How to alter a analog signal

Other Hardware General Electronics
1

HI , im after a way to alter the output of a potentiometer and this to be controlled by the arduino .
I have a potentiometer that is being used as a position sensor it normally reads between 1 and 4 v , When activated by the arduino i want the output of this to be altered to 3.5v if this is higher than the pots own value , ( the higher value will always be the one output ) . This seemed easy to me at first and tried a second pot in parallel switching the signal wire but i then realised the 2 voltage dividers will interact with each other and when the 3.5 v applied if the position sensor goes to its 4 v position the output will be well over 4v .
I think i can figure out some ways to do this using the analog write and a filter but id like to know how this can be done with just components so than when the arduino put out the 5v high the components sort out the rest .

Any help appreciated , Thanks

2

I have a hard time following your request.

you are using a a pot as a position sensor.
typical output is 1 - 4 volts

for some un-known reason the arduino if activated and outputs a 3.5v signal.

the higher signal will pass.

========================

send you 1-4 into your arduino. on an analog pin
then send it out on a PWM pin.
software would look for that un-known reason to activate and once activated, the output would be 3.5 minimum or it would output the actual input if that is greater than 3.5v

if you wanted discrete components, you could use an op-amp.

3

simon100:
HI , im after a way to alter the output of a potentiometer and this to be controlled by the arduino .
I have a potentiometer that is being used as a position sensor it normally reads between 1 and 4 v , When activated by the arduino

How is your Arduino 'activating' a pot?

i want the output of this to be altered to 3.5v

The output of what? If you mean the pot, use a fixed resistor in series with it. If you had told us the value of the pot, we could have told you the value of resistor to use.

if this is higher than the pots own value , ( the higher value will always be the one output ) . This seemed easy to me at first and tried a second pot in parallel switching the signal wire but i then realised the 2 voltage dividers will interact with each other and when the 3.5 v applied if the position sensor goes to its 4 v position the output will be well over 4v .
I think i can figure out some ways to do this using the analog write and a filter but id like to know how this can be done with just components so than when the arduino put out the 5v high the components sort out the rest .

None of that made any sense. A diagram may have helped.

4

You need a robot arm to twiddle the knob attached to the pot. That is what you seem to be asking for.

5

Perhaps you need something like this

float pot_volts = 5.0*analogRead(A0) /1023.0  ;                             // or 1024.0  if you prefer.
float output_volts = ( pot_volts > 3.5 ) ? (pot_volts) : (3.5)  ;    // output volts will be the larger of pot_volts or 3.5
float output_countf = 255.0*output_volts/5.0 ;
int output_count = (int) output_countf ;
analogWrite( output_count );

And then you need some suitable hardware ( capacitor circuit ) to smooth the resulting PWM output to a constant DC voltage.

6

Sorry im bad at explaining things .

1 , i have a device that uses a potentiometer as a position sensor .
2 , The arduino should not be used except to provide a on off signal to this module i want to create
3, This module when activated will alter the signal from the potentiometer to be 3.5 .
4, The position sensor has a output range from 1-4 v during operation .
5 , When the module is activated the total output much never exceed 4v
6, The potentiometer has a 5v supply and this cannot be changed

7

What is the device? I suspect the xyproblem here: http://xyproblem.info/

8

Theres no x y im really asking the question i asked , i don't want a solution to the problem im sure there is many ways to do it using the arduino but i was trying to do it with a simple circuit and couldn't work it out but i'm sure there is a way . Something with some transistors , diodes and resistors .

9

So can we assume you cannot disconnect this pot? In which case you're
limited to using an opamp in voltage-follower mode to drive the wiper - this
would overload if the wiper was at the end of the track, but most opamps
overload safely with low current limits, and in the mid-travel the opamp
feedback would dominate the effect of the pot and control the voltage stably.

10

Theres no x y im really asking the question i asked

As you say you are not good at explaining things.

This module when activated will alter the signal from the potentiometer to be 3.5 .

So is that the output of the wiper will change from the variable it normally is to 3.5V?

If so then a simple analogue switch should do it something like a 4051, 5052 or 4053. One input goes to the wiper, the other to a fixed 3V5 generated by a potential divider and the output to where ever it needs to go.
Then the arduino can control the multiplex pin to select one or other inputs.