Radio Shack CPU temp monitors

This page sucks, but it's mainly a reference so I don't have to post the same thing over and over in the newsgroups and messageboards when someone asks "How do you monitor your temps w/o software?", so here it is.

System cooling:
120mm Delta intake (filtered) at lower front of case.
120mm Delta intake (filtered) above power supply. This one is ducted to the CPU base.
92mm Sunon exhaust behind CPU.
2CoolPC 92mm ducted fan brings air from lower 120mm to AGP area.
Tennmax BGA cooler on Geforce 256 DDR.
Tennmax BGA cooler on Northbridge.
Alpha7125 with Delta 38cfm 60mm screamers (click to hear it, mp3)
The audio is about 10 seconds, starting in front of my face in normal usage position, and moves over in front of
the tower, ending about 6" away from the left side of the case, about even with the lower thermometer.
I thought it was loud before I put the Delta 60mm fans in... yeowzers!

My case temp monitoring rig

This picture was taken with the original Sunon 60mm HO fans. CPU runs about 2-4c cooler with the Deltas.

On Fri, 02 Jun 2000 13:29:55 GMT, David M. wrote in alt.comp.hardware.overclocking:

>Get a radio shack electronic temp monitor and resolder the thermister
>onto long leads for external use.

I took that a few steps further. It's certainly not "cheap", but is WAY cool.

For an extra $35 or so, order a pack of 10 50k @ 25C thermistors from Digi-Key (part number KC005T-ND. This is the same rating and curve (but much faster response) as the one used in the Radio Shack AUTOMOTIVE indoor/outdoor thermometer (63-1023). I prefer the automotive type to the "home" type because BOTH the indoor and outdoor scales go up to 70c, and these unit look good on a 5.25 drive bay cover. These list for $19.99, and frequently go on sale for $14.99
You'll also need at least 6 radio-control servo connectors. I used an Airtronics type for power and Futaba type for the other two connections, since the other two connections won't KILL anything if they get reversed, but power MUST be power.

Here's what I did:

Install the batteries to turn the units on.
Hit the button on the back to switch reading to "c".
Remove batteries.
Open the case... don't throw the back away! Don't lose the screws!
Discard the plastic button and rubber pad from the C/F switch.
Take two blank 5.25" drive bay covers out of your case.
Cut holes in the bay covers to clear the battery clips, capacitor, and to provide a route for wiring. ONLY drill a hole in the corner by the indoor thermistor on one cover... one will be for ambient, and one will be for case temp. The ambient thermistor shouldn't see internal case air, so don't drill that one.

Take the stock probe leads and cut them at about 2 feet from the thermometers. Attached half of a radio-control servo extension wire to the remaining leads. The other half of the servo extension is connected to the Digi-Key thermistors (two needed) with shrink tubing.
Don't forget that thermistors are sensitive... use a hemostat as a heat sink between the solder joint and the thermistor bead, and in any case, do not heat the joint for longer than 3 seconds... pre-tin the wires from the connector to help.
Of the removed "outdoor" probes, discard one, cut the other to about a foot or so.
On ONE thermometer, remove the stock INDOOR thermistor from the corner of the board. This requires removing the entire board... be VERY careful of the LCD (there are two little inserts at each end that power the backlight), and don't lose the plastic buttons and rubber pads.. perhaps you SHOULD save the parts from the C/F switch in case you lose one... I did, my cat stole it. You CAN throw away the indoor thermistor... the leads are too short to be useful, and the desoldering likely killed it anyways.
The outdoor probe was soldered to the pads that originally held the indoor thermistor. This one will be inserted into the supplied suction cup and mounted to the top of the inside of the case.

You should now have two thermometers, one with a probe hanging from it and a second wire with a servo connector hanging from it. The other should only have a lead with a servo connector hanging from it.
To get even more creative, I carefully cut the traces, leaving a 1/8" gap in the middle of the area where the C/F switch was. I then soldered another servo connector to this area. THIS is connected to wires from my case's unused "sleep" switch, which is a momentary-contact switch. By pressing the sleep switch, I can switch the readout between C and F.

Now, center the back (you kept it, right?) over the INSIDE of the bay cover, and carefully drill TINY holes through the cover and check to see if the faceplate will mount up. Trim any openings as needed.

Here's the REALLY fun part.
I used the computer's 5v power supply lead (red and black), and used a voltage divider network to provide 1.5v to the thermometers. For power plugs, I used radio control servo lead extensions, cut in half. This way, the panels can be removed.
Using one pair of resistors for each thermometer, the voltage divider is set up like this:

Once this is all soldered, you can mount the faceplates to the bay covers with the original screws.

The 27-Ohm resistor dissipates about 1/2 watt in this setup, so it runs warm, but within rating. I hot-glued a '486 fan to the bay cover blowing across the back because I don't like heat building up in a confined area.

Now for the two thermistors that you previously prepped with the servo connectors.
I stuck one on the back of my Voodoo3 card with Radio Shack foam tape.
The other one was epoxied INSIDE of my Alpha in a small hole with the thermistor bead in direct contact with the heatplate of the Athlon directly over the CPU core. It reads about 7c higher than the Gigabyte's CPU monitor, which simply sits between the fins of the HS, and has about 50 cfm flowing over it. I was going to post this under the REALLY REALLY fun heading, but a lot of people really don't want to take a drill to a $50 Alpha, and would prefer to find an easier mounting location for the CPU sensor (however, my method is recommended by AMD).

By pressing the top button once, the thermometers display the highest temps reached. Press it again and they display the lowest, press one more time to return to current.
The bottom button activates the LCD's backlight. I thought about soldering it "on" full time, but this causes the voltage on the voltage divider to drop to 1.3 volts. I use it from time to time without a problem, but if you want them on full-time, I would suggest a conventional regulated 1.5vdc power supply. For as little current as these puppies draw, the voltage divider is fine as I have them wired.

FYI, the rocker switch next to the top thermometer is a high-off-low speed switch for the three case fans (2x120mm and 1x92mm).

Any questions, email me at rlockyer@linkline.com