Printed Circuit Origins… or…Cutting Board Computing

Exterior view of wall phone common to the 1880’s through early 1900’s period.

One of the things I have collected and tinkered with over the years is old phones.  WWII field telephones, 1930’s and 40’s art-deco dial phones, etc….and I still use a couple of vintage rotary dial phones in the house today.  Recently I picked up an old phone from my childhood–this is an 1890’s vintage wall phone that had been in my grandfather’s home for many years.  Aside of the specific antique phone appeal and the sentimental value to me, this old example of communications technology also exhibits a construction technique with a direct lineage to modern printed circuits.  The breadboard.

Perhaps you have heard the term, “Breadboard”   …or perhaps not.  This term generally refers to building up prototype or test circuitry.  These days, small socketed boards that are solderless and easy to reconfigure are often used for small projects and for teaching purposes.  The design of such a “breadboard” dates to the late 1960’s/early 70’s.

Prior to this, however, such devices were built up using point to point wiring and the components were often mounted atop a wooden board.  This wood board was the original breadboard.  If it were a kid’s project, it was also entirely possible that the breadboard in question was removed from mom’s kitchen….and she may not have been happy about it!  These initial breadboards were used for slicing bread and were essentially what we would recognize as a wooden cutting board today.  (now you know where “breadboard” gets its name……that and why my own mother would have been ticked off at me at least once)

For the most part, this building technique has been limited to one-off sorts of projects.  But this was not always the case.  In the early 1920’s, companies such as Atwater-Kent produced wonderfully made radio receivers with exposed components built atop a wooden plank.  Such breadboard sets command a high price today.

Example of Atwater-Kent breadboard radio, ca1920 (image from web)

1920’s radios were far from the first commercial use in production of the breadboard construction methodology.  That honor most likely would have to go to the early telephones of the 1880’s.  Very likely these are the first “mass produced” electronic device intended for consumer use.  Sure, the telegraph predates the telephone by a few decades–but telegraphy required specialized training and was limited to those in the business of handling message traffic.  The telephone, however, quickly found favor with the general public and soon spread from the general store and into individual homes as well.

Internal view. Note the wiring through the hinges and the later modification of the added zip cord.

The early wall phones utilized a hand crank generator for ringing the bell at the switchboard, a set of batteries to power the microphone and speaker contained in the handheld receiver, a bell, hook switch, induction coil, and condenser.  Very simple.  In those days, the wiring was done with bare, tinned copper that connected between the components.  When these non-insulated wires would have need to cross due to mechanical layout constraints but could not be in electrical contact with one another, they simply passed through to the back or bottom side of the wood structure and were routed there.  Where a turn needed to be made in the routing on the board and no connection point existed to hold the wire in place, they simply added a small pin and routed the wire around it with a dab of solder to hold it there.  In the case of these phones, wiring that needed to go to a part mounted on the hinged cover utilized the metal hinge as a connection point.  A close look at this breadboard style of wiring layout shows a direct ancestry to the printed circuit boards of today.  It is no great leap to imagine a computer wired in much the same manner.

View of wiring on the backside, note similarity to modern printed circuit board concept.

For this phone…At some point, probably in the 1970’s when this phone ended up on display in my grandfather’s home, a piece of modern zip cord was added to enable the generator to ring the bells directly.  I remember spinning the crank just to hear those gongs sound off!  You see this in movies a lot, but it is actually not right.  The original wiring would have the bell at the switchboard ring and would not have also rung the local bell if you turned the crank as the hookswitch and the switch in the generator itself would have prohibited this.–but the modification makes for good show and I will attest to the fact that a kid loves it.  Since this example is otherwise complete and unaltered, it will be a simple matter to remove the zip cord jumper and get the set back to original configuration.  I may end up doing this, since it would also be easy to replace the receiver cord and get it to work with the EE-8 field phones from WWII that I have…..perhaps one will go into the house and one into the shop as a working intercom of sorts.

“Number please?”

 

2 comments

    1. You are referring to EXchange names. I still use them sometimes. Usually they were comprised of two capitalized letters that began a name (PEnnsylvania, for example) The letters, as you likely know, corresponded to numbers on the dial…hence PEnnsylvania6-5000 would have been 736-5000. Often the name used denoted the location of the phone company’s switch office that served the area. (Pennsylvania Ave perhaps?) You can, of course still use the format today….I often do, although sometimes it obliges me to explain myself.

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