Anti-log Pot track puzzler?

[pwdrive]

Hello David something has gone wrong somewhere, If a taper resistor is connected from the "top" end of a linear pot to i'ts slider then at the pots mid position you have an unequal voltage divider as opposed to an equal voltage divider if the taper resistor were not fitted as per Ohms Law
I am assuming that the taper resistor you tried was no more than one sixth the value of the linear pot concerned ie: 8.2k for a 50k pot.

Lawrence.

(Edit) General warning: If a pot fitted with a taper resistor is used in a DC circuit then this combination will be passing progessivly more current as it is turned towards it's minumum setting (reverse log) or at it's maximum setting (log)

[Yorkie]

Hi Lawrence.

Thanks for your coments.

I've tried to do this again, with the same results. I've attached a diagram showing how I set the 50k linear pot up, with an 8k2 resistor from the slider to the top of the pot. I then put an ohmmeter across the slider and bottom of the pot and tracked the results, which resulted in a perfectly linear line - not an anti-log curve. The line was below that of a 50k linear pot on its own, and the total resistance was 42 k - not 50k.

What I want it to behave like is a 50k antilog pot in the role shown as in the circuit diagram.

You could say that I've still lost the plot - no surpises there then!

Hope the crude diagram makes sense, even though the results seem not to.

[pwdrive]

Hello David, if you are measuring from the slider to the bottom of a linear pot (50k) and the taper resistor is of a fixed value (8.2k) then surely you must be plotting a linear function as the top of the pot is not referenced to anything, try plotting from the top of the pot at it's junction with the taper resistor and the bottom of the pot it should plot a non linear plot on the graph.

Lawrence.

[pwdrive]

Also as it's all to do with changing ratios then feed a safe voltage across the pot and measure the voltage on the slider as a function of voltage/rotation.

Lawrence.

[pwdrive]

This link is in bigger writing and maybe easier to understand.

http://gaussmarkov.net/wordpress/parts/r...rs-6-mods/

Lawrence.