available on the Type 83 sorter. For an additional \$15 a month rental fee, customers could sort the most common letters in one pass, saving time while sorting. This circuit used several large relays, each with a dozen sets of contacts (an unusually large number). These relays decoded the hole pattern to determine the specific character and then selected the appropriate bin. The diagram below shows a small part of the circuit; click for the full diagram.

Detail from relay network for enhanced alphabetic sorting in the IBM Type 83 card sorter.

The photo below shows the wiring on the back of the relay panel. The wiring in the sorter is all point-to-point wiring, rather than printed circuit boards. Note that the wires are carefully laced into neat bundles.

Wiring inside the IBM type 83 card sorter. This is the back of the relay panel.

Pages: 1 2 3 4 5 6 7 8