# Pots in parallel

Hello,

Could someone please help a noob like me understand the implications of having the 10MΩ resistor in the circuit i have uploaded. So far I've gathered it doesn't really influence the total resistance.
I thought it could decrease the current but adding a branch should slightly increase it since it add to the number multiplying the voltage in the formula..
And it doesn't help the pots handling the current when they go down in resistance, does it?

Thanks a lot,

antoine

#### Attachments

• Potentiometers in Parallel.jpg
13.7 KB · Views: 913

berkeman
Mentor
Hello,

Could someone please help a noob like me understand the implications of having the 10MΩ resistor in the circuit i have uploaded. So far I've gathered it doesn't really influence the total resistance.
I thought it could decrease the current but adding a branch should slightly increase it since it add to the number multiplying the voltage in the formula..
And it doesn't help the pots handling the current when they go down in resistance, does it?

Thanks a lot,

antoine

Welcome to the PF.

What is that circuit from? It would appear to do nothing, except maybe to set voltages between 5V and ground on the "Analog Input" signals....?

Hi berkeman,

The voltage across the pots is read by the analogue inputs of an Arduino Mega2560 (using the Atmel Atmega2560) programmed to send MIDI messages.

Thanks

antoine

berkeman
Mentor
Hi berkeman,

The voltage across the pots is read by the analogue inputs of an Arduino Mega2560 (using the Atmel Atmega2560) programmed to send MIDI messages.

Thanks

antoine

Ah, then yes, the 10M resistor does nothing.

As a side note, there should be some resistance either in series with each pot individually, or a resistor between one of the power rails and the rest of the pots.

This would keep the power rails from seeing a short if all Pots are turned to 0.

berkeman
Mentor
As a side note, there should be some resistance either in series with each pot individually, or a resistor between one of the power rails and the rest of the pots.

This would keep the power rails from seeing a short if all Pots are turned to 0.

That's not the way I interpret the diagram. It looks like the rails will always see the parallel combination of the full pot resistances, and the wipers just select up and down between the rails. The wipers are varying their output voltages, not varying any resistances, I believe.

jim hardy
Gold Member
Dearly Missed
that schematic raises more questions than it answers.

first question is are those variable resistors potentiometers or rheostats?

the arrow through element infers rheostats, which are just variable resistors

but both ends of element are shown connected as in a potentiometer where wiper taps voltage partway through element
and a rheostat is usually drawn with one end unconnected.

i suspect the arrow should be perpendicular to element and end where arrowhead touches element, as in a potentiometer

else the circuit makes no sense. Setting one variable resistor to zero would make all seven AN's read zero.

I call that sloppy draftsmanship.

if indeed they are potentiometers,,,
i notice they're located at various wheels and knobs.

Perhaps there's a connector and wiring harness involved?
then the 10meg could provide a minimum load for 5V line provided it remains in circuit when that connector is unplugged.

the picture is incomplete. my diagnosis is lazy drafting.

EDIT oops i see Berkeman got there already.

Berkeman, you are correct (no surprise there) - I see it drawn that way as well. I guess I shouldn't post early in the morning :-/

berkeman
Mentor
Yes, although I think jim hardy brings up good points about the ambiguities in the schematic as drawn.

Since it's an Arduino schematic, which is an Italian company (if memory serves me), perhaps that's just the European convention for a pot.

Just like, for resistors, they use a box and we use a squiggly.