I2C signal and power over long range (10meter cable)
$begingroup$
After some reading/testing I managed to make stable communication between 2 devices using I2C with FTP CAT5 copper twisted pair cable.
- Green wire - SCL
- White/green wire - GND
- Blue wire - SDA
- White/blue wire - GND
GND is connected only at one cable end, I2C bus clock is at 10Khz and I have used 10Kom pullup resistors to VCC
It works well and stable. When I decided to use other 2 pairs of the cable for power (+12V), it stopped working. I tested +12V on one pair GND on the other pair, also +12V/GND on same pair: same result, it stopped working. Whole I2C bus stopped working, other devices attached to it too.
Wonder if I can use same cable or go to safest choice - another cable for power.
power i2c
edited yesterday
Huisman
848111
asked yesterday
user3503519user3503519
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$endgroup$
|
show 5 more comments
$begingroup$
After some reading/testing I managed to make stable communication between 2 devices using I2C with FTP CAT5 copper twisted pair cable.
- Green wire - SCL
- White/green wire - GND
- Blue wire - SDA
- White/blue wire - GND
GND is connected only at one cable end, I2C bus clock is at 10Khz and I have used 10Kom pullup resistors to VCC
It works well and stable. When I decided to use other 2 pairs of the cable for power (+12V), it stopped working. I tested +12V on one pair GND on the other pair, also +12V/GND on same pair: same result, it stopped working. Whole I2C bus stopped working, other devices attached to it too.
Wonder if I can use same cable or go to safest choice - another cable for power.
power i2c
edited yesterday
Huisman
848111
asked yesterday
user3503519user3503519
412
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user3503519 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
3
$begingroup$
Did you check that the power on the receiving side is fine enough? No glitches, no droops... CAT5 cables are quite thin, that is why PoE uses >40 V for power.
$endgroup$
– Vladimir Cravero
yesterday
4
$begingroup$
This is where you need an oscilloscope. Everything else will be (educated) guesswork.
$endgroup$
– pipe
yesterday
1
$begingroup$
I wouldn't twist SDA or SCL with GND because you don't want any capacitance between them. I would twist +12V with GND as you do want capacitance between them. What (return) current does the +12V have? (you might have ground bounce)
$endgroup$
– Huisman
yesterday
4
$begingroup$
GND is connected only at one cable end? Unless I am misunderstanding, that does not sound right.
$endgroup$
– mkeith
yesterday
1
$begingroup$
Did you mean UTP cable? I'm sure it can be used for more protocols than just FTP ;)
$endgroup$
– Andrew Morton
22 hours ago
|
show 5 more comments
$begingroup$
After some reading/testing I managed to make stable communication between 2 devices using I2C with FTP CAT5 copper twisted pair cable.
- Green wire - SCL
- White/green wire - GND
- Blue wire - SDA
- White/blue wire - GND
GND is connected only at one cable end, I2C bus clock is at 10Khz and I have used 10Kom pullup resistors to VCC
It works well and stable. When I decided to use other 2 pairs of the cable for power (+12V), it stopped working. I tested +12V on one pair GND on the other pair, also +12V/GND on same pair: same result, it stopped working. Whole I2C bus stopped working, other devices attached to it too.
Wonder if I can use same cable or go to safest choice - another cable for power.
power i2c
edited yesterday
Huisman
848111
asked yesterday
user3503519user3503519
412
New contributor
user3503519 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
After some reading/testing I managed to make stable communication between 2 devices using I2C with FTP CAT5 copper twisted pair cable.
- Green wire - SCL
- White/green wire - GND
- Blue wire - SDA
- White/blue wire - GND
GND is connected only at one cable end, I2C bus clock is at 10Khz and I have used 10Kom pullup resistors to VCC
It works well and stable. When I decided to use other 2 pairs of the cable for power (+12V), it stopped working. I tested +12V on one pair GND on the other pair, also +12V/GND on same pair: same result, it stopped working. Whole I2C bus stopped working, other devices attached to it too.
Wonder if I can use same cable or go to safest choice - another cable for power.
power i2c
power i2c
edited yesterday
Huisman
848111
asked yesterday
user3503519user3503519
412
New contributor
user3503519 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited yesterday
Huisman
848111
asked yesterday
user3503519user3503519
412
New contributor
user3503519 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited yesterday
Huisman
848111
edited yesterday
Huisman
848111
edited yesterday
Huisman
848111
848111
asked yesterday
user3503519user3503519
412
New contributor
user3503519 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked yesterday
user3503519user3503519
412
asked yesterday
user3503519user3503519
412
412
New contributor
user3503519 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
user3503519 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
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Check out our Code of Conduct.
