TI-66 double speed mod

[ijabbott]

(07-12-2022 09:29 PM)John Garza (3665) Wrote:  

(07-11-2022 04:15 PM)Nigel (UK) Wrote:  For those who are interested, the attached graph shows how the calculator speed varies with resistance.


It would seem to be sensible to choose a resistor value that lies well away from the jump, or from the final failure point. There's no guarantee that the step up will be at the same point on all calculators, or that it will stay fixed as conditions change. In my initial experimentation I found that a 22k resistor in parallel with the 180k resistor wouldn't work; this time it did, and the failure occurs for resistances less than about 18k. This is quite a drift! (The weather is hot today.)

Nigel (UK)

Great work on the chart Nigel !
So... maybe a 20K in parallel ?
-J

Sticking with E24 series resistor values:

20K in parallel with 180K would give 18K total.
22K in parallel with 180K would give 19.6K total.
24K in parallel with 180K would give 21.2K total.

Maybe go with the middle one (22K) first? (22K has the slight advantage of being an E12 series value.)