Hello,
I am part of an undergraduate research team designing a sensor array.
Our remote modules require 5.3V and ~100mA at 75m (ideally driven with ~6V at the source). The design uses I2C with the P82B96 for data. This will require a pair of wires (SDA, SCL) with a capacitance no greater than 52pF/m and 15V ~10mA to run the data transmission and the P82B96.
What configuration(s) work with these requirements (with undergrad budget constraints), and what connectors would be best?
Welcome to the forum.
I strongly advise you not to use I2C for a 75 meter long communication link.
I2C was originally explicitly designed for communication on a single PCB, not for wired systems.
It has been very crudely adapted to work in wired applications with extra driver ICs but it is a horrible compromise that very often leads to intermittent reliability issues causing data loss or corruption.
Instead I recombined you use one of the many communications standards designed specifically for long wire communication. TIA-232-F is a very low cost and easy to use standard but many other standards exist which are tailored for specific wiring environments.
Thank you for your reply-
At this point in the project it is not practical to change the protocol we’re using. We will rely on the P82B96P, a lower data speed, and wire with controlled capacitance to mitigate the issues with this method.
With these restrictions, what kind of cable(s) and connectors could work for this application?
Ada,
That is a little difficult to answer for a few reasons. First, you’d have to break out the part to some kind of board and then attach a header connector to said board. Paul is correct that I2C was designed for shorter lengths and isolated boards. If you had to stick with the cable method, you’d have to use some kind of wire that had shielding on it to prevent further signal integrity degradation. Even so, I’m not sure the signal would make it all the way, 75 meters is a long way to go for a slower signal. Some initial research shows that a twisted pair cable might be okay, and maybe even some ethernet cables rated at CAT5 or CAT6. As to how you implement it, that is up to you on how to accomplish this. You really would have to break out to some kind of board first, in my opinion. Probably not ideal to go with a simple breadboard either, you’d have to have a PCB. This may involve looking into our PCB Builder too.
Hello @Ada,
Welcome to the TechForum!
I’m glad to see you thinking about the balanced transmission lines associated with the P82B96P. This table from the datasheet suggests your design should work, provided we lower our serial clock expectations from MHz to kHz.
As for cable, I’d start with CAT 5 or CAT 6. The best undergrad-budget-friendly cable is whatever the school’s IT department can spare. The characteristic impedance is about 100 Ω. You may need to experiment with termination resistors.
Please let know if you were successful. I’d love to see a picture of your project.
Sincerely,
Aaron