3
$begingroup$
Did you check that the power on the receiving side is fine enough? No glitches, no droops... CAT5 cables are quite thin, that is why PoE uses >40 V for power.
$endgroup$
– Vladimir Cravero
yesterday
4
$begingroup$
This is where you need an oscilloscope. Everything else will be (educated) guesswork.
$endgroup$
– pipe
yesterday
1
$begingroup$
I wouldn't twist SDA or SCL with GND because you don't want any capacitance between them. I would twist +12V with GND as you do want capacitance between them. What (return) current does the +12V have? (you might have ground bounce)
$endgroup$
– Huisman
yesterday
4
$begingroup$
GND is connected only at one cable end? Unless I am misunderstanding, that does not sound right.
$endgroup$
– mkeith
yesterday
1
$begingroup$
Did you mean UTP cable? I'm sure it can be used for more protocols than just FTP ;)
$endgroup$
– Andrew Morton
22 hours ago
|
show 5 more comments
3
$begingroup$
Did you check that the power on the receiving side is fine enough? No glitches, no droops... CAT5 cables are quite thin, that is why PoE uses >40 V for power.
$endgroup$
– Vladimir Cravero
yesterday
4
$begingroup$
This is where you need an oscilloscope. Everything else will be (educated) guesswork.
$endgroup$
– pipe
yesterday
1
$begingroup$
I wouldn't twist SDA or SCL with GND because you don't want any capacitance between them. I would twist +12V with GND as you do want capacitance between them. What (return) current does the +12V have? (you might have ground bounce)
$endgroup$
– Huisman
yesterday
4
$begingroup$
GND is connected only at one cable end? Unless I am misunderstanding, that does not sound right.
$endgroup$
– mkeith
yesterday
1
$begingroup$
Did you mean UTP cable? I'm sure it can be used for more protocols than just FTP ;)
$endgroup$
– Andrew Morton
22 hours ago
3
3
$begingroup$
Did you check that the power on the receiving side is fine enough? No glitches, no droops... CAT5 cables are quite thin, that is why PoE uses >40 V for power.
$endgroup$
– Vladimir Cravero
yesterday
$begingroup$
Did you check that the power on the receiving side is fine enough? No glitches, no droops... CAT5 cables are quite thin, that is why PoE uses >40 V for power.
$endgroup$
– Vladimir Cravero
yesterday
4
4
$begingroup$
This is where you need an oscilloscope. Everything else will be (educated) guesswork.
$endgroup$
– pipe
yesterday
$begingroup$
This is where you need an oscilloscope. Everything else will be (educated) guesswork.
$endgroup$
– pipe
yesterday
1
1
$begingroup$
I wouldn't twist SDA or SCL with GND because you don't want any capacitance between them. I would twist +12V with GND as you do want capacitance between them. What (return) current does the +12V have? (you might have ground bounce)
$endgroup$
– Huisman
yesterday
$begingroup$
I wouldn't twist SDA or SCL with GND because you don't want any capacitance between them. I would twist +12V with GND as you do want capacitance between them. What (return) current does the +12V have? (you might have ground bounce)
$endgroup$
– Huisman
yesterday
4
4
$begingroup$
GND is connected only at one cable end? Unless I am misunderstanding, that does not sound right.
$endgroup$
– mkeith
yesterday
$begingroup$
GND is connected only at one cable end? Unless I am misunderstanding, that does not sound right.
$endgroup$
– mkeith
yesterday
1
1
$begingroup$
Did you mean UTP cable? I'm sure it can be used for more protocols than just FTP ;)
$endgroup$
– Andrew Morton
22 hours ago
$begingroup$
Did you mean UTP cable? I'm sure it can be used for more protocols than just FTP ;)
$endgroup$
– Andrew Morton
22 hours ago
|
show 5 more comments
3 Answers
3
active
oldest
votes
$begingroup$
Maybe overkill if it was working before, but an option is to use an I2C to Differential converter such as PCA9615, LTC4331, etc. If making the resistors smaller don't work or you need to extend the cable, consider not using I2C directly.
Not only the range will be extended but you will also have better noise immunity.
answered yesterday
Wesley LeeWesley Lee
5,71652241
$endgroup$
1
$begingroup$
Great answer, this is exactly what should be done, but of course it may be a radical change for the OP.
$endgroup$
– Jack Creasey
20 hours ago
$begingroup$
I mean, they are super easy to implement (if compared to moving to RS-485, CAN, etc), but yes compared to changing some resistors it is a radical change.
$endgroup$
– Wesley Lee
18 hours ago
1
$begingroup$
@JackCreasey OP's problem is not just cable capacitance, they seem to suffer from noise on 12V line they have added. Lowering pull-up resistors provides some extra noise immunity, but they can't keep lowering that resistance indefinitely.
