update. Clarify that w83782d/783s support both thermistors

and diodes but must be configured for one or the other.


git-svn-id: http://lm-sensors.org/svn/lm-sensors/trunk@425 7894878c-1315-0410-8ee3-d5d059ff63e0

1 files changed, 38 insertions, 8 deletions

diff --git a/doc/temperature-sensors b/doc/temperature-sensors
index 709a05cc..374ece87 100644
--- a/doc/temperature-sensors
+++ b/doc/temperature-sensors
@@ -2,17 +2,19 @@ Termistor and Transistors as Temperature Sensors
 ------------------------------------------------
 Temperature measuring chips that use external sensors
 generally are designed to use either thermistors or
-transistors.
+transistors. Check the driver documentation in doc/chips
+or the actual data sheets to determine which.
 
-Exceptions are the Winbond W83782D and W83783S which claim
-to be able to use both, however it isn't clear how
-to configure these to use transistors.
+Exceptions are the Winbond W83782D and W83783S which can use either.
+These chips default to termistors but can be configured to use
+Pentium II / Celeron diodes or 3904 transistors.
 
+Thermistors are about 10 times more sensitive than
+diodes or transistors at room temperature.
 
 
 Thermistors
 -----------
-
 (summarized from http://www.thermometrics.com/htmldocs/ntcapp.htm  -
  most thermistor companies don't have much on their web sites but
  Thermometrics has a comprehensive guide)
@@ -38,15 +40,16 @@ A = - B / T**2
 
 So by the last equation, a thermistor with a Beta of 3900 will change
 resistance about 4.4% for 1 degree change at 25C (298K).
-For a beta of 3423 as recommended in the 782D data sheet the change is 3.8%.
+For a beta of 3435 as recommended in the
+Winbond W83782D data sheet the change is 3.8%.
 
 For thermistors, resistance (= voltage for a constant current)
 is exponentially related to temperature.
 
 
 
-Transistors
---------------
+Transistors / Diodes
+--------------------
 To use a transistor as a sensor, hook the base of an NPN transistor
 (such as the 3904) to the collector.
 
@@ -67,3 +70,30 @@ For diodes, voltage is linear with temperature.
 
 
 
+Winbond W83782D and W83783S
+---------------------------
+These chips default to thermistors with Beta = 3435.
+Each sensor on the chip can be individually set to be 
+a diode, transistor, or thermistor.
+If the temperature reading changes much less than expected,
+the sensor type probably needs to be changed to a diode.
+See doc/chips/w83781d for details.
+
+
+Summary
+-------
+Thermistors are about 10 times more sensitive than
+diodes or transistors at room temperature.
+
+Thermistors change resistance exponentially with respect to temperature.
+Diodes and transistors change voltage linearly with respect to temperature.
+
+Sensors built into chips (including Pentium II / Celeron processors)
+are always diodes/transistors because that's what's on a chip
+already - transistors.
+
+External, discrete sensors can be either diodes/transistors or
+thermistors. Generally, sensor chips are designed to be connected
+to one or the other and cannot be configured. The Winbond
+W83782D/W83783S chips are exceptions, they can be
+configured for either.