Software ADC Comparator?

[Ryan7777]

the first suggestion by mackrackit doesn't take into account the level of "difference"
i.e. setting the output high based on the amount of change of a varible number, not just by the fact that it changed for one.
and its classified skimask! but, heres an example:

say my input is a light dependent resistor, or solar cell, whatever, and its sitting in a dark room, doing nothing, no output. then someone turns on a dim light, the pic would detect the change in light level in the span of one loop, and toggle an output on and off one time because it saw a positve change in voltage on the ADC.
Then it readjusts for the new light level in the room and sits there, doing nothing, but someone makes the light a bit brighter, and again the output toggles because there is a positve change in light. so therefore, it only toggles the output because there is a positve change in light, it would ignore someone turning the light off, or dimming it. I also need control of how much of a positive change it responds to, like the amount that the voltage level is increased, so if its a very slight change, nothing happens, but if there is a large change, it will respond..
this is really messing with my poor ol' brain! but i seem to end up asking more questions on here than answering anyway!

Also, when i say "readjusts" i mean the circuit automatically readjusts its self, like autogain, or something!

thanks again for your help!

[skimask]

and its classified skimask! but, heres an example:

I've seen classified (or have I?)...this isn't classified (or is it?)...

say my input is a light dependent resistor, or solar cell, whatever, and its sitting in a dark room, doing nothing, no output. then someone turns on a dim light, the pic would detect the change in light level in the span of one loop, and toggle an output on and off one time because it saw a positve change in voltage on the ADC. Then it readjusts for the new light level in the room and sits there, doing nothing, but someone makes the light a bit brighter, and again the output toggles because there is a positve change in light. so therefore, it only toggles the output because there is a positve change in light, it would ignore someone turning the light off, or dimming it. I also need control of how much of a positive change it responds to, like the amount that the voltage level is increased, so if its a very slight change, nothing happens, but if there is a large change, it will respond..
this is really messing with my poor ol' brain! but i seem to end up asking more questions on here than answering anyway!
Also, when i say "readjusts" i mean the circuit automatically readjusts its self, like autogain, or something!

If you read thru what you wrote carefully enough...you've just wrote the program that you want....no, really. I was writing it as I was reading it.
Now my question is, the input can only go so high. Once it gets up to a maximum value, what's going to bring it back down to a nominal nothing?

[Jerson]

Ryan

What you're looking for is a derivative function. What you can do is something like this

LastADC  var   word    ' previous error
CurrADC  var   word    ' current error
Threshold con  1        ' can be more if you want

loop:
  gosub ReadADC
  Error = CurrADC-LastADC
  if Error < 0 then Error = -Error ' make absolute error
  if Error > Threshold then
    High Output
    pause 1000    ' wait 1 second
    Low Output
  endif
  LastAdc = CurrAdc
  goto loop

This will more or less achieve what you want to. However, this is pure untested code. Use at your own risk.

Jerson

[Ryan7777]

I tired your code, Jerson, and it didn't seem to work right, say the ADC had 2.5 volts applied, and then i turned the voltage up to 3 volts, the output would turn on and off, over and over, rather than toggle once, to show a change happened, and then stop. i changed the threshold value to account for any instabilty in my input voltage, and still no dice. and like a i said before, i need the circuit to "readjust automatically" so that it only cares that there is a positive increase in voltage by a certain value and reacts once and then resets, it shouldn't care what the original ADC value was, only that the value increased. so it would have to "dynamically" adjust itself. you would figure that you would take a reading, and then some miliseconds later, take another reading, subtract the first value from the second and that number would show a difference (if there is any), which would mean a positive change. if that value was over that of the threshold, then react. you would have to clamp that value to a number between 0 and 1023, so there wouldn't be a negative value and a roll over (or under, in this case) which i think is what Jerson's code showed, and i already tried the same thing, in a slightly different way, and neither work... but i could be, and probably am missing something! i really don't understand absolute values (only their vodka!) and how it applies here, all your saying is that the number can only have a certain maximum value right? so couldn't i use MAX?

[mackrackit]

Like skimask said, you have the code in you explanation of the project.
Jerson gave an "untested" example to get you started.

Think about this:

Two VAR : read ADC first : write that value to VAR1 : start LOOP : read ADC :_
write ADC value to VAR2 : IF VAR2 > VAR1 THEN ? : Now make VAR1 = VAR2_
GOTO LOOP

[Ryan7777]

This is what i got so far, and im not seeing why it doesn't work.
please excuse the formatting and what not!

@ DEVICE pic16F684, HS_OSC, WDT_OFF, PWRT_OFF, MCLR_ON, BOD_OFF, IESO_OFF, FCMEN_OFF

DEFINE OSC 20
DEFINE ADC_BITS 10
DEFINE ADC_CLOCK 2
DEFINE ADC_SAMPLEUS 11

CMCON0 = %00000111
VRCON = %00000000

ANSEL = %00110100

ADCON0.6 = 0
ADCON0.7 = 0

voltLevBf VAR WORD
voltLevAf VAR WORD
voltLevCk VAR WORD
threshHold VAR WORD
timOut VAR WORD

prgSel VAR PORTC.2
swtOut VAR PORTC.3

CLEAR

PAUSE 1000


autoGainPrg:

ADCIN 2, voltLevBf

PAUSEUS 12

ADCIN 4, threshHold

PAUSEUS 12

ADCIN 2, voltLevAf

PAUSEUS 12

voltLevCk = voltLevAf - voltLevBf

IF voltLevCk > threshHold THEN

HIGH swtOut

PAUSE 60

LOW swtOut

ADCIN 5, timOut

PAUSEUS 12

PAUSE timOut

ENDIF

GOTO autoGainPrg:

the ADC acts as if there are two seperate voltage values present at the pin even if the voltage is the same and doesnt change. like on the first reading it should read 3 volts, and the second reading should be 3 volts or close enough! it shouldn't flash the LED sitting on the output, but its does, over and over like a blinky circuit, like the two readings are never close to equal, no matter what threshold is set at! so that would make me think that the difference between the two readings is somehow always larger than threshold.. what i'd like to know is, what did Jerson mean by "if Error < 0 then Error = -Error ' make absolute error" ?

IF Error < 0 THEN
Error = Error - Error
ENDIF
??? if so, i tried that version of it, and it didn't work either..

[Jerson]

Ryan

You seem to be reading 3 diff adc ports. First of all, you have to tell us what is each one for any of the code I gave to make sense.

The code I gave wants only 1 adc port to sense the light intensity. So, the other 2 are redundant. And the code I gave should do exactly what you asked for.

Check your code. You seem to have got it diff from what I have given you.

in Pseudo code what I have sent you does this

if CurrentADC != PreviousADC
Output = high
Wait 1 second
Output = Low
PreviousADC = CurrentADC
endif

Jerson