$endgroup$
– Dmitry Grigoryev
9 hours ago
$begingroup$
@DmitryGrigoryev Since the OP gave no details I'm not sure how you could suggest that noise was being injected. I agree you can't just keep lowering the termination/pullup ….but the OP is too large by 10:1.
$endgroup$
– Jack Creasey
2 hours ago
add a comment |
$begingroup$
As I noted in a comment, it's hard to debug without an oscilloscope trace, but the first thing that stands out from your question is the 10 kOhm pull-up resistor. This is unusually high for I2C, although it could easily work in many cases.
I would try to lower them to 1 kOhm first, to see if it will affect anything. If it helps, you can gradually make them higher, although doing so will impact your rise-time.
answered yesterday
pipepipe
10.3k42658
$endgroup$
$begingroup$
10 k$Omega$ isn't that big for an I2C bus on 10 kHz, though? (Or should it be 100 kHz OP?)
$endgroup$
– Huisman
yesterday
$begingroup$
@Huisman Two good points. 10 kOhm wouldn't worry me at 10 kHz on a normal PCB but maybe it's not enough over the cable. And 10 kHz is unusual but not crazy unusual I guess.
$endgroup$
– pipe
yesterday
6
$begingroup$
10k Ohm is huge for I2C over any distance. That is the primary problem the OP has.
$endgroup$
– Jack Creasey
yesterday
1
$begingroup$
I guess it is better to split the resistors and use one on each end. 2 pullup-resistors @4.7kΩ, one on each end, should be a better choice than a single 2.2kΩ pullup-resistors.
$endgroup$
– 12431234123412341234123
21 hours ago
$begingroup$
I will try lower the resistors, that is all that make sence for me after all that comments.
$endgroup$
– user3503519
1 hour ago
add a comment |
$begingroup$
You absolutely need to drop your pullup resistors at long distances, and 10m is a long way and 10k Ohm is very high.
The value of the pullup resistor is related to three things:
- Cable capacitance
- Aiming voltage and Rx level sense.
- Speed
Try using any of the available calculators and start your reading here with the TI appnote on pullup values or here with the NXP I2C standard (7.1).
In terms of the problem you are having, it should be obvious that grounding additional pairs (12V,Gnd) in the cable will change the capacitance to the I2C signal wires.
answered yesterday
Jack CreaseyJack Creasey
14.9k2823
$endgroup$
2
$begingroup$
I agree, CAT5 cable can be assumed to have about 50pF per meter so 10 meters exceed the 400pF capacitance limit of I2C specification. And reaching 400kHz I2C clock can't be achieved with 400pF capacitance by using the specified 3mA pull-up current from resistors. Fortunately, slowing speed down will help - unless the devices have a minimum clock speed limitation. We don't know what devices these are and what is the I2C bus voltages but indeed pullups should be adjusted to provide at least 3mA and if devices allow and agree on the bus low level voltage then even more.
$endgroup$
– Justme
22 hours ago
$begingroup$
Yes I gonna test with that, but my question is why it work if there is not power over that cable?
$endgroup$
– user3503519
1 hour ago
$begingroup$
A floating cable pair does not have the same capacitance to your signal pair that it has when the cable is grounded. For your configuration both the +12 and the Gnd are essentially the same ….they have capacitance to the signal cable that impacts your risetime. .
$endgroup$
– Jack Creasey
56 mins ago
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
Maybe overkill if it was working before, but an option is to use an I2C to Differential converter such as PCA9615, LTC4331, etc. If making the resistors smaller don't work or you need to extend the cable, consider not using I2C directly.
Not only the range will be extended but you will also have better noise immunity.
answered yesterday
Wesley LeeWesley Lee
5,71652241
$endgroup$
1
$begingroup$
Great answer, this is exactly what should be done, but of course it may be a radical change for the OP.
$endgroup$
– Jack Creasey
20 hours ago
$begingroup$
I mean, they are super easy to implement (if compared to moving to RS-485, CAN, etc), but yes compared to changing some resistors it is a radical change.
$endgroup$
– Wesley Lee
18 hours ago
1
$begingroup$
@JackCreasey OP's problem is not just cable capacitance, they seem to suffer from noise on 12V line they have added. Lowering pull-up resistors provides some extra noise immunity, but they can't keep lowering that resistance indefinitely.
$endgroup$
– Dmitry Grigoryev
9 hours ago
$begingroup$
@DmitryGrigoryev Since the OP gave no details I'm not sure how you could suggest that noise was being injected. I agree you can't just keep lowering the termination/pullup ….but the OP is too large by 10:1.
