Hi everyone,
I have recently been using a SHT40 humidity sensor (https://www.adafruit.com/product/4885) with your i2c extender LTC4311 (https://www.adafruit.com/product/4756) and this works GREAT with a 30m CAT5e cable, as explained by Collin's lab tutorial (https://www.youtube.com/watch?v=AFRwKN-7NbM)
However, the same LTC4311 cannot reach 30m with the NAU7802. It works with a 10m CAT5e cable but at 30m it doesn't. It tries to connect, outputs a word or two and then jams.
I was surprised because I am under the impression that they use the same protocol and libraries. What am I missing?
I did not fool around with I2C clock speed but I could not verify if NAU7802 sample code defaults to 100kHz. Clock speed doesn't seem to be mentioned in the source code (.h, .cpp).
Any help will be appreciated.
Thank you, Have a great day!
Fred
NAU7802: I2C extender at 30m CAT5e
Moderators: adafruit_support_bill, adafruit
Please be positive and constructive with your questions and comments.
- adafruit_support_bill
- Posts: 88152
- Joined: Sat Feb 07, 2009 10:11 am
Re: NAU7802: I2C extender at 30m CAT5e
Have you verified that it works with a short distance direct connection?
- frederic_t3e
- Posts: 18
- Joined: Fri Apr 15, 2016 4:23 pm
Re: NAU7802: I2C extender at 30m CAT5e
Hi Bill,
well the "NAU7802 + I2C extender + 10m CAT5e + Arduino " works.
(I use the Ethernet socket adapter: https://www.adafruit.com/product/4981)
Do you mean I should test "NAU7802 + 10cm hookup wires + Arduino"?
I can but since the 10m setup worked, I assumed...
Fred
well the "NAU7802 + I2C extender + 10m CAT5e + Arduino " works.
(I use the Ethernet socket adapter: https://www.adafruit.com/product/4981)
Do you mean I should test "NAU7802 + 10cm hookup wires + Arduino"?
I can but since the 10m setup worked, I assumed...
Fred
- adafruit_support_bill
- Posts: 88152
- Joined: Sat Feb 07, 2009 10:11 am
Re: NAU7802: I2C extender at 30m CAT5e
30m is 3 time as long and has 3 time as much bulk capacitance as 10m. 3 times the capacitance means that the driver circuitry on the chip needs to work 3 times harder to produce a crisp waveform. Most likely, the NAU7802 drive circuitry is just not as strong as that used on the SHT40.
You can try moving the active terminator to the other end of the cable to see if that works better.
You can try moving the active terminator to the other end of the cable to see if that works better.
- frederic_t3e
- Posts: 18
- Joined: Fri Apr 15, 2016 4:23 pm
Re: NAU7802: I2C extender at 30m CAT5e
Thank you for your answer, Bill! I did not think about the drive circuit strength nor moving the I2C extender. The other end did not work for the SHT40 but I will try it with the NAU7802 anyway. Also, would it help to have two LTC4311 in a row?
I will also try 20m cable, since this is my real requirement for the NAU7802. I just had the 30m cable lying around and could not understand why it could work for one chip and not the other. Maybe the drive circuit is weaker but can sustain 20m.
Thanks a lot,
Fred
I will also try 20m cable, since this is my real requirement for the NAU7802. I just had the 30m cable lying around and could not understand why it could work for one chip and not the other. Maybe the drive circuit is weaker but can sustain 20m.
Thanks a lot,
Fred
- adafruit_support_bill
- Posts: 88152
- Joined: Sat Feb 07, 2009 10:11 am
Re: NAU7802: I2C extender at 30m CAT5e
I'm not sure that multiple LTC4311s would help. The LTC4311 acts as an active pullup to improve the shape of the rising edge of the signal compared to what can be achieved with passive pullup resistors alone.
The falling edge of the signal is driven by whichever device is actively communicating on the bus. If you have access to an oscilloscope, you should be able to see what those signals actually look like on the bus.
The falling edge of the signal is driven by whichever device is actively communicating on the bus. If you have access to an oscilloscope, you should be able to see what those signals actually look like on the bus.
- frederic_t3e
- Posts: 18
- Joined: Fri Apr 15, 2016 4:23 pm
Re: NAU7802: I2C extender at 30m CAT5e
Hi again Bill,
Yes, you are right multiple LTC4311 did not help.
I increased progressively the cable length up to 17m and it worked. I am still waiting for some ethernet cable to test more lengths and find the maximum length tolerated. That's why I did not answer sooner.
Unfortunately, I do not have access to an oscilloscope, although I have turned my Arduino into a rough oscilloscope in the past. I might have a look eventually.
Will give you the final results when I'm done with the various lengths.
Thanks,
Fred
Yes, you are right multiple LTC4311 did not help.
I increased progressively the cable length up to 17m and it worked. I am still waiting for some ethernet cable to test more lengths and find the maximum length tolerated. That's why I did not answer sooner.
Unfortunately, I do not have access to an oscilloscope, although I have turned my Arduino into a rough oscilloscope in the past. I might have a look eventually.
Will give you the final results when I'm done with the various lengths.
Thanks,
Fred
- frederic_t3e
- Posts: 18
- Joined: Fri Apr 15, 2016 4:23 pm
Re: NAU7802: I2C extender at 30m CAT5e
Hi again,
I got my cable yesterday. With the i2c extender, the signal is still loud and clear at 20m. So somewhere between 20 and 30m, the capacitance becomes excessive. Fortunately, 20m is enough for this project.
If anyone ever finds a way to reach 30m with the NAU7802, please contact me.
Have a good day,
Fred
I got my cable yesterday. With the i2c extender, the signal is still loud and clear at 20m. So somewhere between 20 and 30m, the capacitance becomes excessive. Fortunately, 20m is enough for this project.
If anyone ever finds a way to reach 30m with the NAU7802, please contact me.
Have a good day,
Fred
- adafruit_support_bill
- Posts: 88152
- Joined: Sat Feb 07, 2009 10:11 am
Re: NAU7802: I2C extender at 30m CAT5e
Thanks for posting your results. :)
Please be positive and constructive with your questions and comments.