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Simple portable Ethernet port tester - does this really not exist?

Ambious
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You can't have very simple and cheap ethernet port testers because you basically need to have an ethernet card connected to the port, and have that card send some data and receive data back from the switch or from the ethernet card on the other end.

 

You don't just have some voltage on the pins in the ethernet jack, ethernet uses pairs of wires and you need a tiny transformer on each pair of wires for isolation purposes, so the signal on wires is not continuous, it's pulses of electricity.

 

The cable testers you can buy cheaply online work in a totally different way... the end piece simply has some resistors or some transistors and leds (dumb side) and the main piece sends continuous DC voltage through each wire and on the other end if the voltage comes through the wire then you know that wire is connected properly in the ethernet cable.  These testers are just for testing if the wires are properly crimped in the ethernet jacks, they can't tell you if you have an ethernet card or a switch at the other end.

 

You could make something in the form of a usb stick with a microcontroller , a cheap ethernet controller IC and jack with magnetics built-in but the total BOM would cost you 5-10$ at least. 

 

A raspberri pi could be something cheap, you could write some code that would light up a led when the ethernet card receives an IP from a switch through dhcp or something, so when you plug the pi into the functional port

 

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So the University I go to has a pretty shitty wifi. The wired Ethernet ports are super fast because nobody uses them, but a lot of them are inactive.

I'm tired of going port by port with my laptop and connecting it to test, so I figured - why not just find a simple link tester and use that?

Except... Those don't exist?

I only found pretty expensive and big testing tools - is there not a tool that's just an RJ45 male jack with a couple of leds that blink if there's a link in that port and don't if there isn't? Something thumb-sized to put on your keyring?

If such a thing doesn't exist, would it be very complicated to make one, do you think?

Thanks!

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Try making one yourself, just connect and LED to some of the wires of a known working Ethernet port and see if you get any blinks or anything.

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3 minutes ago, Theguywhobea said:

Try making one yourself, just connect and LED to some of the wires of a known working Ethernet port and see if you get any blinks or anything.

It does sound like it could be a fun and simple project, and I have access to a lab with the right equipment, but I'd rather buy something preexisting if such a thing exists. I think I might just be searching using the wrong terms.

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Just now, Ambious said:

It does sound like it could be a fun and simple project, and I have access to a lab with the right equipment, but I'd rather buy something preexisting if such a thing exists. I think I might just be searching using the wrong terms.

You should first try making it instead of buying one, especially if you have access to the right equipment. You might learn something neat!

Desktop: i9 11900k, 32GB DDR4, 4060 Ti 8GB 🙂

 

 

 

 

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Such a device does exist, but it appears to be hard to find (as an example: https://www.amazon.com/Smartronix-Linkcheck-Ethernet-Tester/dp/B000RGI6R6) Other testers I've seen just test whether or not the cable is physically good or something, but not if any actual network is on it.

 

You could also find USB powered hubs/switches and power it with a battery bank.

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3 minutes ago, M.Yurizaki said:

Such a device does exist, but it appears to be hard to find (as an example: https://www.amazon.com/Smartronix-Linkcheck-Ethernet-Tester/dp/B000RGI6R6) Other testers I've seen just test whether or not the cable is physically good or something, but not if any actual network is on it.

 

You could also find USB powered hubs/switches and power it with a battery bank.

That's a good place to start. Thanks!

 

ETA: Yikes, dat price.

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They are easy to find. Just google RJ45 Loopback Tester

If you're interested in a product please download and read the manual first.

Don't forget to tag or quote in your reply if you want me to know you've answered or have another question.

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1 hour ago, keskparane said:

They are easy to find. Just google RJ45 Loopback Tester

I'm pretty sure those only light up the leds in the router, so it's useless if you don't have access to that.

I could be wrong, but I don't think that itself has any leds on it.

I should note the sockets don't have leds either.

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You can't have very simple and cheap ethernet port testers because you basically need to have an ethernet card connected to the port, and have that card send some data and receive data back from the switch or from the ethernet card on the other end.

 

You don't just have some voltage on the pins in the ethernet jack, ethernet uses pairs of wires and you need a tiny transformer on each pair of wires for isolation purposes, so the signal on wires is not continuous, it's pulses of electricity.

