building my own relay computer

Dave G4UGM dave.g4ugm at
Sat Feb 14 02:05:01 CST 2015

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at] On Behalf Of Dale H.
> Cook
> Sent: 14 February 2015 03:41
> To: cctalk at
> Subject: Re: building my own relay computer
> At 08:14 PM 2/13/2015, Ben wrote:
> The alu has never relay been a problem with relays, but what about main
> storage? Punched tape (paper/film/card) is no longer with us for I/O.

Punched tape is about. Check out the "green keys" list, 5-level stuff comes
up from time to time, generally at low cost. There is some ex-CNC items on
E-Bay at present but for silly prices. Whilst I haven't seen any on E-Bay
there were three Documation readers advertised on the Vintage Computer

> Fifty years ago I got around that by building my own card reader (very
> for input and hand-punching Hollerith cards with a hole punch. That was
> some years before I got access to an IBM card punch in high school. Output
> was a set of electro-mechanical counters, and they were a real pain to
> implement.

Many folks have implemented photo electric tape readers, but these tend to
be clocked off the small feed holes. I guess it wouldn't be too hard to
build a photo electric reader that has a 3-d printed feed wheel that was
driven by a stepper motor. In fact I am pretty sure you could even use a
coil and ratchet arrangement, like this one here:-

but operated buy a coil and magnet rather than a rotating cam. Some one has
actually made a complete but operated mechanical punch card computer..

so I don't think its hard. Getting things 3-D printed isn't hard, in fact
most FabLabs will have one and things can be printed for the cost of
materials. Also Hack Space...

 I think it's the punch that's harder. You would need to harden the punch
pins, and the would need to have a very exact fit. I guess a CNC router
could be used to make these...

Using a hand card punch isn't so slow once you get used to it, but these
also seem expensive...


> Dale H. Cook, Roanoke/Lynchburg, VA
> Osborne 1 / Kaypro 4-84 / Kaypro 1 / Amstrad PPC-640

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