Re: Temporary central repository of Darrel Taylor's works (including Mr E's Multicalc
DT_Analog
From Darrel's website . . . all his words, not mine.
You've probably noticed that when using the Analog to Digital converter, the numbers are NEVER stable. At best, the result will always be bouncing back and forth between two numbers.
While it's extremely annoying, there is a reason for it, and the number of times it bounces between those two numbers is actually indicating the values of more bits of resolution that are not included in the original 10-bit result.
This effect can be exploited to increase the effective number of bits in the result.
By taking a number of consecutive samples and averaging the results with a lower divisor, you can get up to 16-bit accuracy from that poor little 10-bit converter.
An explanation of the Oversampling technique can be found on Wikipedia.
http://en.wikipedia.org/wiki/Oversampling
A/D Bits Samples Required MAX result Conv. Time (1) 10 1 1023 24.2us 11 4 2046 96.8us 12 16 4092 387us 13 64 8184 1.54ms 14 256 16368 6.2ms 15 1024 32736 24.7ms 16 4096 65472 99.1ms Samples required:
(1) Conversion Time based on 5 us acquisition with 1.6 us Tad
For each additional bit of resolution, the number of samples required is multiplied times 4 (22(n-10)). The samples are accumulated in a 32-bit variable, then divided by a number that is doubled for each additional bit (2(n-10)). [This is all handled by the module.]
Maximum results:
Since the highest value provided by the converter is 1023, it can't bounce between 1023-1024.
This limits the maximum values to slightly lower than expected, which is (1023 << (bits-10))
For 16-bits, the maximum is (1023 << 6) or 65472. This value is returned in the ADmax variable after the conversion for easy voltage calculations.
Practicality:
Taking 1/10th of a second to convert a 16-bit value seems like a colossal waste of time. But it's nice to know you can do it if you really need to.
To me, the real winner is 12-bit, at under 400us conversion time, with a 4 fold increase in resolution, on almost any PIC, ... I doubt I'll be using 10-bit much anymore. But even 14-bit's not too bad @6ms, although the extra time for 14-bit probably isn't worth it for most analog projects.
Conversion time:
The time it takes to complete a conversion depends on a couple of factors.
1. The Acquisition time specified in the DEFINE ADC_SAMPLEUS statement. If there is no DEFINE, PBP will default to 50us, which is for the absolute worst case scenario with high impedance. It's very likely that you will be able to use a much smaller value. With an impedance of 1K or less, you can usually get away with 3-5us. Also, the minimum ADC_SAMPLEUS is limited to the minimum PAUSEUS delay, which at 4Mhz OSC is 24us, @20Mhz it's 3us. Use as low a value as you can possibly get away with because this time happens for every sample. With 256 or more samples being taken, it adds up pretty quick.
2. The ADC clock source should be set as close as possible to 1.6us Tad. And it takes 12 Tad to complete a 10-bit conversion. This one's hard to explain, so I'll just list the recommended values. Use the highlighted values in your DEFINE ADC_CLOCK statement, based on your oscillator frequency.
OSC DEFINE ADC_CLOCK Clk source Tad(us) 12 Tad(us) 4 1 Fosc/8 2 24 8 5 Fosc/16 2 24 10 5 Fosc/16 1.6 19.2 12 2 Fosc/32 2.6 31.2 16 2 Fosc/32 2 24 20 2 Fosc/32 1.6 19.2 24 6 Fosc/64 2.6 31.2 32 6 Fosc/64 2 24 40 6 Fosc/64 1.6 19..2 48 3 FRC 4 48us
Noise in the system:
As previously mentioned, it's the number of times the value bounces back and forth between two numbers that allows it to gain more bits of resolution.
If (due to poor design) your A/D values are swinging wildly even at normal 10-bit, this system will also help calm them down (some) since it will find an average of the samples taken. Usually it's the mid-point of those swings that you want to find anyway. Naturally, you should minimize ALL noise as much as possible to begin with.
Using the Module:
You must first configure your PIC to have the desired Analog inputs and use the correct Oscillator source. This module will not do it for you.
You must also set the ADC DEFINE's for the fastest available 10-bit results, depending on your oscillator frequency.
Then INCLUDE the file somewhere near the top of your program.
Set the ADchan variable to the AN channel you wish to read. (ADchan = 1)
Set the ADbits variable to the desired resolution. (ADbits = 12)
Then GOSUB GetADC.
The resulting value will be returned in the ADvalue word sized variable.
And the maximum A/D value for the selected resolution is returned in the ADmax variable.
