Stable Adc Reading Routine

[gebillpap]

Thank you for responding
I will try to describe the problem I face better in order to justify why I think that something like the stable ADC mentioned in my first post might solve it.
A 12f675 chip gets ADC readings of a battery undergoing charging with currents 0,1-4A.
The voltage is monitored and displayed every 1 second with resolution of two decimals (for example 8,17 V).
Since the battery is under charge it's voltage is climping up steadily and the display should show (at 1 sec rate ) voltages like 8,17 - 8,17 -8,17-some time -8,17 -8,17 -8,18 -8,18-some time-8,18- 8,19- some time-etc.
But what happens is that I get the voltage increase in "bursts" of three like 8,17 - 8,18 -8,19- 8,19 - 8,19 -8,19- some time-etc. every time there is a slight increase in voltage.
This is probably due to my manipulation of ADC data with adding 64 readings to achieve a 16 bit result and so on .
Í believe that with the stable adc routine ,mentioned in my first post, I can improve my display of voltages.

Anyway can anyone propose some picbasic equivelant for the stable ADC routine???

Bill

[Melanie]

OK Adam, you asked for it... here it is... quickly thrown together for an 18F2420... (you can probably optimise it with a bit of thought, but it's a starter just to get going)...

The variables...

	ADCValue var WORD			' Final ADC Result
	CounterA var BYTE			' Just a BYTE Temporary working variable
	DataW var WORD				' Just a WORD Temporary working variable
	RawData var WORD [16]			' Array holding ADC Result

Some Initialisation Set-up's for the PIC....

	ADCON1=%00001110			' ADC Control 1
						' 	7=0 - 0 Unused
						' 	6=0 - 0 Unused
						' 	5=0 - VRef=Vss
						' 	4=0 - VRef=Vdd
						' 	3=1 )
						' 	2=1 ) RA0 set to Analogue
						' 	1=1 ) All others set to Digital
						'	0=0 )
	ADCON2=%10101001			' ADC Control 2
						' 	7=1 - Right Justified - Read 10-Bits
						' 	6=0 - 0 Unused
						' 	5=1 )
						' 	4=0 ) TAD
						' 	3=1 )
						' 	2=0 )
						' 	1=0 ) Fosc/8
						'	0=1 )

Now for the real program... First TAKE your SAMPLES...

		'
		'	Stuff 16 Element WORD Array full of ADC values
		'	----------------------------------------------
	For CounterA=0 to 15
		ADCON0=%00000001		' Select Channel, Turn-On A/D
						'	7=0 Unused
						'	6=0 Unused
						'	5=0 )
						'	4=0 )
						'	3=0 ) selects AN0
						'	2=0 )
						'	1=0 Go-done Bit
						'	0=1 switch-On ADC Module
		Pauseus 50			' Wait for channel to setup
	        ADCON0.1 = 1			' Start conversion
		While ADCON0.1=1:Wend		' Wait for conversion
		DataW.HighByte=ADRESH		' Read variable from ADC and save
		DataW.LowByte=ADRESL
		RawData(CounterA)=DataW
		Next CounterA

Then SORT your RESULTS...

		'
		'	Sort ADC Input
		'	--------------
	CounterA=0
GetADCSortLoop:
	If RawData(CounterA+1) < RawData(CounterA) then
		DataW=RawData(CounterA)
		RawData(CounterA)=RawData(CounterA+1)
		RawData(CounterA+1)=DataW
		If CounterA>0 then CounterA=CounterA-2
		endif
	CounterA=CounterA+1
	If CounterA<15 then goto GetADCSortLoop

Finally EXTRACT SOMETHING USEFUL from what you've got...

	'
	'	Quanticise discarding top and bottom FOUR elements
	'	----------------------------------------------------
	DataW=0
	For CounterA=4 to 11
		DataW=DataW+RawData(CounterA)
		Next CounterA
	ADCValue=DataW>>3			' Divide Result by EIGHT

Ain't so difficult when you break it down into little steps is it?

[Pic_User]

Hi Melanie,

Thanks a bunch, this is really easy to understand.
You are spot on, it is overwhelming looking at the problem. Trying to get a foothold.
But not so bad step by step.

Of coarse it is easy with the code as an example.

I will study the whole thing. I learn, not just from your excellent example of how to code it. But, from the style of logic flow and layout. It is good, the way you comment lines of code that seem obvious to you but cause a noobe to pause and check. This allows us to get beyond the mechanics quickly, and see the part you are showing us.

I have saved this example and will try to learn and build from it. You’re the greatest!

(notice the "spot on", my co-workers have noticed my accent growing!)

-Adam-

[Melanie]

Of coarse it is easy ... my co-workers have noticed my accent growing!

You're getting there - but you're still a little coarse (of course!).

[Pic_User]

Thanks.

You're getting there - but you're still a little coarse (of course!).

Of course, embarrassed, I now wander off in search of the “misused words” forum…..
-Adam-

[gebillpap]

Dear All
I replaced my own routine for ADC readings with Melanie's just to see if there would be any difference in displayed voltages.
I found out that there was always an increase in steps of 30mV(remember that I display with a resolution of two decimal digits) instead of my previous output in short bursts of gradually increasing values by 10mV.
So I came to the conclusion that my problem lies with the resistive divider that I use in order to be able to read voltages up to 30V.This is division by 6 and with the 0,004887 V / step(due to 5V max./1023 for 12F675) we arrive at apx. 30mV / new step which is unavoidable.
I think that I have to use some OPamp method(differential) to read voltage without stepping down through a ressistive divider.
I would welcome any thoughts and/or suggestions on the subject.
I thank all of you and especially Melanie(for the exceptional/disciplined programming techniques she uses) for the time you dedicated for me.
Also please forgive any grammar mistakes I make since I am only a native Greek .

Bill

[Pic_User]

Dear All
I replaced my own routine for ADC readings with Melanie's just to see if there would be any difference in displayed voltages.
I found out that there was always an increase in steps of 30mV(remember that I display with a resolution of two decimal digits) instead of my previous output in short bursts of gradually increasing values by 10mV.
So I came to the conclusion that my problem lies with the resistive divider that I use in order to be able to read voltages up to 30V.This is division by 6 and with the 0,004887 V / step(due to 5V max./1023 for 12F675) we arrive at apx. 30mV / new step which is unavoidable.
I think that I have to use some OPamp method(differential) to read voltage without stepping down through a ressistive divider.
I would welcome any thoughts and/or suggestions on the subject.
I thank all of you and especially Melanie(for the exceptional/disciplined programming techniques she uses) for the time you dedicated for me.
Also please forgive any grammar mistakes I make since I am only a native Greek .

Bill

Hi Bill

Take a look at this post.
http://www.picbasic.co.uk/forum/showthread.php?t=8070

You will have to extrapolate the Voltage up from the 12 Volt example given. Hope it helps….

Melanie doesn’t really make fun of grammar. We have a running joke about the difference between REAL English and American English. She was just catching a goof of mine. Your English is better than mine!

-Adam-