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Groth · 06-09-2003, 06:22 AM

Do-able, indeed. Actually, the whole thing was fairly easy.

For ye olde K6, I paralleled 5 generic 0.1 Ohm, 3% resistors. For the upcoming KX7 project, I have ten resistors from the same company (Ohmite), but I've chosen the 10 series for their higher precision. Their temp-co isn't as nice the nichrome, so they'll need a fan when doing important work. Depending on what I find when I pull the inductors, I'll use 6 or 9 for the sensing.

A length of twisted pair was attached to the shunt and led to the amplifier stage. I used a TI LF412 dual JFET-input op-amp, half as a unity gain difference amp, half as an inverting amp with a gain of 21. For the Abit board's turn, I'll add another LF412, so that I have 3 difference amps, one for each inductor, and an inverting summing amp with a gain of 75-80 or 110-120.

Next is the isolation stage. I didn't want the reading/recording of date to affect the target computer's workload, so the I passed the amp stage output and a Vcore reading through a pair of ISO124 isolation amplifiers.

Last, but not least, the isolated signals were digitized with a Nat Semi LM87. I used it because it is noise tolerant, easy to interface, and supported by Motherboard Monitor. It only has 8 bit resolution (around 0.2 A resolution for the K7's), but, I already had one in the house.

New brake rotors first; schematics soon.

06-09-2003, 06:22 AM	#94
Groth Cooling Savant Join Date: Mar 2003 Location: MO Posts: 781	Do-able, indeed. Actually, the whole thing was fairly easy. For ye olde K6, I paralleled 5 generic 0.1 Ohm, 3% resistors. For the upcoming KX7 project, I have ten resistors from the same company (Ohmite), but I've chosen the 10 series for their higher precision. Their temp-co isn't as nice the nichrome, so they'll need a fan when doing important work. Depending on what I find when I pull the inductors, I'll use 6 or 9 for the sensing. A length of twisted pair was attached to the shunt and led to the amplifier stage. I used a TI LF412 dual JFET-input op-amp, half as a unity gain difference amp, half as an inverting amp with a gain of 21. For the Abit board's turn, I'll add another LF412, so that I have 3 difference amps, one for each inductor, and an inverting summing amp with a gain of 75-80 or 110-120. Next is the isolation stage. I didn't want the reading/recording of date to affect the target computer's workload, so the I passed the amp stage output and a Vcore reading through a pair of ISO124 isolation amplifiers. Last, but not least, the isolated signals were digitized with a Nat Semi LM87. I used it because it is noise tolerant, easy to interface, and supported by Motherboard Monitor. It only has 8 bit resolution (around 0.2 A resolution for the K7's), but, I already had one in the house. New brake rotors first; schematics soon.