Diff: main.cpp
- Revision:
- 1:ecca38babc13
- Parent:
- 0:7c70badd2847
- Child:
- 2:e1781d02ec0d
--- a/main.cpp Wed Feb 16 23:20:42 2011 +0000
+++ b/main.cpp Fri Feb 18 00:43:05 2011 +0000
@@ -10,7 +10,14 @@
by a "vote" taken from three successive readings.
3) Introduces a "glitch" suppression method that appears
- to be effective.
+ to be effective. I consider a glitch to have occurred
+ when two consecutive reading differ in value by more than
+ 3 sigma (approximately 10 for the noise distributions
+ exhibited by the internal ADC).
+
+ 4) Provides for side-by-side comparison of an external ADC
+ (MCP3304 or MCP3208) running at about 20,000 sps (because
+ I'm running the part at 3.3v).
With a 100nf capacitor from the analog pin to ground and
a reasonably low impedance source ( < 5K ) and glitch suppression
@@ -20,25 +27,39 @@
cleanest of inputs. This program will help you determine for
yourself whether that statement is true. Play with it.
+The comparison of the internal ADC with the external ADC show that the
+external ADC is well behaved in circumstances that wipe out the internal ADC
+which is apparently quite sensitive to noise, whereas the external ADC is quite
+tolerant of noise. The external ADC produces very narrow "distributions".
+
*/
#include "mbed.h"
-#include "Serial.h"
-#include "AnalogIn.h"
Serial pc( USBTX, USBRX );
AnalogIn ain( p20 );
+DigitalOut mpc3304Select(p8);
+DigitalOut led4(LED4);
+
+SPI spi(p5,p6,p7); // spi(mosi,miso,sck)
+
#define NUM_SAMPLES 1000000
#define HGRAM_MAX_INDEX 60
-int histoGram[ HGRAM_MAX_INDEX + 1 ];
+
+int histoGramA[ HGRAM_MAX_INDEX + 1 ]; // histogram array for internal ADC
+int histoGramB[ HGRAM_MAX_INDEX + 1 ]; // histogram array for (possible) external ADC
int glitchCount = 0;
bool glitchSuppressionWanted = false;
+bool useExternalADC = false;
-void setADCclockToMaxConversionRate(void);
-int glitchSuppressedAnalogIn( void );
+void setADCclockToMaxConversionRate( void );
+int glitchSuppressedAnalogIn( bool );
+int readExternalADC( void );
+void displayMenu( void );
+int getCenterValue( bool externalADC );
int max( int a, int b ) {
if ( a > b ) return a;
@@ -55,20 +76,33 @@
return (a <= max(b,c)) && (a >= min(b,c));
}
+// The MPC3304 chip select line is inverted: low == selected
+#define EXT_ADC_OFF 1
+#define EXT_ADC_ON 0
+
+
+
int main() {
int referenceValue;
int delta;
int newValue;
+ led4 = 0; // This led shows progress during data acquisition.
+
+ mpc3304Select = EXT_ADC_OFF; // deselect
+
+ spi.format( 8, 0 );
+ spi.frequency( 500000 );
+
// Speedup the AnalogIn conversion rate by readjusting
// the ADC clock to 12 MHz (assuming SystemCoreClock = 96MHz)
setADCclockToMaxConversionRate();
while(1) {
-
- printf( "\nPress the s key to start stats gathering\n" );
- printf( "Press the g key to toggle glitch suppression...\n" );
+
+ displayMenu();
+
bool waitingForKeyInput = true;
while ( waitingForKeyInput ){
@@ -77,52 +111,97 @@
case 'G':
glitchSuppressionWanted = ! glitchSuppressionWanted;
if ( glitchSuppressionWanted )
- printf( "...glitch suppression on...\n" );
+ printf( "...glitch suppression on...\r\n" );
else
- printf( "...glitch suppression off...\n" );
+ printf( "...glitch suppression off...\r\n" );
+ break;
+
+ case 'x':
+ case 'X':
+ useExternalADC = ! useExternalADC;
+ if ( useExternalADC )
+ printf( "...external ADC will be used...\r\n\r\n" );
+ else
+ printf( "...only internal ADC will be used...\r\n" );
+ break;
+
+ case 't':
+ for ( int cnt = 0; cnt < 50; cnt++ )
+ printf( "EXT ADC = %d\r\n", readExternalADC() );
break;
+
case 's':
- case 'S': waitingForKeyInput = false;
+ case 'S': waitingForKeyInput = false; break;
+
+ default:
+ displayMenu(); break;
}
}
+
+ // Clear the histogram arrays.
