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Trying to figure out how ethernet cable tester works

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
A thought: https://www.maximintegrated.com/en/products/power/protection-control/protection-ics/MAX14672.html

I have no idea. For every pin?

POE and telco are high voltages too.

Maybe a voltmeter to scan the pairs or take the pairs and full bridge them and detect a voltage >1 V before usng the tester. Suggesting building a potential verifier.
e.g. Take pin 1 &2; full wave rectify and check for a voltage >3V. Do the same for the other pairs. Ya know like an outlet tester.

Again, I have no idea: https://www.commsgroup.com/poe-power-over-ethernet-tester--checker-xt401-
 

throbscottle

Well-Known Member
Not forgetting it's only protecting a chip worth about 40 pence!
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
Not forgetting it's only protecting a chip worth about 40 pence!
True, but waiting for the boat from China is a long time when you need one.


1623446768998.png

pic is from the video.

I think figureing out HOW to protect the device is a really challenging problem.

What if you replaced all of the LED''s with a 3 terminal bi-color LED and LT3092 current sources and/or that maxim device or a surge stopper from analog devices?

Ground isn't shown on that schematic.
 

throbscottle

Well-Known Member
Er.... right. That's just going to be building a whole new tester.

Anyway, the boat from China isn't an issue. I can get many parts next day delivery from RadioSpares.

So, the good news is, I fixed it! Chopped off the IC leads which drove the outputs, soldered a SMD MC14017 onto 2 bits of FFC cable, cunningly with some bits folded round the back to connect CE to Vss and Q9 to reset (it drives 8 lines + shield), wrapped it up in Koptan tape (cheaper than Kapton!), split the FFC into individual conductors, threaded them through the original IC leg holes (which I had to enlarge slightly), peeled back the insulation and soldered them in. I connected the clock pin to the tester's "heartbeat" LED, turned it on and watched the lights race along at high speed!

Turns out there is a control pulse or 2 in that LED's supply, triggering the counter extra times. So feeding the counter via a diode going into a 20k and 4n7 in parallel stopped the funny business. Now seeing 2 LEDs have failed on the main unit! Grrr. Replaced them. Working, yay!

Well OK not quite working. It's all operated by one tactile switch, which is connected to the heartbeat LED. Auto works fine and that's the main thing. Manual mode I can get with a bit of fiddling. But it won't turn off now so I have to disconnect the battery. Which is fine because it's what I had been doing anyway to stop it getting turned on by accident and draining it. Maybe I'll get round to changing the 20k and 4n7 to some value which lets it work properly but still stops the counter going crazy...
 
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