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Campbell Lighting
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United States - Member - Donald here, Campbell Lighting Co. Engineering Fields - Retired Engineers / Mentors - New Member

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Location: central arkansas
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Analog to Digital

12/20/2007 1:48 PM

Hello all you Brilliant Minded People,

I envy anyone who has the patience to figure out these details in low voltage design...

I have more patience with High Voltage, than Low Voltage, (at least I know what the result of high voltage will do).

Anyway, now to the problem, and question:

We have a simple electric/electronic PCB, basically single side, with the exception of a single 3-position toggle switch on the back side.

This board is an incandescent dimmer, using common Triac design.

Because my EE has been called back to the Iraq war, I am forced to figure this out myself, (Which I feel very lacking in experience, and patience).

We are attempting to convert basically an analog Potentiometer, so that we can still use the pot, but also have a digital LED readout to display the setting of the pot into characters from 0-99.

My apprentice friend used his Radio Shack Kit and came up with a board that almost accomplishes this goal.

Our problem is, as we turn the pots knob, the separation between the numbers is SO close, that it's hard to keep it on one display number, so flickering between numbers is the distracting problem. We can make it stop, but you have to be exact...

My question is:

How can we still use this rotary POT, but make the board with a little more separation between the numbers so as to avoid that annoying flicker if you don't get it set just perfect.

I know we could avoid all of this by just switching over to to normal push type digital, and we may have to do this eventually, but then our design must change and much more is involved..

Please guys, in the Spirit of Christmas, is there any way we can remedy this, using our old design with the manual POT ?

Sincerely,

Frustrated in Arkansas,

Donald

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bhankiii
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#1

Re: Analog to Digital

12/20/2007 2:20 PM

The problem is one of resolution. You're trying to divide 120 degrees (or so) of rotation into 100 discrete pieces.

Possible solutions:

Only display the 10's digit - so you have 0-9 instead of 0-99.

The problem could also be noise - if the noise on your signal is greater than your full range voltage divided by 100, then your noise is greater than your delta value. You might try a simple lowpass filter (series resistor with a capacitor to ground) on the line going into your digital thingy. Or add some hysteresis. I'm not sure how to do this since I don't know what circuit you have.

But seriously, I'd drop the lower digit.
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user-deleted-1105
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#2

Re: Analog to Digital

12/20/2007 3:04 PM

Use a multi-turn pot!

Simple but effective...that'll be £5 please

Del

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FKIA
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#9
In reply to #2

Re: Analog to Digital

12/21/2007 10:57 AM

Dell has the most cost effective answer. And, the low pass filter should be part of the design anyway. Both are very inexpensive and effective. Well, that's my 2 cents for what it's worth.

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Toptekkie
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#3

Re: Analog to Digital

12/20/2007 3:08 PM

Analog to digital.

Use a microcontroller to 'measure' the analog value digitally and in firmware apply hysteresis by requiring the value to change more than 'x' bits before changing the display.

http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en025234

Above is a good idea of how to smart dim using an IR remote which could be adapted to measure the setting of a pot.

To measure the setting of the pot you can then use two IO pins on a PIC with a capacitor charged by the POT from an IO PIN when logic hi and discharged through the IO PIN when lo. Simply count the time to sense a change of state on the second input pin.

If this needs more info and details then look at the Microchip website for typical applications.

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Anonymous Hero
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#4

Re: Analog to Digital

12/20/2007 8:00 PM

You can try not using some of the lower bits of the output of the Analog to Digital converter. This will reduce the resolution and hide the noise you experience.
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JohnDG
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#5

Re: Analog to Digital

12/20/2007 8:32 PM

I suspect you're suffering from noise/jitter or whatever on the display circuit input.

Put a decent sized resistor in series with the display cct input, and a capacitor in parallel after that (on the display side). Assuming the display cct has a high impedence input, 100K and 1μF should do the trick.

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Campbell Lighting
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United States - Member - Donald here, Campbell Lighting Co. Engineering Fields - Retired Engineers / Mentors - New Member

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#6
In reply to #5

Re: Analog to Digital

12/21/2007 12:11 AM

Boy, guys, that was quick, and VERY informative, and I REALLY appreciate it for sure..

This forum is SO GREAT, I enjoy being on it tremendously!

Merry Christmas, and Happy New year, to all of you!!

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#7

Re: Analog to Digital

12/21/2007 5:40 AM

so what is that pay scale for work performed
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Electroman
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#8

Re: Analog to Digital

12/21/2007 9:17 AM

As the light level to the human eye is roughly logarithmic, don't those dimming controller pots use a log law track?

In which case I can't see how you would use the track position as anything other than a rough idea of light output.

So why do you need the precision? As the posters have said surely a 0 to 9 display would be more than adequate?

John.

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Campbell Lighting
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United States - Member - Donald here, Campbell Lighting Co. Engineering Fields - Retired Engineers / Mentors - New Member

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Location: central arkansas
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#10
In reply to #8

Re: Analog to Digital

12/22/2007 7:18 PM

Yes It would, and we will change that accordingly..

Thanks for all the input.

Donald

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Anonymous Hero (1); Anonymous Poster (1); bhankiii (1); Campbell Lighting (2); Electroman (1); FKIA (1); JohnDG (1); Toptekkie (1); user-deleted-1105 (1)

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