************************************************** ***************************Code:'http://www.darreltaylor.com/DT_Analog/ '**************************************************************** '* Name : DT_Analog.pbp * '* Author : Darrel Taylor * '* Notice : Copyright (c) 2009 * '* Date : 5/23/2009 * '* Version : 1.0 * '* Notes : Up to 16 bit A/D with a 10-bit A/D converter * '* : http://en.wikipedia.org/wiki/Oversampling * '**************************************************************** GOTO OverDTAnalog ADchan VAR BYTE ; global - A/D channel to use ADbits VAR BYTE ; global - # of bits in result ADvalue VAR WORD ; global - the final A/D value ADmax VAR WORD ; global - Max A/D value at this resolution ;-------------------- DTadCount VAR WORD ; local - sample count DTadDivisor VAR WORD ; local - averaging divisor DTadShiftR VAR BYTE ; local - bits to shift for UnderSampling DTadAccum VAR WORD[2] ; local - 32-bit sample accumulator ;--------------------------------------------------------------------------- GetADC: IF (ADbits >= 10) THEN DTadShiftR = 0 ; 10 11 12 13 14 15 16 LOOKUP2 ADbits-10,[ 1, 4,16,64,256,1024,4096],DTadCount LOOKUP ADbits-10,[ 1, 2, 4, 8, 16, 32, 64],DTadDivisor ELSE DTadCount = 1 DTadDivisor = 1 DTadShiftR = 10 - ADbits ENDIF LOOKUP2 ADbits,[0,1,3,7,15,31,63,127,255,511,1023, _ 2046,4092,8184,16368,32736,65472],ADmax DTadAccum = 0 : DTadAccum[1] = 0 ; clear the accumulator DTadLoop: ADCIN ADchan, ADvalue ; get 10-bit sample DTadAccum = DTadAccum + ADvalue ; add it to the accumulator IF DTadAccum < ADvalue THEN ; if low word overflowed DTadAccum[1] = DTadAccum[1] + 1 ; increment the high word ENDIF DTadCount = DTadCount - 1 ; done with this sample IF DTadCount > 0 THEN DTadLoop ; loop if not done with ALL samples R2 = DTadAccum ; put 32-bit accumulated value in PBP R0 = DTadAccum[1] ; registers, prepare for DIV32 ADvalue = DIV32 DTadDivisor ; get the average value ADvalue = ADvalue >> DTadShiftR ; Shift right if < 10-bit RETURN OverDTAnalog:
************************************************** ***************************
************************************************** ********************************Code:Here's a simple example that displays 12-bit A/D values on an LCD. Of course, by changing one number it will display 16-bit values too. Download 12-bit example Download example code. (Save it to a new folder. Not the PBP folder) View 12-bit DEMO in browser View ;--- Set your __configs here as needed --- DEFINE OSC 20 INCLUDE "DT_Analog.pbp" ; DT's 16-bit Analog Module DEFINE ADC_BITS 10 ; Set-up ADC for fast 10-bit results DEFINE ADC_CLOCK 2 DEFINE ADC_SAMPLEUS 5 ;----[Change these to match your hardware]---------------------------------- DEFINE LCD_DREG PORTB ; LCD Data Port DEFINE LCD_DBIT 0 ; Starting Data Bit DEFINE LCD_RSREG PORTB ; Register Select Port DEFINE LCD_RSBIT 4 ; Register Select Bit DEFINE LCD_EREG PORTB ; Enable Port DEFINE LCD_EBIT 5 ; Enable Bit DEFINE LCD_BITS 4 ; Data Bus Size DEFINE LCD_LINES 2 ; Number of Lines on LCD DEFINE LCD_COMMANDUS 2000 ; Command Delay time in uS DEFINE LCD_DATAUS 50 ; Data Delay time in uS ADCON1 = %10001101 ; right justify, AN0 & AN1 analog PAUSE 250 : LCDOUT $FE,1 ; Initialize LCD PAUSE 100 : LCDOUT $FE,1 ; not all LCDs need both lines ADbits = 12 ; set to 12-bit resolution ;--------------------------------------------------------------------------- Main: FOR ADchan = 0 to 1 ; Do both AN0 and AN1 GOSUB GetADC ; Get A/D value IF ADchan = 0 THEN LCDOUT $FE, $80 ; LCD line 1 ELSE LCDOUT $FE, $C0 ; LCD line 2 ENDIF LCDOUT "CH-",DEC1 ADchan," = ",DEC ADvalue," " NEXT ADchan GOTO Main:
************************************************** ********************************
************************************************** ********************Code:Here's another example that shows all the resolutions from 1-16 bit from a single A/D channel via the USART with HyperTerminal or other ANSI terminal program. Download ALL-bit example Download example code. (Save it to a new folder. Not