BillA-unregistered...how accurate is the XP's thermal diode?

[bigben2k]

Certainly! (tmo)

[pHaestus]

dallas 1 wire isn't the same as the CPU's internal diode as far as I know. The 1wire temp sensors are basically independent little digital thermometers in a typical transistor package. They work well because the sensor just needs voltage from the reader and a wire to transmit the temperature back. This means a lot of the problems associated with diode readers (trace width/length and solder points) are no longer a concern. The 1wire sensors I have are 0.5C accuracy and 0.125C resolution though; haven't seen any info on getting better than the mfgr's stated limits on them.

FYI, my approach to dealing with diode calibration is to basically epoxy one of those 1 wire sensors (or now, thanks to Bill, a type T thermocouple) under the center of a ceramic AMD CPU. There are equations relating the CPU die temp to the CPU backside temp for the ceramic CPUs supplied by AMD. The relationship can be used to cross correlate the diode.

Not so sure about soldering onto CPU pins Ben. I know PeterNorth killed an XP's diode by soldering onto the socket with the CPU in it. Not sure how you get a perfect connect of wire to CPU pin without soldering either. If you really wanted to get a diode reader cobbled onto a mobo that had "COP" or such, then I would pull the metal connection out of the socket and then just wire wrap the CPU and use a thin piece of heatshrink. Will the motherboard still boot without a diode temp reading though? This actually isnt a bad approach if you can get a perfect coupling of wire to pin because you could then use a water bath to calibrate the diode.

[Les]

Originally posted by pHaestus
There are equations relating the CPU die temp to the CPU backside temp for the ceramic CPUs supplied by AMD. The relationship can be used to cross correlate the diode.

Not sure, but I think the constants in the equations depend on the "thermal performance of the heatsink used". This is both my understanding of the significance of the backside temp and my reading of AMD's pdf document 24228 (particularly pages 33-34*. If this so then the backside temp cannot be used to calibrate. Think some careful thought is required.

* http://www.amd.com/us-en/assets/cont...docs/24228.pdf

[W1zzard]

personally i have built a few maxim based diode readers ...

suggested ics are maxim max6657/6658/6659 series ..
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578

if you want to use the internal diode on a board that already has a diode reader use desoldering braid (correct term?) on the dxp/dxn pins of your motherboards temp management ic to remove as much solder as possible ... then put a razor blade under the pin and bend it up just a very little.. only so much that the connection is gone .. now solder your wires to the back of you mobo cpu socket... very easy to undo ...