Dual PII-S

Making CPU Temperature Sensors for the P2B Series


Asus P2B series motherboards do not support temperature monitoring of the thermal diode available in many Intel processors, however they are able to monitor CPU temperature externally using a thermistor connected to the JTCPU header (May be labelled differently on some versions, e.g. the P2B-D and P2B-DS have headers for both CPUs, labelled JP4 and JP5). While it is possible to connect CPU thermal diodes to the CPU temperature monitoring headers, this is difficult as it requires a moderately complex interface circuit installed on a modified slot-1 adapter. Using external thermistors is considerably easier!

External thermistors cannot provide an accurate reading of CPU core temperature, however they do provide a useful relative indication of normal CPU operating temperature and can alert the user to abnormal increases in temperature which may be indicative of a cooling problem.

Choosing a Thermistor

The Asus P2B series boards were designed to use 10K ohm thermistors for CPU temperature monitoring. At least two styles of thermistor are available.

Thermistor Types
 The green 10K ohm thermistor (top) is a pigtail type, available at Radio Shack. This type is not ideal for P2B series boards running Socket 370 processors as it is too thick to fit close to the CPU core.

Red axial lead 10K ohm thermistors (bottom) are not as commonly available, but are better suited to this application as they fit between the CPU and heatsink.

Parts List

Parts List
The parts required to make a CPU temperature sensor for the Asus P2B are shown at left and can be obtained from any good electronic component supplier (Radio Shack does not qualify)

  • Axial lead thermistor, 10K ohms
  • Twisted pair cable 15cm long
  • Two header pins
  • Two-pin header casing
  • Heatshrink tubing, 3mm diameter, 2cm long (not shown)

The two-pin reset or power switch cabling from a discarded ATX PC case can be used in lieu of new parts if desired, reducing the parts list to just thermistor and heatshrink tubing.

Assembly

Thermistor Leads
 Assembling the CPU temperature sensor is straightforward.



First bend and trim the thermistor leads as shown.
Thermistor Soldering




Next solder one end of the twisted pair cable to the thermistor leads.
Pin Soldering






Then solder the header pins to the other end of the twisted pair cable. Crimp the lugs onto the insulated portion of the wires to provide strain relief.
Completed Sensor





Finally, insert the pins into the header casing, slide heatshrink tubing over the thermistor, and warm the tubing with a hair dryer to fix it in place.

Installation

To install the CPU temperature sensor, simply connect the two-pin header to the appropriate motherboard connector, and place the thermistor as close as possbile to the CPU core. The thermistor will fit between a Socket 370 CPU and it's heatsink and can be placed against the CPU heat spreader as shown below.

Installed Sensor

 Last updated April 3rd, 2004 by p2b@sympatico.ca