the PBP folder) View ALL-bit DEMO in browser View ;--- Set your __configs here as needed --- DEFINE OSC 20 INCLUDE "DT_Analog.pbp" ; DT's 16-bit Analog Module DEFINE ADC_BITS 10 DEFINE ADC_CLOCK 2 DEFINE ADC_SAMPLEUS 5 DEFINE HSER_SPBRG 10 ; 115200 @ 20 Mhz DEFINE HSER_RCSTA 90h ; Hser receive status init DEFINE HSER_TXSTA 24h ; Hser transmit status init DEFINE HSER_CLROERR 1 ; Hser clear overflow automatically Volts VAR WORD ; Volts calculated from the A/D reading ADCON1 = %10001101 ; right justify, AN0 & AN1 analog HSEROUT [27,"[2J"] ; Clear screen ;--------------------------------------------------------------------------- Main: HSEROUT [27,"[H"] ; home cursor HSEROUT [27,"[34m",27,"[1m"] ; bold blue text HSEROUT ["ADbits DEC HEX BIN16 ADmax Volts"] HSEROUT [27,"[37m",13,10] ; black text ADchan = 1 ; Select channel AN1 FOR ADbits = 1 to 16 ; cycle thru all bit resolutions GOSUB GetADC ; get the A/D value GOSUB ShowAD ; show the A/D results NEXT ADbits ; do next resolution GOTO Main ;--------------------------------------------------------------------------- ShowAD: IF ADbits < 10 THEN HSEROUT [" "] HSEROUT [DEC ADbits,"-bit = ",DEC ADvalue," "] HSEROUT [27,"[",DEC ADbits+1,";16H",HEX4 ADvalue," ",BIN16 ADvalue, _ " ",DEC ADmax] IF ADbits < 16 THEN ; calculate the Voltage with 4 decimals Volts = 50000 * ADvalue Volts = DIV32 ADmax ELSE ; with 16-bit, ADmax is too big for DIV32 ADmax = ADmax >> 1 ; cut it in half Volts = 25000 * ADvalue ; and scale the multiplier accordingly Volts = DIV32 ADmax ; PBPL & Longs, doesn't have that problem ENDIF HSEROUT [27,"[",DEC ADbits+1,";49H", _ DEC Volts/10000,".",DEC4 Volts//10000 ,13,10] RETURN This is a screen shot of the ALLBitDEMO in action. And before you ask Charles ... This will not work (as is) on a PIC with a 12-bit A/D converter.
************************************************** ********************
Code:'http://www.darreltaylor.com/DT_Analog/ '**************************************************************** '* Name : AllBitDEMO.pbp * '* Author : Darrel Taylor * '* Notice : Copyright (c) 2009 * '* Date : 5/24/2009 * '* Version : 1.0 * '* Notes : Example program for DT_Analog.pbp * '* Displays all possible A/D resolutions for a single * '* channel using the USART and HyperTerminal or other * '* ANSI terminal program * '**************************************************************** ;--- Set your __configs here as needed --- DEFINE OSC 20 INCLUDE "DT_Analog.pbp" ; DT's 16-bit Analog Module DEFINE ADC_BITS 10 DEFINE ADC_CLOCK 2 DEFINE ADC_SAMPLEUS 5 DEFINE HSER_SPBRG 10 ; 115200 @ 20 Mhz DEFINE HSER_RCSTA 90h ; Hser receive status init DEFINE HSER_TXSTA 24h ; Hser transmit status init DEFINE HSER_CLROERR 1 ; Hser clear overflow automatically Volts VAR WORD ; Volts calculated from the A/D reading ADCON1 = %10001101 ; right justify, AN0 & AN1 analog HSEROUT [27,"[2J"] ; Clear screen ;--------------------------------------------------------------------------- Main: HSEROUT [27,"[H"] ; home cursor HSEROUT [27,"[34m",27,"[1m"] ; bold blue text HSEROUT ["ADbits DEC HEX BIN16 ADmax Volts"] HSEROUT [27,"[37m",13,10] ; black text ADchan = 1 ; Select channel AN1 FOR ADbits = 1 to 16 ; cycle thru all bit resolutions GOSUB GetADC ; get the A/D value GOSUB ShowAD ; show the A/D results NEXT ADbits ; do next resolution GOTO Main ;--------------------------------------------------------------------------- ShowAD: IF ADbits < 10 THEN HSEROUT [" "] HSEROUT [DEC ADbits,"-bit = ",DEC ADvalue," "] HSEROUT [27,"[",DEC ADbits+1,";16H",HEX4 ADvalue," ",BIN16 ADvalue, _ " ",DEC ADmax] IF ADbits < 16 THEN ; calculate the Voltage with 4 decimals Volts = 50000 * ADvalue Volts = DIV32 ADmax ELSE ; with 16-bit, ADmax is too big for DIV32 ADmax = ADmax >> 1 ; cut it in half Volts = 25000 * ADvalue ; and scale the multiplier accordingly Volts = DIV32 ADmax ; PBPL & Longs, doesn't have that problem ENDIF HSEROUT [27,"[",DEC ADbits+1,";49H", _ DEC Volts/10000,".",DEC4 Volts//10000 ,13,10] RETURN
Reply With Quote
Bookmarks