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Can I use the load module with the CT-3 for cable resistance (Bypass C-C)?

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发表于: 20-08-2021 07:22:31
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Is it possible to use the load module (SM-LD-00) with the CT-3 cable resistance (Bypass C-C) test?  It doesn't appear to work.

The Bypass (C-C) test requires a load on the female USB-A power but it would be nice to use the load module instead.

(I know that I can use the Bypass Load-Free function but I'd like to use a 5A load for testing cable quality)

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发表于: 20-08-2021 14:27:41
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I just built myself an add-on board for my CT-3 to test the quality (resistance) of USB cables - it will do A-mini, A-micro, A-C and C-C cables. I also thought that using the internal load would be nice, but having a load resistor on my board makes more sense as it's at the "far end" of the cable allowing a true 4-wire test to be carried out (I'm using DP & DM to detect voltage drop across the Vbus & ground lines). I'm going to write a Lua script which will detect when a cable is plugged in, prompt for cable length from a list, then, once the button on the board is pressed for a second or 2, will cause the cable to be graded from 1 (garbage) to 5 (fantastic).. Here's a link to some photos and schematic: https://drive.google.com/drive/f ... DDh0zao?usp=sharing
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发表于: 24-08-2021 19:18:58
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Unfortunately nope.

The meter controls the load current to meet the target value.

However, the way the bypass method work is the fact that the current going through the meter is bypassed by a certain amount along with the cable, and the meter compares the current before and after the plug-in of the cable and gives the result.

You can see there is a conflict, you cannot adjust the load module's current with a partially bypassed current sensing resistor.
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