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Summary:

  • I am using an Arduino UNO.
  • I am using a potentiometer connected from 5V Arduino supply to ground to provide a variable voltage on the pot wiper, which I input to an analog input on the UNO to allow variation of a PWM signal.
  • As I load the supply with peripherals the supply voltage droops from 5V to say 4.8V and this affects my PWM frequency.
  • How do I prevent supply voltage changes affecting my PWM settings?

Schematic 1

I'm working on a project, and since I have been adding things to it some new problems started to appear. Here is the diagram of the project:

Schematic 2

I'm using a potentiometer to control an output pin (PWM). As seen in the diagram, the potentiometer takes the 5 V as reference and sends back to the pin 2 the voltage so it can be taken by the ADC. The problem is that, with all the new connections, I have had a drop of voltage on VCC from 5 to 4.8 V, which kind of messes up with the selection of voltage. For example, if I want the pin 2 to be on 5 V, once I put the potentiometer on the max ammount of voltage it will just give me 4.8 V.

I just checked and putting everything off except the potentiometer solves the problem.

Should I use an external feeding for the LCD display?
Or should I use the 4.8 V as a parameter of reference?

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    \$\begingroup\$ People will close this if you do not clarify. What does the pot do? Why does it matter if it sees 4.8V. What ... ? || People also greatly dislike that sort of diagram as opposed to a "proper" circuit diagram. || You appear to have two pots. || If you care then feed the pots from a regulated supply supplied from 5V. \$\endgroup\$ Commented Nov 6 at 14:00
  • \$\begingroup\$ IF people close the question it can be reopened if you clarify things and then flag for eeopening. \$\endgroup\$ Commented Nov 6 at 14:00
  • \$\begingroup\$ Check the 5V without wiring the LCD Display. \$\endgroup\$ Commented Nov 6 at 16:09
  • \$\begingroup\$ @Vamir You use the phrase "using a potentiometer to select between 0 and 5 volts". I think what you mean by this is that you have the ends of the potentiometer connected to Ground to & +5V, and the wiper to one of the UNO's analog inputs. Or maybe to a voltage input of the LCD. You have to clarify exactly what you are intending to do here of you want meaningful help. Using the word "selection" is a bit odd when describing a pot, I think you really mean "adjust". \$\endgroup\$ Commented Nov 6 at 17:27
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    \$\begingroup\$ You could also help us help you if you remove the different parts (LCD, pots, motor (running/paused), fork light barrier) individually and cumulative and measure the supply voltage. Please edit your question to add the results. \$\endgroup\$ Commented Nov 7 at 15:49

1 Answer 1

Reset to default
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Added: thebusybee has pointed out that the UNO has a 3V3 output. This would be the even-easier way of supplying the potentiometer with 3V3.

Easiest solution is to operate the potentiometer from a lower regulated voltage that does not vary (much) when the 5V rail does.

Simplest and possibly good enough is a zener diode.

You do not say what the potentiometer value is.
Assuming a 10k pot, supply it with a say 3.3k resistor.
Vpot_top now should be 5V x 10k/(3.3k+10k) = 3.76 V.
Now connect a 3V3 zener from pot top to ground.
R_3k3 current will be I = V/R = (5-3.3)/3k3 = 0.5 mA I_pot will be i = V/R = 3.3/10k = 0.33 mA.
And I zener will be 0.5-0.33 = 0.17 mA.
This is "on the low side" for good regulation.
Maybe use a 1k instead of a 3K3.
Voltage should be stable enough for your purpose.
If not, a 3V3 voltage regulator to supply the pot will be somewhat more stable.

Note that 3V3 was chosen semi randomly.
But 3V3 zeners and voltage regulators are readily available and low cost.

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  • \$\begingroup\$ The UNO provides a power output of 3.3V already. \$\endgroup\$ Commented Nov 7 at 12:12
  • \$\begingroup\$ @thebusybee Thanks / Doh. Even easier. 3V3 was a VERY good choice :-) \$\endgroup\$ Commented Nov 7 at 14:39

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