5 Mar
2004
5 Mar
'04
8:04 p.m.
Tony wrote:
There have been several designs for homebrew readers, the schematic of
one is in the back of the S100 handbook. The unidentified chips in that
schemaitc are obviously 555 timers, used as schmitt triggers (!). The
only difficult thing to make is the photodiode array for the read head. I
wonder if you could use plastic fibre-optic cable to lead the light from
a row of holes to some normal-size photodetectors mounted on a PCB in a
convenient arrangement. It would be easier than finding some
photodetectors that you could mount on 0.1" centres.
One further catch if you are building a tape reader ... or doing a "radical
rebuild"* on a very old design: make sure that the power to the light source
is reasonably well smoothed ... an AC ripple here can lead to mysterious
inconsistencies when trying to read tapes :-)
* before Tony is inclined to accuse me of vandalism here, I'll mention that
this "rebuild" took place 20 more than years ago when I acquire a couple of
old (then!) ex-mainframe tape readers and converted most of the electronics
from discrete (which I didn't understand) to TTL
(which I could get to work)
to interface to a home-brew 6800 system.
Andy