+ for ( int k = 0; k <= HGRAM_MAX_INDEX; k++ ) histoGramA[k] = histoGramB[k] = 0;
+
+ bool readFromExternalADC = false;
+
+ referenceValue = getCenterValue( readFromExternalADC );
+
+ printf( "Internal ADC center value = %d\r\n\r\n", referenceValue );
+ printf( "...now gathering... LED4 toggles at each 10,000 readings\r\n\r\n" );
+
+ glitchCount = 0;
+ for ( int i = 0; i < NUM_SAMPLES; i++ ) {
+ newValue = glitchSuppressedAnalogIn( readFromExternalADC );
+ delta = newValue - referenceValue + (HGRAM_MAX_INDEX / 2);
+ if ( delta < 0 ) histoGramA[0]++;
+ else if ( delta > HGRAM_MAX_INDEX ) histoGramA[HGRAM_MAX_INDEX]++;
+ else histoGramA[delta]++;
+ if ( (i % 10000) == 0 ) led4 = !led4;
+ }
+ led4 = 0;
+
+ int glitchCountInternal = glitchCount;
+ int glitchCountExternal;
+
+ if ( useExternalADC )
+ {
+ readFromExternalADC = true;
+
+ referenceValue = getCenterValue( readFromExternalADC );
+
+ printf( "External ADC center value = %d\r\n\r\n", referenceValue );
+ printf( "...now gathering... LED4 toggles at each 10,000 readings\r\n\r\n" );
+
+ glitchCount = 0;
+ for ( int i = 0; i < NUM_SAMPLES; i++ ) {
+ newValue = glitchSuppressedAnalogIn( readFromExternalADC );
+ delta = newValue - referenceValue + (HGRAM_MAX_INDEX / 2);
+ if ( delta < 0 ) histoGramB[0]++;
+ else if ( delta > HGRAM_MAX_INDEX ) histoGramB[HGRAM_MAX_INDEX]++;
+ else histoGramB[delta]++;
+ if ( (i % 10000) == 0 ) led4 = !led4;
+ }
+ led4 = 0;
+
+ glitchCountExternal = glitchCount;
+ }
- // Establish center point for histogram by taking three readings
- // and selecting the one in the middle as the reference value around
- // which deviations will be calculated.
- int value1 = ain.read_u16() >> 4;
- int value2 = ain.read_u16() >> 4;
- int value3 = ain.read_u16() >> 4;
-
- if ( middle(value1,value2,value3) )
- referenceValue = value1;
- else if ( middle(value2,value1,value3) )
- referenceValue = value2;
- else
- referenceValue = value3;
-
- printf( "\nreferenceValue: %d value1: %d value2: %d value3: %d\n",
- referenceValue, value1, value2, value3 );
- printf( "\n...now gathering...\n\n" );
-
- // Clear the histogram array.
