Reading Six Potentiometer at the same time? (Panda)

NETMF & Gadgeteer
1

I’m working on a project that need to read values from six 10K potentiometer sliders,
that connected to analog pins, An0 - An5 (See images for schematic.)

Everything seem to work well. But one thing that I am not happy with it is that
whenever I slide one of the sliders up and down (I set the scale for all the sliders between 0-255).
All the other sliders seem to increase/decrease the value as well.(see the debug result on the image.)
The values seem to be in the ~10% range of the one that is used.

This is probably a noise among the analog pins (An0 - An5)???
My question is that if there are any way to get ride of these noise?
And how, any suggestion?

Here si the code that I use to measure the values of the sliders:


using System;
using System.Threading;

using Microsoft.SPOT;
using Microsoft.SPOT.Hardware;

using GHIElectronics.NETMF.FEZ;

using GHIElectronics.NETMF.Hardware;

namespace FEZ_Panda_Application1
{
    public class Program
    {
        const int avgCount = 6;

        // Slider Potentiometers
        //Color, Saturation, Bright, Transparent, Width, Fade;
        static AnalogIn colorSlider       = new AnalogIn((AnalogIn.Pin)FEZ_Pin.AnalogIn.An0);
        static AnalogIn saturateSlider    = new AnalogIn((AnalogIn.Pin)FEZ_Pin.AnalogIn.An1);
        static AnalogIn brightSlider      = new AnalogIn((AnalogIn.Pin)FEZ_Pin.AnalogIn.An2);
        static AnalogIn transparentSlider = new AnalogIn((AnalogIn.Pin)FEZ_Pin.AnalogIn.An3);
        static AnalogIn widthSlider       = new AnalogIn((AnalogIn.Pin)FEZ_Pin.AnalogIn.An4);
        static AnalogIn fadeSlider        = new AnalogIn((AnalogIn.Pin)FEZ_Pin.AnalogIn.An5);

        static int colorValue, saturationValue, brightValue, transparentValue, widthValue, fadeValue;

        static int[] colorAvg       = new int[avgCount];
        static int[] saturationAvg  = new int[avgCount];
        static int[] brightAvg      = new int[avgCount];
        static int[] transparentAvg = new int[avgCount];
        static int[] widthAvg       = new int[avgCount];
        static int[] fadeAvg        = new int[avgCount];

        //Button
        static bool buttonState;

        static InputPort Button = new InputPort((Cpu.Pin)FEZ_Pin.Digital.Di7, true,
                                                Port.ResistorMode.PullUp);
        public static void Main()
        {
            int index = 0;
            colorSlider.SetLinearScale(0, 256);
            saturateSlider.SetLinearScale(0, 256);
            brightSlider.SetLinearScale(0, 256);
            transparentSlider.SetLinearScale(0, 256);
            widthSlider.SetLinearScale(0, 256);
            fadeSlider.SetLinearScale(0, 256);

            //reset sliders average
            for (int i = 0; i < avgCount; i++)
            {
                colorAvg[i] = 0;
                saturationAvg[i] = 0;
                brightAvg[i] = 0;
                transparentAvg[i] = 0;
                widthAvg[i] = 0;
                fadeAvg[i] = 0;
            }

            while (true)
            {
                //Read button
                buttonState = Button.Read();

                //calc average value
                colorAvg[index]       = colorSlider.Read();
                saturationAvg[index]  = saturateSlider.Read();
                brightAvg[index]      = brightSlider.Read();
                transparentAvg[index] = transparentSlider.Read();
                widthAvg[index]       = widthSlider.Read();
                fadeAvg[index]        = fadeSlider.Read();

                // increment index, if index > array size reset to zero
                index++;
                if (index >= avgCount)
                    index = 0;

                // calc sliders average value
                slidersAverage();

                Thread.Sleep(10);

                //Display the sliders' value
                Debug.Print("Sliders: " +
                    (colorValue).ToString() + "\t" + (saturationValue).ToString() + "\t" +
                    (brightValue).ToString() + "\t" + (transparentValue).ToString() + "\t" +
                    (widthValue).ToString() + "\t" + (fadeValue).ToString());

                Debug.Print("Button: " + buttonState.ToString());
            }
        }

        public static void slidersAverage()
        {
            colorValue = 0;
            saturationValue = 0;
            brightValue = 0;
            transparentValue = 0;
            widthValue = 0;
            fadeValue = 0;

            for (int i = 0; i < avgCount; i++)
            {
                colorValue += colorAvg[i];
                saturationValue += saturationAvg[i];
                brightValue += brightAvg[i];
                transparentValue += transparentAvg[i];
                widthValue += widthAvg[i];
                fadeValue += fadeAvg[i];
            }

            colorValue       /= avgCount;
            saturationValue  /= avgCount;
            brightValue      /= avgCount;
            transparentValue /= avgCount;
            widthValue       /= avgCount;
            fadeValue        /= avgCount;
        }
    }
}
2

I wonder if using 1K pull down resistors on analog pings will help. Try that.

Also, check this:

3

Looks like when the slider is low you’re sending 5V into the analogin. What happens when you bias the pot array with 3v3?

4

Or if you really want to use 5v connect aref pin to 5v as well?

5

WhysItSmoking:

That’s solve the problem! ;D

Thanks to you too, Architect.

6

Yes, you can’t exceed 3.3V on analog inputs

7

cool. glad it’s working Sam.

@ architect – the AREF pin from arduino pinout is NC on panda. AREF is hard wired to 3v3 at the chip. I’ve briefly considered doing surgery to “fix” that…

8

Did you think of why GHI didn’t leave vref on the pins, so you can connect it to 5V? :slight_smile:

It is because 5V on vref will damage the processor and this is why GHI didn’t connect it :wink:

9

This project is an old project that I am replacing the Arduino with Panda.
And the connections was on 5V.
I totally forget about this 3.3V, as it was mentioned in the eBook.
:-[

10

[quote]5V on vref will damage the processor[/quote] ouch! :o

Just read chapter 27 section 5 of the user manual.

Good to know! Thanks

11

I forgot this too lately. Luckily the GHI/tinyclr boards are so robust 8)

12

@ Gus, I was contemplating “surgery” to allow me to supply <3v3 to the chip’s vref. Trying to get better ADC resolution at low voltage levels.