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Single ended signal transmission (lemmy.world)

submitted 5 days ago by TelepathicWalrus@lemmy.world to c/askelectronics@discuss.tchncs.de

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Hi,

I am thinking about the best way to transmit 5 single ended signals from one board to another as well as ground and 2 power rails. I was thinking cat5e cable with a standard rj45 plug but as cat5e is twisted pair I'm concerned about crosstalk.

The cable between the two boards would be a maximum of 50cm. 3 of the signals are addresses for a multiplexer that would change at a maximum speed of 2ms per change. One of the other signals is a 20khz pwm signal. The final signal is a zc detector for mains so max Freq of 100/120hz.

There may be high current switches at ac line frequency (50/60hz) near by.

Would single ended transmission with cat5e cable be okay for this or would I need differential signalling? If I need differential signalling, what sort of cable/connector could I use?

Any help is appreciated

Thanks

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[–] dgriffith@aussie.zone 4 points 5 days ago (1 children)

The cable between the two boards would be a maximum of 50cm. 3 of the signals are addresses for a multiplexer that would change at a maximum speed of 2ms per change. One of the other signals is a 20khz pwm signal. The final signal is a zc detector for mains so max Freq of 100/120hz.

None of this will be a problem over 50cm of cat5. If you were talking about millivolt or MHz signalling then you'd have to be a bit more careful.

[–] TelepathicWalrus@lemmy.world 1 points 5 days ago

Thank you for your response. I was hoping to run the power (3.3v and 24v) through the same cat5e cable. They wouldn't be high current, probably 100ma max. Do you think this would be ok too?

Thanks

[–] hmn@lemmy.staphup.nl 1 points 4 days ago* (last edited 4 days ago) (1 children)

Hi there,

i'm quite new to all of this, but i found this guy who has soem interesting info regarding grouding/coupling in designs.

Because you said any help is appreciated, maybe you're interested. Basically Hans Rosenberg has a 4 part yt lecture as a teaser to his free 9 part minicourse. His free minicourse is "Module 1" of his paid full course.

In his 4 part teaser he also throws in an example for digital signals

[–] TelepathicWalrus@lemmy.world 1 points 20 hours ago

Oh thanks, I'll check it out 👍

[–] BigDanishGuy@sh.itjust.works 1 points 5 days ago (1 children)

If you're designing for production then talk with the assembly guys, they will have options and cost estimates.

If we're talking a one of, then just try. It's only 500mm so not that much can happen. Especially at the slow speeds you mentioned. 20kHz isn't that fast compared to the +100MHz that a cat5e is designed for when using differential signalling.

Are plugs a must? If not I'd consider soldering the wires. At least for testing the cable's suitability.

If you must use plugs, then don't use rj45. Some yahoo, like yours truly, will come along and go "neat, an undocumented ethernet capability" and fry something expensive. Have a look around DigiKey or where you get your parts, and find a less common plug.

And if you end up needing more wires, then get an old parallel ATA HDD cable from the early 2000s. They have 80 wires and are free at the dump.

[–] TelepathicWalrus@lemmy.world 1 points 5 days ago

I like the use of the rj45 because it is cheap, easy to assemble and reliable. The plugs won't be accessible to the end user unless they open up the device so hopfully they won't fry anything.

Ultimately I will just have to try and see what works and what doesn't.

Thank you for your reply 😊