$endgroup$
– Jack Creasey
2 hours ago
add a comment |
$begingroup$
Maybe overkill if it was working before, but an option is to use an I2C to Differential converter such as PCA9615, LTC4331, etc. If making the resistors smaller don't work or you need to extend the cable, consider not using I2C directly.
Not only the range will be extended but you will also have better noise immunity.
answered yesterday
Wesley LeeWesley Lee
5,71652241
$endgroup$
1
$begingroup$
Great answer, this is exactly what should be done, but of course it may be a radical change for the OP.
$endgroup$
– Jack Creasey
20 hours ago
$begingroup$
I mean, they are super easy to implement (if compared to moving to RS-485, CAN, etc), but yes compared to changing some resistors it is a radical change.
$endgroup$
– Wesley Lee
18 hours ago
1
$begingroup$
@JackCreasey OP's problem is not just cable capacitance, they seem to suffer from noise on 12V line they have added. Lowering pull-up resistors provides some extra noise immunity, but they can't keep lowering that resistance indefinitely.
$endgroup$
– Dmitry Grigoryev
9 hours ago
$begingroup$
@DmitryGrigoryev Since the OP gave no details I'm not sure how you could suggest that noise was being injected. I agree you can't just keep lowering the termination/pullup ….but the OP is too large by 10:1.
$endgroup$
– Jack Creasey
2 hours ago
add a comment |
$begingroup$
Maybe overkill if it was working before, but an option is to use an I2C to Differential converter such as PCA9615, LTC4331, etc. If making the resistors smaller don't work or you need to extend the cable, consider not using I2C directly.
Not only the range will be extended but you will also have better noise immunity.
answered yesterday
Wesley LeeWesley Lee
5,71652241
$endgroup$
Maybe overkill if it was working before, but an option is to use an I2C to Differential converter such as PCA9615, LTC4331, etc. If making the resistors smaller don't work or you need to extend the cable, consider not using I2C directly.
Not only the range will be extended but you will also have better noise immunity.
answered yesterday
Wesley LeeWesley Lee
5,71652241
answered yesterday
Wesley LeeWesley Lee
5,71652241
answered yesterday
Wesley LeeWesley Lee
5,71652241
answered yesterday
Wesley LeeWesley Lee
5,71652241
5,71652241
1
$begingroup$
Great answer, this is exactly what should be done, but of course it may be a radical change for the OP.
$endgroup$
– Jack Creasey
20 hours ago
$begingroup$
I mean, they are super easy to implement (if compared to moving to RS-485, CAN, etc), but yes compared to changing some resistors it is a radical change.
$endgroup$
– Wesley Lee
18 hours ago
1
$begingroup$
@JackCreasey OP's problem is not just cable capacitance, they seem to suffer from noise on 12V line they have added. Lowering pull-up resistors provides some extra noise immunity, but they can't keep lowering that resistance indefinitely.
$endgroup$
– Dmitry Grigoryev
9 hours ago
$begingroup$
@DmitryGrigoryev Since the OP gave no details I'm not sure how you could suggest that noise was being injected. I agree you can't just keep lowering the termination/pullup ….but the OP is too large by 10:1.
$endgroup$
– Jack Creasey
2 hours ago
add a comment |
1
$begingroup$
Great answer, this is exactly what should be done, but of course it may be a radical change for the OP.
$endgroup$
– Jack Creasey
20 hours ago
$begingroup$
I mean, they are super easy to implement (if compared to moving to RS-485, CAN, etc), but yes compared to changing some resistors it is a radical change.
$endgroup$
– Wesley Lee
18 hours ago
1
$begingroup$
@JackCreasey OP's problem is not just cable capacitance, they seem to suffer from noise on 12V line they have added. Lowering pull-up resistors provides some extra noise immunity, but they can't keep lowering that resistance indefinitely.
$endgroup$
– Dmitry Grigoryev
9 hours ago
$begingroup$
@DmitryGrigoryev Since the OP gave no details I'm not sure how you could suggest that noise was being injected. I agree you can't just keep lowering the termination/pullup ….but the OP is too large by 10:1.
$endgroup$
– Jack Creasey
2 hours ago
1
1
$begingroup$
Great answer, this is exactly what should be done, but of course it may be a radical change for the OP.
$endgroup$
– Jack Creasey
20 hours ago
$begingroup$
Great answer, this is exactly what should be done, but of course it may be a radical change for the OP.
$endgroup$
– Jack Creasey
20 hours ago
$begingroup$
I mean, they are super easy to implement (if compared to moving to RS-485, CAN, etc), but yes compared to changing some resistors it is a radical change.
$endgroup$
– Wesley Lee
18 hours ago
$begingroup$
I mean, they are super easy to implement (if compared to moving to RS-485, CAN, etc), but yes compared to changing some resistors it is a radical change.
