CAN to fiber: How difficult is it? - Page 1
Forum section: electronics / projects

author: AndersJ
author_rank: Frequent Contributor
timestamp: June 11, 2017, 08:18:03 pm
content: How difficult is it to replace a traditional copper based CAN tranceiver/cable with optical fiber?I'm specifically concerned about how the tranceiver needs to be designedto allow half duplex using one fiber.Other concerns are:- What type of off the shelf fiber and connectors is preferred?- How can the tx and rx diodes share the physical fiber connection without interfering with each other?- Are standard components available that does this?Or put it this way: How would you design a fiber based CAN interface?Any ideas or links to information about this are much appreciated.I don't know where to begin exploring this for me entirely unknown territory.

author: Mr.B
author_rank: Unknown
timestamp: June 11, 2017, 08:26:31 pm
content: I don't know about converting CAN to fibre, but I can help out with one of your questions.Quote from: AndersJ on June 11, 2017, 08:18:03 pmDifferent wavelengths.The *near* end transmits on 1310nm and receives on 1490nm.The *far* end transmits on 1490nm and receives on 1310nm.Have a read up about BiDi at this site:http://www.cables-solutions.com/differences-between-sfp-bidi-sfp-and-compact-sfp.html

author: theatrus
author_rank: Frequent Contributor
timestamp: June 11, 2017, 08:47:21 pm
content: CAN also has dominant/recessive signalling which allows one node to override the bus if it has an address with more zeros (whoever is driving the bus). You'll need to add a framing protocol on top of your fiber in order to determine which end of the transceiver should be driving the bus low and not just replicate the bits straight through (or else you'll even just echo yourself).

author: technix
author_rank: Super Contributor
timestamp: June 12, 2017, 12:19:36 am
content: The best fiber analogy to CAN is single-wavelength PON.

author: aandrew
author_rank: Frequent Contributor
timestamp: June 13, 2017, 01:30:43 am
content: CAN to fiber is trivial. We used Ratioplast POF components (905SE660KR001 and 905EM660KR001) that fed the TXD/RXD end of an MCP2562 CAN PHY. The CANH/CANL side was connected to the CAN bus that was running around the board, and then the STM32 CAN peripheral was connected to that same CAN bus with another MCP2562.As you might have gathered, our fiber CAN network was point-to-point and used two POF "wires".

author: jbb
author_rank: Super Contributor
timestamp: June 13, 2017, 08:43:28 am
content: In principle, there should be a way to use a single fiber for the whole multi-unit bus, with light for dominant bits and dark for recessive bits.But I have no idea how to do that in a useful/reliable way.

author: technix
author_rank: Super Contributor
timestamp: June 13, 2017, 01:19:35 pm
content: Quote from: jbb on June 13, 2017, 08:43:28 amThis is what I am talking about: passive optical network. All fibers are connected using beam splitters.

author: AndersJ
author_rank: Frequent Contributor
timestamp: June 15, 2017, 06:57:41 pm
content: Technix,The concepts you mention are new to me.Please feel free to illustrate the PON koncept with a schematic diagram to show what you mean.

author: matkar
author_rank: Regular Contributor
timestamp: June 15, 2017, 07:59:19 pm
content: He probably means this:https://en.wikipedia.org/wiki/Passive_optical_networkOne question regarding passive optical splitter (I'm too lazy to google). If three nodes are connected, are all three nodes seen by each other? Because if you split the fiber in Y topology surely the light emitted by one of the nodes connected to one of the top branch won't be received by the other top branch. Am I wrong?

author: technix
author_rank: Super Contributor
timestamp: June 16, 2017, 12:28:40 am
content: Quote from: matkar on June 15, 2017, 07:59:19 pmThe root node in the Y-splitter train is simply a mirror that reflects the uplink light back down the PON (if TX and RX are on the same wavelength) or a transceiver module wired into a loopback (if TX and RX uses different wavelengths) The latter solution may be easily achievable using COTS EPON/GPON gear. A CAN over PON network will involve ceil(log(n)/log(2)) beam splitters so a lot of optical glass will be used.