- for ( int k = 0; k <= HGRAM_MAX_INDEX; k++ ) histoGram[k] = 0;
- glitchCount = 0;
-
- for ( int i = 0; i < NUM_SAMPLES; i++ ) {
- newValue = glitchSuppressedAnalogIn();
- delta = newValue - referenceValue + (HGRAM_MAX_INDEX / 2);
- if ( delta < 0 ) histoGram[0]++;
- else if ( delta > HGRAM_MAX_INDEX ) histoGram[HGRAM_MAX_INDEX]++;
- else histoGram[delta]++;
- }
// Output histoGram
for ( int j = 0; j <= HGRAM_MAX_INDEX; j++ ) {
- printf( "%4d %8d\n", j, histoGram[j] );
+ if ( useExternalADC )
+ printf( "%4d %8d %8d\r\n", j - (HGRAM_MAX_INDEX/2), histoGramA[j], histoGramB[j] );
+ else
+ printf( "%4d %8d\r\n", j - (HGRAM_MAX_INDEX/2), histoGramA[j] );
}
- printf( "glitchCount: %d\n", glitchCount );
+ if ( glitchSuppressionWanted ) {
+ if ( useExternalADC )
+ printf( "\nglitchCount: Internal = %d External = %d\r\n",
+ glitchCountInternal, glitchCountExternal );
+ else
+ printf( "\nglitchCountInternal = %d\r\n", glitchCountInternal );
+ }
}
}
@@ -141,10 +220,14 @@
return;
}
-int glitchSuppressedAnalogIn( void ) {
+int glitchSuppressedAnalogIn( bool externalADC ) {
int v1,v2,delta;
- v1 = ain.read_u16() >> 4;
+ if ( externalADC )
+ v1 = readExternalADC();
+ else
+ v1 = ain.read_u16() >> 4;
+
if ( ! glitchSuppressionWanted ) return v1;
// While this has the possiblity of never returning,
@@ -152,10 +235,56 @@
// that we will eventually find two successive readings that are
// within the tolerance band --- i.e., no glitch
while(1){
- v2 = ain.read_u16() >> 4;
+ if ( externalADC )
+ v2 = readExternalADC();
+ else
+ v2 = ain.read_u16() >> 4;
delta = v1 - v2;
if ( (delta > -10) && (delta < 10)) return (v1+v2)/2;
v1 = v2;
glitchCount++;
}
+}
+
+int readExternalADC( void ) { // Hardcoded for channel 0 (for quick test)
+ mpc3304Select = EXT_ADC_ON;
+ int byte1 = spi.write( 0xc ); // start=1 sgl=1 d2=0 d1=0
+ int byte2 = spi.write( 0x0 ) & 0xf; // d0 = 0
+ int byte3 = spi.write( 0xaa ); // dummy value, but nice pattern of logic analyzer
+ mpc3304Select = EXT_ADC_OFF;
+ int value = (byte2 << 8) | byte3;
+ //printf( "byte2 = %2x byte3 = %2x value = %d\r\n", byte2, byte3, value );
+ return value;
+}
+
+void displayMenu( void ) {
+
+ if ( glitchSuppressionWanted )
+ printf( "\r\n\r\nglitch suppression is enabled.\r\n" );
+ else
+ printf( "\r\nglitch suppression is disabled\r\n" );
+ if ( useExternalADC )
+ printf( "Results from an external ADC will be included.\r\n" );
+ else
+ printf( "External ADC not in use.\r\n" );
+
+ printf( "\r\nPress the s key to start data acquisition.\r\n" );
+ printf( "Press the g key to toggle glitch suppression.\r\n" );
+ printf( "Press the x key to toggle use of external ADC.\r\n\r\n" );
+}
+
+int getCenterValue( bool externalADC ) {
+ // Establish center point for histogram by taking three readings
+ // and selecting the one in the middle as the reference value around
+ // which deviations will be calculated.
+ int value1 = glitchSuppressedAnalogIn( externalADC );
+ int value2 = glitchSuppressedAnalogIn( externalADC );
+ int value3 = glitchSuppressedAnalogIn( externalADC );
+
+ if ( middle(value1,value2,value3) )
+ return value1;
+ else if ( middle(value2,value1,value3) )
+ return value2;
+ else
+ return value3;
}
\ No newline at end of file
Bob Anderson