$endgroup$
– Wesley Lee
18 hours ago
1
1
$begingroup$
@JackCreasey OP's problem is not just cable capacitance, they seem to suffer from noise on 12V line they have added. Lowering pull-up resistors provides some extra noise immunity, but they can't keep lowering that resistance indefinitely.
$endgroup$
– Dmitry Grigoryev
9 hours ago
$begingroup$
@JackCreasey OP's problem is not just cable capacitance, they seem to suffer from noise on 12V line they have added. Lowering pull-up resistors provides some extra noise immunity, but they can't keep lowering that resistance indefinitely.
$endgroup$
– Dmitry Grigoryev
9 hours ago
$begingroup$
@DmitryGrigoryev Since the OP gave no details I'm not sure how you could suggest that noise was being injected. I agree you can't just keep lowering the termination/pullup ….but the OP is too large by 10:1.
$endgroup$
– Jack Creasey
2 hours ago
$begingroup$
@DmitryGrigoryev Since the OP gave no details I'm not sure how you could suggest that noise was being injected. I agree you can't just keep lowering the termination/pullup ….but the OP is too large by 10:1.
$endgroup$
– Jack Creasey
2 hours ago
add a comment |
$begingroup$
As I noted in a comment, it's hard to debug without an oscilloscope trace, but the first thing that stands out from your question is the 10 kOhm pull-up resistor. This is unusually high for I2C, although it could easily work in many cases.
I would try to lower them to 1 kOhm first, to see if it will affect anything. If it helps, you can gradually make them higher, although doing so will impact your rise-time.
answered yesterday
pipepipe
10.3k42658
$endgroup$
$begingroup$
10 k$Omega$ isn't that big for an I2C bus on 10 kHz, though? (Or should it be 100 kHz OP?)
$endgroup$
– Huisman
yesterday
$begingroup$
@Huisman Two good points. 10 kOhm wouldn't worry me at 10 kHz on a normal PCB but maybe it's not enough over the cable. And 10 kHz is unusual but not crazy unusual I guess.
$endgroup$
– pipe
yesterday
6
$begingroup$
10k Ohm is huge for I2C over any distance. That is the primary problem the OP has.
$endgroup$
– Jack Creasey
yesterday
1
$begingroup$
I guess it is better to split the resistors and use one on each end. 2 pullup-resistors @4.7kΩ, one on each end, should be a better choice than a single 2.2kΩ pullup-resistors.
$endgroup$
– 12431234123412341234123
21 hours ago
$begingroup$
I will try lower the resistors, that is all that make sence for me after all that comments.
$endgroup$
– user3503519
1 hour ago
add a comment |
$begingroup$
As I noted in a comment, it's hard to debug without an oscilloscope trace, but the first thing that stands out from your question is the 10 kOhm pull-up resistor. This is unusually high for I2C, although it could easily work in many cases.
I would try to lower them to 1 kOhm first, to see if it will affect anything. If it helps, you can gradually make them higher, although doing so will impact your rise-time.
answered yesterday
pipepipe
10.3k42658
$endgroup$
$begingroup$
10 k$Omega$ isn't that big for an I2C bus on 10 kHz, though? (Or should it be 100 kHz OP?)
$endgroup$
– Huisman
yesterday
$begingroup$
@Huisman Two good points. 10 kOhm wouldn't worry me at 10 kHz on a normal PCB but maybe it's not enough over the cable. And 10 kHz is unusual but not crazy unusual I guess.
$endgroup$
– pipe
yesterday
6
$begingroup$
10k Ohm is huge for I2C over any distance. That is the primary problem the OP has.
$endgroup$
– Jack Creasey
yesterday
1
$begingroup$
I guess it is better to split the resistors and use one on each end. 2 pullup-resistors @4.7kΩ, one on each end, should be a better choice than a single 2.2kΩ pullup-resistors.
$endgroup$
– 12431234123412341234123
21 hours ago
$begingroup$
I will try lower the resistors, that is all that make sence for me after all that comments.
$endgroup$
– user3503519
1 hour ago
add a comment |
$begingroup$
As I noted in a comment, it's hard to debug without an oscilloscope trace, but the first thing that stands out from your question is the 10 kOhm pull-up resistor. This is unusually high for I2C, although it could easily work in many cases.
I would try to lower them to 1 kOhm first, to see if it will affect anything. If it helps, you can gradually make them higher, although doing so will impact your rise-time.
answered yesterday
pipepipe
10.3k42658
$endgroup$
As I noted in a comment, it's hard to debug without an oscilloscope trace, but the first thing that stands out from your question is the 10 kOhm pull-up resistor. This is unusually high for I2C, although it could easily work in many cases.
