There is no sure fire way to solve this problem with a pot. This is because
there will always be a point where you are on the hairy edge of the ADC
switching and the smallest disturbance (i.e.: noise) will push you over the
edge.

The best you can do is to implement some hysteresis.

In other words you switch the value on the LEDs from N to N+1 when you see
ADRESHL go from N*16 to N*16+1.
However, to go in the other direction you wait for ADRESHL to go all the way
down to N*16-1 before switching back to N on the LEDs.

This can be implemented as follows:

forever:
    NewADRESH = ADRESH

    if NewADRESH > PrevADRESH then
        LEDS = NewADRESH >> 4;
    else
        LEDS = (NewADRESH + 1) >> 4;
    endif

    PrevADRESH = NewADRESH
end forever loop

Bob Ammerman
RAm Systems


leds to ge r
----- Original Message -----
From: "Spehro Pefhany" <speff@INTERLOG.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Saturday, July 26, 2003 9:45 PM
Subject: Re: [PIC]: ADC, Pot, need help


> At 09:33 PM 7/26/2003 -0400, you wrote:
> >Here's the setup: PIC16F872's ADC pin, PORTA pin 0, connected to a 1 Meg
> >Ohm pot. Four LEDs provide output.
> >
> >Here's the requirement: use the pot to select one of 16 values, 0 to 15
> >with the output being the 4 leds...a 4 digit binary number. All i do is
> >shift the 8 most significant bits (from the ADRESH, left aligned so 8
most
> >sig are in adresh with the two least sig in ADRESL) right four times so i
> >keep the four most significant digits which i directly output to the
LEDs.
> >
> >Here's the problem: when the pot is directly between two numbers, and
left
> >untouched, the pic will flicker between the two values because the pot i
> >suppose doesn't give a steady output. This isn't allowed. I've tried
> >adding a "debounce" where i wait to see if a value is held for 10 or 20
> >times before switching the display, but all it seems to do is slow the
> >flicker down. Any experience or suggestions? Thanks everyone... you have
> >no idea how much this community has helped me.
>
> Switch the pot for a lower value one (40K maximum, so maybe a 20K pot).
>
> 10K is the maximum input impedance.
>
> Best regards,
>
> Spehro Pefhany --"it's the network..."            "The Journey is the
reward"
> speff@interlog.com             Info for manufacturers:
http://www.trexon.com
> Embedded software/hardware/analog  Info for designers:
http://www.speff.com
>
> --
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>

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