2021-01-24                             dispatches from helix
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   Planning stages for a new plugin for my Tektronix 5110
   mainframe oscilloscope. I have traced all of the pins on the
   card-edge connector from the (ample) technical documentation
   and think I know enough to have a go at a custom Y axis
   plugin and _maybe_ an X axis one.

   The connector which matches the specification for this
   1970's scope is actually obsolete (shock!) but it looks like
   it's physically compatible with the JAMMA connector used by
   arcade machine enthusiasts and readily available on eBay. I
   have two finger boards and sockets coming from Markham,
   Ontario.

 I already have (but which is quiet).

   A recent impulse purchase of a magnetic-loop antenna has
   kicked this off again for me, after I gave a lot of my ham
   stuff away. It just seemed like a hobby I was past -- I
   don't actually enjoy talking to other operators and racking
   up QSOs, I like building radios -- but I suck at it. However
   enough time has passed and I've gotten better at building
   _audio_ frequency analogue circuitry, I think I am ready to
   give RF another try.

## 💡 Electronics

   Of course, I actually already had an analogue scope. Two. I
   won the cheapest CRT scope I could find on eBay back in 2019
   and they sent me the wrong one. I contacted them about the
   mistake and they sent me the right one, and let me keep the
   one they already sent. (CRT scopes are heavy, didn't make
   sense to courier it back to Washington state).

   They are in the Tektronix 5110 range -- 2MHz entry level
   mainframe scopes. Mainframe means that it's a little like a
   modular synth: the scope is actually reasonably dumb, mainly
   consisting of the power supply, CRT and deflection
   amplifiers. The real smarts are provided by up to three
   plugins you slide into the front of the chassis.

=> https://w140.com/tekwiki/wiki/5110
 > Tektronix 5110 TekWiki Page on the Big Web

   The plugins in slots 1 and 2 are designed to amplify or
   attenuate signals for the Y axis. The plugin in slot 3 is
   designed to provide a time-base (basically, to move the beam
   from left to right a certain number of times per second).
   You can use one of the vertical plugins in slot 3 to make an
   X-Y display, which is actually the main reason I wanted the
   scope in the first place.

   I have various plugins that came with the two scopes, but
   they range from "suspect" to "definitely faulty". At their
   very core, though, the vertical amplifier is basically an
   op-amp with a +/- 30V range, and the time base is a variable
   rate sawtooth wave generator (with a comparator for handling
   the trigger function). X and Y position controls are
   literally just adding or removing DC bias.

   So, I've decided it'd be fun to build my own plugins, based
   off of modern ICs. I've spent the evening going over the
   manuals and tracing the function of every pin on the
   connectors. (Fun surprise: pin A1 is 200V! This is just used
   for lighting up an optional neon light, as this scope comes
   from the era before LEDs)

   Before going and fully designing a board, I wanted to be
   able to trace one of the amplifiers that I have while it's
   in use. I needed an extention board. Needless to say, Tek
   ones are unobtanium on a 40-something-year old device that
   wasn't even _that_ popular to begin with.

   I measured the parts I have an searched on Digikey for 56
   connector 0.156" pitch edge card sockets. There was exactly
   one match. The minimum order was 480 (~$8000) and the lead
   time was 13 weeks. Ouch.

   As a last ditch, I tried putting 56 connector 0.156 into an
   eBay search and discovered that these sockets are the same
   ones used by the popular JAMMA arcade machines. There's an
   active hobbyist scene around these and connectors can be had
   for $4. I have some coming from Markham, Ontario, they
   should arrive next week.

   This project is going to take a little time, and in the end,
   it'll be pointless, but actually I think I am okay with
   that. I've already had a really enjoyable evening trying to
   puzzle out the meaning of all of the pins on the cards.
   Hopefully the future evenings I spend on this will be as
   fun.