I would try to lower them to 1 kOhm first, to see if it will affect anything. If it helps, you can gradually make them higher, although doing so will impact your rise-time.
answered yesterday
pipepipe
10.3k42658
edited yesterday
answered yesterday
pipepipe
10.3k42658
answered yesterday
pipepipe
10.3k42658
answered yesterday
pipepipe
10.3k42658
10.3k42658
$begingroup$
10 k$Omega$ isn't that big for an I2C bus on 10 kHz, though? (Or should it be 100 kHz OP?)
$endgroup$
– Huisman
yesterday
$begingroup$
@Huisman Two good points. 10 kOhm wouldn't worry me at 10 kHz on a normal PCB but maybe it's not enough over the cable. And 10 kHz is unusual but not crazy unusual I guess.
$endgroup$
– pipe
yesterday
6
$begingroup$
10k Ohm is huge for I2C over any distance. That is the primary problem the OP has.
$endgroup$
– Jack Creasey
yesterday
1
$begingroup$
I guess it is better to split the resistors and use one on each end. 2 pullup-resistors @4.7kΩ, one on each end, should be a better choice than a single 2.2kΩ pullup-resistors.
$endgroup$
– 12431234123412341234123
21 hours ago
$begingroup$
I will try lower the resistors, that is all that make sence for me after all that comments.
$endgroup$
– user3503519
1 hour ago
add a comment |
$begingroup$
10 k$Omega$ isn't that big for an I2C bus on 10 kHz, though? (Or should it be 100 kHz OP?)
$endgroup$
– Huisman
yesterday
$begingroup$
@Huisman Two good points. 10 kOhm wouldn't worry me at 10 kHz on a normal PCB but maybe it's not enough over the cable. And 10 kHz is unusual but not crazy unusual I guess.
$endgroup$
– pipe
yesterday
6
$begingroup$
10k Ohm is huge for I2C over any distance. That is the primary problem the OP has.
$endgroup$
– Jack Creasey
yesterday
1
$begingroup$
I guess it is better to split the resistors and use one on each end. 2 pullup-resistors @4.7kΩ, one on each end, should be a better choice than a single 2.2kΩ pullup-resistors.
$endgroup$
– 12431234123412341234123
21 hours ago
$begingroup$
I will try lower the resistors, that is all that make sence for me after all that comments.
$endgroup$
– user3503519
1 hour ago
$begingroup$
10 k$Omega$ isn't that big for an I2C bus on 10 kHz, though? (Or should it be 100 kHz OP?)
$endgroup$
– Huisman
yesterday
$begingroup$
10 k$Omega$ isn't that big for an I2C bus on 10 kHz, though? (Or should it be 100 kHz OP?)
$endgroup$
– Huisman
yesterday
$begingroup$
@Huisman Two good points. 10 kOhm wouldn't worry me at 10 kHz on a normal PCB but maybe it's not enough over the cable. And 10 kHz is unusual but not crazy unusual I guess.
$endgroup$
– pipe
yesterday
$begingroup$
@Huisman Two good points. 10 kOhm wouldn't worry me at 10 kHz on a normal PCB but maybe it's not enough over the cable. And 10 kHz is unusual but not crazy unusual I guess.
$endgroup$
– pipe
yesterday
6
6
$begingroup$
10k Ohm is huge for I2C over any distance. That is the primary problem the OP has.
$endgroup$
– Jack Creasey
yesterday
$begingroup$
10k Ohm is huge for I2C over any distance. That is the primary problem the OP has.
$endgroup$
– Jack Creasey
yesterday
1
1
$begingroup$
I guess it is better to split the resistors and use one on each end. 2 pullup-resistors @4.7kΩ, one on each end, should be a better choice than a single 2.2kΩ pullup-resistors.
$endgroup$
– 12431234123412341234123
21 hours ago
$begingroup$
I guess it is better to split the resistors and use one on each end. 2 pullup-resistors @4.7kΩ, one on each end, should be a better choice than a single 2.2kΩ pullup-resistors.
$endgroup$
– 12431234123412341234123
21 hours ago
$begingroup$
I will try lower the resistors, that is all that make sence for me after all that comments.
$endgroup$
– user3503519
1 hour ago
$begingroup$
I will try lower the resistors, that is all that make sence for me after all that comments.
$endgroup$
– user3503519
1 hour ago
add a comment |
$begingroup$
You absolutely need to drop your pullup resistors at long distances, and 10m is a long way and 10k Ohm is very high.
The value of the pullup resistor is related to three things:
- Cable capacitance
- Aiming voltage and Rx level sense.
