Re: Risetime calculator (in tekwiki)

Albert Otten

On Sun, Jan 19, 2020 at 09:07 PM, Leo Bodnar wrote:

It's not intuitive but if you do the math it is, indeed works out perfectly
linear - assuming the trim pots are set to the value of 50R.
Whoever designed it, deserves to be an employee of the month.
These days such a gadget would have at least some duino inside it.
On Sun, Jan 19, 2020 at 05:28 PM, Albert Otten wrote:
Actually the math appears to be surprisingly simple and in theory the
instrument shows EXACT results with LINEAR pots..
This originates I think from the idea that around a maximum or minimum a function is quadratic plus higher order terms.
If you short together both ends of a linear pot then the resistance to the wiper is maximum midway and decreases quadratically (in this case exact, without higher order terms) when moving away from midway. In our instrument consider a wiper as a wiper of a 10 k pot, blocked midway in one direction.
I must confess that I only recognized the trick after further investigation.


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