Re: 7854 RAM card upgrade only - any interest?


 

On 11 Mar 2016 13:20:45 -0800, you wrote:

The dongle approach would add the cost of two connectors and a housing, Also all of the cable wires would have to be connected through (another circuit board or a wire and soldering iron session).
I was thinking that the dongle could be used instead of the external
keyboard.

The snap off printed board adds to the area ($) and would have to be the full height of the memory board, I guess, which is too big and it would have to snap in two to discard the excess area.
It would probably not be worth the extra cost given the simplicity of
the circuit. See below.

I tried to open my keyboard and ran into a problem with one screw that is so badly jammed that I may have to drill it out and replace it. Maybe inside the keyboard is not so easy after all.
I had the same problem with the keyboard and used a small socket
wrench with a T10 Torx bit to force the screws out. If it does not
turn, force it. If it breaks, it was defective anyway.

All of these seem like overkill to install just three components. If buyers will be doing all of their own mounting and soldering of sockets and components on the memory card, a tiny piece of perfboard with copper around the holes is a very common prototyping item for less than a dollar. We could just add that to the kit with instructions. All options will require some soldering somewhere, so no one solution has the advantage there, unless we provide a fully preassembled dongle based version at considerable extra cost.
I tested the single transistor open collector inverter wired onto a D
connector and it worked fine. The 7854 booted up in memory backup
mode instead of memory test mode when the dongle was attached to the D
connector in place of the external keyboard. I will make some
measurements of the signal voltages to verify good noise margin.
Adding a base-emitter shunt resistor might be necessary.

I had not really taken notice before but in self test mode, the 7854
beeps and displays the self test message. In memory backup mode, the
7854 displays the self test message without beeping.

Also in memory backup mode not only is the state of the vertical and
horizontal mode switches maintained, but so is the CRT mode of scope,
stored, or both. Tektronix thought of everything. I wonder if any
state *isn't* retained.

The rear A32 area may be the easiest to access after all.There is room in there to stick on a small pefboard using double faced foam tape, or the board might be soldered directly on the terminals of the new switch. Getting the three ribbon cables correctly replugged to A32 does take good light and a bit of dexterity.

Cliff
I would air wire it to the existing A32 rear panel connector board.

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