- Speed
Try using any of the available calculators and start your reading here with the TI appnote on pullup values or here with the NXP I2C standard (7.1).
In terms of the problem you are having, it should be obvious that grounding additional pairs (12V,Gnd) in the cable will change the capacitance to the I2C signal wires.
answered yesterday
Jack CreaseyJack Creasey
14.9k2823
$endgroup$
2
$begingroup$
I agree, CAT5 cable can be assumed to have about 50pF per meter so 10 meters exceed the 400pF capacitance limit of I2C specification. And reaching 400kHz I2C clock can't be achieved with 400pF capacitance by using the specified 3mA pull-up current from resistors. Fortunately, slowing speed down will help - unless the devices have a minimum clock speed limitation. We don't know what devices these are and what is the I2C bus voltages but indeed pullups should be adjusted to provide at least 3mA and if devices allow and agree on the bus low level voltage then even more.
$endgroup$
– Justme
22 hours ago
$begingroup$
Yes I gonna test with that, but my question is why it work if there is not power over that cable?
$endgroup$
– user3503519
1 hour ago
$begingroup$
A floating cable pair does not have the same capacitance to your signal pair that it has when the cable is grounded. For your configuration both the +12 and the Gnd are essentially the same ….they have capacitance to the signal cable that impacts your risetime. .
$endgroup$
– Jack Creasey
56 mins ago
add a comment |
$begingroup$
You absolutely need to drop your pullup resistors at long distances, and 10m is a long way and 10k Ohm is very high.
The value of the pullup resistor is related to three things:
- Cable capacitance
- Aiming voltage and Rx level sense.
- Speed
Try using any of the available calculators and start your reading here with the TI appnote on pullup values or here with the NXP I2C standard (7.1).
In terms of the problem you are having, it should be obvious that grounding additional pairs (12V,Gnd) in the cable will change the capacitance to the I2C signal wires.
answered yesterday
Jack CreaseyJack Creasey
14.9k2823
$endgroup$
2
$begingroup$
I agree, CAT5 cable can be assumed to have about 50pF per meter so 10 meters exceed the 400pF capacitance limit of I2C specification. And reaching 400kHz I2C clock can't be achieved with 400pF capacitance by using the specified 3mA pull-up current from resistors. Fortunately, slowing speed down will help - unless the devices have a minimum clock speed limitation. We don't know what devices these are and what is the I2C bus voltages but indeed pullups should be adjusted to provide at least 3mA and if devices allow and agree on the bus low level voltage then even more.
$endgroup$
– Justme
22 hours ago
$begingroup$
Yes I gonna test with that, but my question is why it work if there is not power over that cable?
$endgroup$
– user3503519
1 hour ago
$begingroup$
A floating cable pair does not have the same capacitance to your signal pair that it has when the cable is grounded. For your configuration both the +12 and the Gnd are essentially the same ….they have capacitance to the signal cable that impacts your risetime. .
$endgroup$
– Jack Creasey
56 mins ago
add a comment |
$begingroup$
You absolutely need to drop your pullup resistors at long distances, and 10m is a long way and 10k Ohm is very high.
The value of the pullup resistor is related to three things:
- Cable capacitance
- Aiming voltage and Rx level sense.
- Speed
Try using any of the available calculators and start your reading here with the TI appnote on pullup values or here with the NXP I2C standard (7.1).
In terms of the problem you are having, it should be obvious that grounding additional pairs (12V,Gnd) in the cable will change the capacitance to the I2C signal wires.
answered yesterday
Jack CreaseyJack Creasey
14.9k2823
$endgroup$
You absolutely need to drop your pullup resistors at long distances, and 10m is a long way and 10k Ohm is very high.
The value of the pullup resistor is related to three things:
- Cable capacitance
- Aiming voltage and Rx level sense.
- Speed
Try using any of the available calculators and start your reading here with the TI appnote on pullup values or here with the NXP I2C standard (7.1).
In terms of the problem you are having, it should be obvious that grounding additional pairs (12V,Gnd) in the cable will change the capacitance to the I2C signal wires.
answered yesterday
Jack CreaseyJack Creasey
14.9k2823
edited 21 hours ago
answered yesterday
Jack CreaseyJack Creasey
14.9k2823
answered yesterday
Jack CreaseyJack Creasey
14.9k2823
answered yesterday
Jack CreaseyJack Creasey
14.9k2823
14.9k2823
2
$begingroup$
I agree, CAT5 cable can be assumed to have about 50pF per meter so 10 meters exceed the 400pF capacitance limit of I2C specification. And reaching 400kHz I2C clock can't be achieved with 400pF capacitance by using the specified 3mA pull-up current from resistors. Fortunately, slowing speed down will help - unless the devices have a minimum clock speed limitation. We don't know what devices these are and what is the I2C bus voltages but indeed pullups should be adjusted to provide at least 3mA and if devices allow and agree on the bus low level voltage then even more.
