firmware: add experimental software debounce.

Suspected EMI transients have been observed spuriously triggering the
external interrupt lines on some systems.  Likely this is better solved
in hardware, however this is not as convenient as a software fix.

When enabled, ISRs first delay by a fixed about (~1.2ms currently) and
then inspects the active-low interrupting pin.  The delay amount
was selected somewhat empirically (with a non-SF800 sensor) and
likely requires tuning to account for differences in sensors.

arduino/kegboard/kegboard.ino

@@ -45,7 +45,6 @@
 #include <util/crc16.h>
 #include <util/delay.h>
 
-
 #include "kegboard.h"
 #include "kegboard_config.h"
 #include "ds1820.h"
@@ -197,43 +196,55 @@ static unsigned long gLastWiegandInterruptMillis = 0;
 // ISRs
 //
 
+#if KB_ENABLE_SOFT_DEBOUNCE
+#define CHECK_METER(pin, meter_index)                   \
+  do {                                                  \
+    delayMicroseconds(KB_SOFT_DEBOUNCE_MICROS);         \
+    if (digitalRead(pin) == 0)                          \
+      gMeters[meter_index] += 1;                        \
+  } while(0)
+#else
+#define CHECK_METER(pin, meter_index)                   \
+  gMeters[meter_index] += 1
+#endif
+
 void meterInterruptA()
 {
-  gMeters[0] += 1;
+  CHECK_METER(KB_PIN_METER_A, 0);
 }
 
 #ifdef KB_PIN_METER_B
 void meterInterruptB()
 {
-  gMeters[1] += 1;
+  CHECK_METER(KB_PIN_METER_B, 1);
 }
 #endif
 
 #ifdef KB_PIN_METER_C
 void meterInterruptC()
 {
-  gMeters[2] += 1;
+  CHECK_METER(KB_PIN_METER_C, 2);
 }
 #endif
 
 #ifdef KB_PIN_METER_D
 void meterInterruptD()
 {
-  gMeters[3] += 1;
+  CHECK_METER(KB_PIN_METER_D, 3);
 }
 #endif
 
 #ifdef KB_PIN_METER_E
 void meterInterruptE()
 {
-  gMeters[4] += 1;
+  CHECK_METER(KB_PIN_METER_E, 4);
 }
 #endif
 
 #ifdef KB_PIN_METER_F
 void meterInterruptF()
 {
-  gMeters[5] += 1;
+  CHECK_METER(KB_PIN_METER_F, 1);
 }
 #endif
 
@@ -386,36 +397,36 @@ void setup()
   // from ticking away.
   pinMode(KB_PIN_METER_A, INPUT);
   digitalWrite(KB_PIN_METER_A, HIGH);
-  attachInterrupt(0, meterInterruptA, RISING);
+  attachInterrupt(0, meterInterruptA, FALLING);
 
 #ifdef KB_PIN_METER_B
   pinMode(KB_PIN_METER_B, INPUT);
   digitalWrite(KB_PIN_METER_B, HIGH);
-  attachInterrupt(1, meterInterruptB, RISING);
+  attachInterrupt(1, meterInterruptB, FALLING);
 #endif
 
 #ifdef KB_PIN_METER_C
   pinMode(KB_PIN_METER_C, INPUT);
   digitalWrite(KB_PIN_METER_C, HIGH);
-  attachInterrupt(2, meterInterruptC, RISING);
+  attachInterrupt(2, meterInterruptC, FALLING);
 #endif
 
 #ifdef KB_PIN_METER_D
   pinMode(KB_PIN_METER_D, INPUT);
   digitalWrite(KB_PIN_METER_D, HIGH);
-  attachInterrupt(3, meterInterruptD, RISING);
+  attachInterrupt(3, meterInterruptD, FALLING);
 #endif
 
 #ifdef KB_PIN_METER_E
   pinMode(KB_PIN_METER_E, INPUT);
   digitalWrite(KB_PIN_METER_E, HIGH);
-  attachInterrupt(4, meterInterruptE, RISING);
+  attachInterrupt(4, meterInterruptE, FALLING);
 #endif
 
 #ifdef KB_PIN_METER_F
   pinMode(KB_PIN_METER_F, INPUT);
   digitalWrite(KB_PIN_METER_F, HIGH);
-  attachInterrupt(5, meterInterruptF, RISING);
+  attachInterrupt(5, meterInterruptF, FALLING);
 #endif
 
   pinMode(KB_PIN_RELAY_A, OUTPUT);

arduino/kegboard/kegboard_config.h

@@ -27,6 +27,14 @@
 // Note: Must set KB_ENABLE_ID12_RFID to 0 if enabling this.
 #define KB_ENABLE_WIEGAND_RFID 0
 
+// Enable software debounce? EXPERIMENTAL. Enabling this feature may negatively
+// affect pour accuracy.  In particular, a delay is added to each flow meter
+// ISR, disabling all other interrupts during this time.
+#define KB_ENABLE_SOFT_DEBOUNCE 0
+
+// Approximate minimum pulse width required for incoming external interrupts.
+#define KB_SOFT_DEBOUNCE_MICROS 1200
+
 //
 // Pin configuration - KEGBOARD VERSION
 //

docs/source/changelog.rst

@@ -6,6 +6,11 @@ Changelog
 Arduino Firmware
 -----------------
 
+Current Version (in development)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+* Flow LEDs are now toggled on system startup and during pours.
+* Experimental debounce feature.
+
 v13 (2012-10-28)
 ^^^^^^^^^^^^^^^^
 * Adds support for Wiegand RFID readers (HID ProxPro and similar).