 

The cable testers you can buy cheaply online work in a totally different way... the end piece simply has some resistors or some transistors and leds (dumb side) and the main piece sends continuous DC voltage through each wire and on the other end if the voltage comes through the wire then you know that wire is connected properly in the ethernet cable.  These testers are just for testing if the wires are properly crimped in the ethernet jacks, they can't tell you if you have an ethernet card or a switch at the other end.

 

You could make something in the form of a usb stick with a microcontroller , a cheap ethernet controller IC and jack with magnetics built-in but the total BOM would cost you 5-10$ at least. 

 

A raspberri pi could be something cheap, you could write some code that would light up a led when the ethernet card receives an IP from a switch through dhcp or something, so when you plug the pi into the functional port

 

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https://www.amazon.com/Networx-Gigabit-RJ45-Loopback-Tester/dp/B00E4OKGDE/ref=pd_sbs_147_1/141-5179444-3080047?_encoding=UTF8&pd_rd_i=B00E4OKGDE&pd_rd_r=CHC1F6X2A9T4JC5JJ5B1&pd_rd_w=ptGv6&pd_rd_wg=fbPgP&psc=1&refRID=CHC1F6X2A9T4JC5JJ5B1

 

Insanity is not the absence of sanity, but the willingness to ignore it for a purpose. Chaos is the result of this choice. I relish in both.

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@Jtalk4456 and others  ... he wants something to plug into ports in his classroom or whatever and see right there if the other end of the cable is connected to a switch somewhere in the building or if the actual connector is working (has no pins bent, broken, nobody stepped on the cable until it's screwed etc)

 

Those loopback things don't give any visual indicator that the port works, and he can't go to the server room to see if the led on some port is now turned on ... he wouldn't even know which of the tens to hundreds of leds would even belong to the port he tests if he can access the switches.

 

 

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2 minutes ago, mariushm said:

@Jtalk4456 and others  ... he wants something to plug into ports in his classroom or whatever and see right there if the other end of the cable is connected to a switch somewhere in the building or if the actual connector is working (has no pins bent, broken, nobody stepped on the cable until it's screwed etc)

 

Those loopback things don't give any visual indicator that the port works, and he can't go to the server room to see if the led on some port is now turned on ... he wouldn't even know which of the tens to hundreds of leds would even belong to the port he tests if he can access the switches.

 

 

ok that makes sense, but if you're going to every port and testing, then I would suggest using the computer as the tester instead of spending time testing then plugging in. A tester will not save him that much time. he'll have to then unplug it and plug the computer in anyways. Once he finds out what ports are good, use those ports every time. If he really wants to save time, he should make a list or put a sticker on the problematic plugs and submit that to the it department to be switched out so people don't waste their time trying to figure out what plug is good

Insanity is not the absence of sanity, but the willingness to ignore it for a purpose. Chaos is the result of this choice. I relish in both.

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6 hours ago, Ambious said:

I'm pretty sure those only light up the leds in the router, so it's useless if you don't have access to that.

I could be wrong, but I don't think that itself has any leds on it.

I should note the sockets don't have leds either.

You're correct. The description I first read didn't make it clear to me that the LED's were not in the device itself.

If you're interested in a product please download and read the manual first.

Don't forget to tag or quote in your reply if you want me to know you've answered or have another question.

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15 hours ago, mariushm said:

You can't have very simple and cheap ethernet port testers because you basically need to have an ethernet card connected to the port, and have that card send some data and receive data back from the switch or from the ethernet card on the other end.

 

You don't just have some voltage on the pins in the ethernet jack, ethernet uses pairs of wires and you need a tiny transformer on each pair of wires for isolation purposes, so the signal on wires is not continuous, it's pulses of electricity.

 

The cable testers you can buy cheaply online work in a totally different way... the end piece simply has some resistors or some transistors and leds (dumb side) and the main piece sends continuous DC voltage through each wire and on the other end if the voltage comes through the wire then you know that wire is connected properly in the ethernet cable.  These testers are just for testing if the wires are properly crimped in the ethernet jacks, they can't tell you if you have an ethernet card or a switch at the other end.

 

You could make something in the form of a usb stick with a microcontroller , a cheap ethernet controller IC and jack with magnetics built-in but the total BOM would cost you 5-10$ at least. 

 

A raspberri pi could be something cheap, you could write some code that would light up a led when the ethernet card receives an IP from a switch through dhcp or something, so when you plug the pi into the functional port

 

Ah, thanks, that sheds a lot light on the issue I've been missing.

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