$endgroup$
– Justme
22 hours ago
$begingroup$
Yes I gonna test with that, but my question is why it work if there is not power over that cable?
$endgroup$
– user3503519
1 hour ago
$begingroup$
A floating cable pair does not have the same capacitance to your signal pair that it has when the cable is grounded. For your configuration both the +12 and the Gnd are essentially the same ….they have capacitance to the signal cable that impacts your risetime. .
$endgroup$
– Jack Creasey
56 mins ago
add a comment |
2
$begingroup$
I agree, CAT5 cable can be assumed to have about 50pF per meter so 10 meters exceed the 400pF capacitance limit of I2C specification. And reaching 400kHz I2C clock can't be achieved with 400pF capacitance by using the specified 3mA pull-up current from resistors. Fortunately, slowing speed down will help - unless the devices have a minimum clock speed limitation. We don't know what devices these are and what is the I2C bus voltages but indeed pullups should be adjusted to provide at least 3mA and if devices allow and agree on the bus low level voltage then even more.
$endgroup$
– Justme
22 hours ago
$begingroup$
Yes I gonna test with that, but my question is why it work if there is not power over that cable?
$endgroup$
– user3503519
1 hour ago
$begingroup$
A floating cable pair does not have the same capacitance to your signal pair that it has when the cable is grounded. For your configuration both the +12 and the Gnd are essentially the same ….they have capacitance to the signal cable that impacts your risetime. .
$endgroup$
– Jack Creasey
56 mins ago
2
2
$begingroup$
I agree, CAT5 cable can be assumed to have about 50pF per meter so 10 meters exceed the 400pF capacitance limit of I2C specification. And reaching 400kHz I2C clock can't be achieved with 400pF capacitance by using the specified 3mA pull-up current from resistors. Fortunately, slowing speed down will help - unless the devices have a minimum clock speed limitation. We don't know what devices these are and what is the I2C bus voltages but indeed pullups should be adjusted to provide at least 3mA and if devices allow and agree on the bus low level voltage then even more.
$endgroup$
– Justme
22 hours ago
$begingroup$
I agree, CAT5 cable can be assumed to have about 50pF per meter so 10 meters exceed the 400pF capacitance limit of I2C specification. And reaching 400kHz I2C clock can't be achieved with 400pF capacitance by using the specified 3mA pull-up current from resistors. Fortunately, slowing speed down will help - unless the devices have a minimum clock speed limitation. We don't know what devices these are and what is the I2C bus voltages but indeed pullups should be adjusted to provide at least 3mA and if devices allow and agree on the bus low level voltage then even more.
$endgroup$
– Justme
22 hours ago
$begingroup$
Yes I gonna test with that, but my question is why it work if there is not power over that cable?
$endgroup$
– user3503519
1 hour ago
$begingroup$
Yes I gonna test with that, but my question is why it work if there is not power over that cable?
$endgroup$
– user3503519
1 hour ago
$begingroup$
A floating cable pair does not have the same capacitance to your signal pair that it has when the cable is grounded. For your configuration both the +12 and the Gnd are essentially the same ….they have capacitance to the signal cable that impacts your risetime. .
$endgroup$
– Jack Creasey
56 mins ago
$begingroup$
A floating cable pair does not have the same capacitance to your signal pair that it has when the cable is grounded. For your configuration both the +12 and the Gnd are essentially the same ….they have capacitance to the signal cable that impacts your risetime. .
$endgroup$
– Jack Creasey
56 mins ago
add a comment |
user3503519 is a new contributor. Be nice, and check out our Code of Conduct.
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3
$begingroup$
Did you check that the power on the receiving side is fine enough? No glitches, no droops... CAT5 cables are quite thin, that is why PoE uses >40 V for power.
$endgroup$
– Vladimir Cravero
yesterday
4
$begingroup$
This is where you need an oscilloscope. Everything else will be (educated) guesswork.
$endgroup$
– pipe
yesterday
1
$begingroup$
I wouldn't twist SDA or SCL with GND because you don't want any capacitance between them. I would twist +12V with GND as you do want capacitance between them. What (return) current does the +12V have? (you might have ground bounce)
$endgroup$
– Huisman
yesterday
4
$begingroup$
GND is connected only at one cable end? Unless I am misunderstanding, that does not sound right.
$endgroup$
– mkeith
yesterday
1
$begingroup$
Did you mean UTP cable? I'm sure it can be used for more protocols than just FTP ;)
$endgroup$
– Andrew Morton
22 hours ago