X-Git-Url: https://oss.titaniummirror.com/gitweb/?a=blobdiff_plain;f=tos%2Fplatforms%2Ftmirws%2Fsensors%2FWindVaneAdcP.nc;h=67f019df5f7404c979dd95cb62064a0ecc1644ce;hb=f6c92b59f03adcffc10b150474f9a7062be5ca30;hp=a80362bad34021a7db41aea82dacd40b86718b44;hpb=4f0def622af5baa14e297eac8f3fb695b0a25bb7;p=tinyos-2.x.git

diff --git a/tos/platforms/tmirws/sensors/WindVaneAdcP.nc b/tos/platforms/tmirws/sensors/WindVaneAdcP.nc
index a80362ba..67f019df 100644
--- a/tos/platforms/tmirws/sensors/WindVaneAdcP.nc
+++ b/tos/platforms/tmirws/sensors/WindVaneAdcP.nc
@@ -28,42 +28,43 @@
  */
  
 /**
- * Battery ADC reading.
+ * Reads the ADC pin connected to the Davis Instruments anemometer.  The
+ * connection is made via a resistor divider.  The voltage seen by the ADC
+ * is related to VREF, the maximum voltage presented to the ADC.
+ * 0V or VREF means North
+ * VREF*1/4 means East
+ * VREF*2/4 means South
+ * VREF*3/4 means West
+ *
+ * We assume a 12-bit ADC, so VREF reads as 4095 and 0V reads as 0.
  * 
  * @author R. Steve McKown <rsmckown@gmail.com>
  */
  
 #include "Msp430Adc12.h"
 
-module BatteryAdcP {
+module WindVaneAdcP {
   provides interface AdcConfigure<const msp430adc12_channel_config_t*>;
 }
 implementation {
-  /* TODO: The internal references are unsable, varying by more than 0.1V and
-   * jumping around.  The external reference of 2.50V seems stable.
+  /* We use the external reference because it is probably more accurate (see
+   * the circuit), and there is no arbitration for the voltage reference.  With
+   * the external reference, we can ReadStream 4 data points in 420 us.  Using
+   * the internal reference, this time increases significantly to over 18 ms.
    */
   const msp430adc12_channel_config_t config = {
-      inch: INPUT_CHANNEL_A0,
-#if 0 /* internal references unstable */
-      sref: REFERENCE_VREFplus_AVss,
-      ref2_5v: REFVOLT_LEVEL_1_5, /* REFVOLT_LEVEL_2_5, */
-#else /* external reference is stable */
+      inch: INPUT_CHANNEL_A2,
       sref: REFERENCE_VeREFplus_AVss,
-      ref2_5v: REFVOLT_LEVEL_1_5,
-#endif
-#if 0 /* clock source doesn't seem to affect stability */
+      ref2_5v: REFVOLT_LEVEL_1_5, /* doesn't matter since external ref used */
       adc12ssel: SHT_SOURCE_ADC12OSC,
       adc12div: SHT_CLOCK_DIV_8,
-#else
-      adc12ssel: SHT_SOURCE_ACLK,
-      adc12div: SHT_CLOCK_DIV_1,
-#endif
       sht: SAMPLE_HOLD_8_CYCLES,
       sampcon_ssel: SAMPCON_SOURCE_ACLK,
       sampcon_id: SAMPCON_CLOCK_DIV_1
   };
   
-  async command const msp430adc12_channel_config_t* AdcConfigure.getConfiguration()
+  async command const msp430adc12_channel_config_t*
+    AdcConfigure.getConfiguration()
   {
     return &config;
   }