Potentiometer + fixed resistor law

[StephenGiles]

Has anyone come accross a website providing an alternative pot law finder? For instance circuit requires 250k log with 1meg fixed resistor accross wiper to outer terminal - what value resistor would be required with 470k log to produce similar law??

[R.G.]

Unfortunately, the necessary requirement is math.

I did all the graphs on "The Secret Life of Pots" from writing out the voltage divider equation for a pot with a resistor from CW terminal to wiper and another from CCW terminal to wiper. I called the CW to wiper resistor Rtop ad the CCW to wiper Rbot. I split the pot into resistance above the wiper and below the wiper, and called the "bottom" part of the pot Rpot*(alpha), the top part of the pot Rpot*(1-alpha) where alpha is the percentage of rotation, going from 0 to 1. I then wrote the equations for the wiper voltage in terms of these resistances. With that equation, I could call Rtop beta*Rpot and Rbot gamma*Rpot, and have an equation with only alpha (the rotation), beta (the relation of Rtop to Rpot) and gamma (the relation of Rbot to Rpot) and Rpot itself, which I called "one". Setting beta and gamma to some values between just zero and infinity and using alpha as an independent variable gave the plots. In most cases I set beta or gamma to very, very high; this made Rtop or Rbot be substantially infinite.

After that, plug the equation into a spreadsheet and tell it to plot the results for alpha between 0 and 1 in whatever steps I liked.

Quite a lot of an engineering undergraduate education consists of either learning to do that process, or using it as a presumed basic skill.

[StephenGiles]

Thanks RG..........it's trial and error then for me I gave up maths in 1964 when I left school!!

ah and I've been a humble accountant ever since - don't need maths for that!!

[tubegeek]

Quite a lot of an engineering undergraduate education consists of either learning to do that process, or using it as a presumed basic skill.

Other than this, the rest consists of fashion tips.

[GibsonGM]

Quite a lot of an engineering undergraduate education consists of either learning to do that process, or using it as a presumed basic skill.

Other than this, the rest consists of fashion tips.

..and learning how to write in that ubiquitous neat script...