How much distance can dc signal travel in cat6 cable?

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I am using atmega32 to control two dc motors,my question is what is the max distance of cat6 cable that I can go with between the controller and the motor driver.I just want to send the rotation direction signal just high or low.

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This is one of those bit "It Depends" things...  It depends on two things: 

 

(1) How much current?

 

(2) What is the "speed" (e.g. bit rate, frequency, square wave vs sine wave, etc)?

 

If this is just a logical control signal (e.g. not motor power) and not something faster like a fast PWM, then the answer may be "as far as you want". Try it on a spool of CAT6, if you have access to the inside end of the wire. This will be a worst case and it will probably work there.

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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Yes it is just a logical control signal, thanks for the answer.

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is what is the max distance

 

Need more information.

 

Recall that "back in the olden times" telegraph systems worked for miles over one and two wire systems.

(That was, essentially, low speed digital signaling)

 

As the length of the wire, and hence its dc resistance and its capacitance increases, the relative cost for a specialized driver and receiver becomes immaterial in the overall system cost.

 

JC 

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WEll CAT6 is rated for 250MHz so I think your logic levels are within spec.  Cat6 is also 23 gauge so unless you are pulling a couple amps @5v I think a 1000 foot spool should do just fine.

 

East Side Jim

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Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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That's perfect for me! Thank you

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How are you sending the signal? Any length of wire becomes an antenna, so there’s a chance your signal may get corrupted. Common solutions would be rs485/422 or current loop.

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What interface are you using?
I.e I2C, SPI, Usart, rs232/422/485

Cause not all communications methods will work at long distance, like I2C.

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I just want to send a logical signal not a data packet.

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Even so, interference can upset the signal. This might cause the motor to run in the wrong direction.

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A current loop is less susceptible to interference. A certain meteorological company uses a current loop to simultaneously power up to 4 wind speed and direction sensors located around airports and collect their data at total distances of in excess of 4 miles! Current loops work!

Ross McKenzie ValuSoft Melbourne Australia

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Kartman wrote:
How are you sending the signal? Any length of wire becomes an antenna, so there’s a chance your signal may get corrupted. Common solutions would be rs485/422 or current loop.

 

Kartman wrote:

Even so, interference can upset the signal. This might cause the motor to run in the wrong direction.

 

True, but as we have seen here in the past, as long as the pin driving the line stays active...meaning high, or low, it should not be a big issue.  Driving 1000 feet could be an issue if the line sits on top of lighting fixtures and such, but as the OP states, its not data packets either. 

 

Maybe the OP can provide a little more insight as to distance he/she wants to go with these signal(s).

 

JIm

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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... and a 4-20mA current loop covers the open circuit loop issue also.

Ross McKenzie ValuSoft Melbourne Australia

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The common stepper motor driver modules use current loop. Rs422 or current loop are common methods in cnc machine tools.

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In theory, a DC signal can go many miles, given the nearly 0 current drawn by a modern digital input.
In reality, you have to start worrying about such long wires starting to act like antennas, and picking up noise and stray signals that become bigger than the drive capability of the digital pin...

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I'd use RF modules. Cheaper than all that wire and a lot easier to string.

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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The current loop advise is well reasoned.  Proven way to send logic signals over miles of copper.

 

One key thing to watch for, and a good argument for current loop is ground shift or offset.  I did some work many years ago on a private school campus where they tried to run differential RS-422 from building to building.  The AC grounds between the buildings differed by as much as 25V AC.  The RS-422 receivers couldn't handle the common mode AC signal and it was a mess.  A whole bunch of expensive isolators fixed it, but beware of this issue on long runs.

 

Current loop doesn't use a ground reference at the far end so it doesn't have this problem.  If you use just simple DC levels instead make sure your receive end can handle a reasonably large common mode voltage.

 

Filter the heck out of the signal at the receiver too.  You will pick up noise so you want to reject anything faster than the signal you are trying to send.

 

Dave

 

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lundquist wrote:

Current loop doesn't use a ground reference at the far end...

 

Nor does RS422/RS485; it's the voltage difference between the two lines that defines the logic level.

 

And surely a current loop will also suffer from common mode problems unless the receiver/sensor is totally line powered and isolated from anything else.?

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

Last Edited: Sun. May 26, 2019 - 01:59 PM
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Brian Fairchild wrote:

lundquist wrote:

Current loop doesn't use a ground reference at the far end...

 

Nor does RS422/RS485; it's the voltage difference between the two lines that defines the logic level.

 

And surely a current loop will also suffer from common mode problems unless the receiver/sensor is totally line powered and isolated from anything else.?

 

The problem is if you take your statement about RS422/485 at it's face value.  Yes, it is a differential receiver, but the standard receivers have very limited common mode range.  Some as little as +/- 7V.  That can easily be overwhelmed by ground differences over a short distance.   There are newer parts that have enhanced common mode range but it is an issue that needs to be managed.

 

By current loop, I assumed properly implemented such as the copper loop telephone subscriber circuit where the far end is fully floating.  Usually optical or transformer coupled.

 

Dave

 

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I'd put an opto isolator on the receiving end just to be sure there is no common mode problem.

 

But then, I'd likely just use RF to go that distance anyhow.

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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Have in mind that for current loop 19.2K baud is about max speed for any distance where  RS422/485 is 1M baud + at same distance.

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sparrow2 wrote:
Have in mind that for current loop 19.2K baud is about max speed for any distance where  RS422/485 is 1M baud + at same distance.

 

The OP says the signal is just the rotation direction of a motor, high or low. So I'm guessing the signal has a frequency of a few Hz, tops.

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the signal has a frequency of a few Hz, tops.

just want to send the rotation direction signal just high or low.

It seems that it's just DC, without the hurts ...  winkso all that is required is Ohms law to work out the maximum distance.

 

Hey but of course this is a freak's site, could the answer be just THAT SIMPLE? And I notice no mention of whether the signal is generated in Assembler, C, C++ or other, that would surely come into the mix. devil

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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js wrote:

Hey but of course this is a freak's site, could the answer be just THAT SIMPLE?

 

I already have an idea to complicate it. Using the current loop, but instead of terminating with an optocoupler, _two_ optocouplers can be used, with inverse polarities from each other (charlieplexing style):

 

 

This way, D0/D1 can be HI/LO or LO/HI to rotate the motor in each direction (each combination will activate a different optocoupler). To stop the motor, LO/LO or HI/HI (both optocouplers off). In other words, you can set the motor in 3 states with a single twisted pair cable.

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Has anyone noticed the OP has gone silent(or just ran away) after post #9?

 

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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jgmdesign wrote:

Has anyone noticed the OP has gone silent(or just ran away) after post #9?

 

Jim

He got the answer he was looking for and unsubscribed

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Kuch wrote:
He got the answer he was looking for and unsubscribed
His account is still ACTIVE... but yes he may never return... well maybe when he has another problem that needs a solution.

Ross McKenzie ValuSoft Melbourne Australia