PSAS/ news/ 2005-12-06 - First meeting of the capstone team: Introductions, USB vs. CAN, and EagleCAD

Attending: Sarah Bailey, GlennLeBrasseur, Jacob Davidson, Andrew Greenberg, and various other PSAS members.

Project Brainstorming (Requirements, etc.)


For USB, the host always asks for data (nodes can't transmit unless the host polls them). USB may or may not have the priority transmission scheme that CAN has (i.e. in CAN, the node with the lowest ID number has the highest priority and will transmit before other nodes). *AI* Find RealTime applications of USB (like automotive applications) - use Compendex from PSU library page. Applications articles would be a good source to see how other people dealt with the priority issues.

Andrew says, even with isochronous transfers, the host must still initiate the transfer. Bart claims the host controller hides the polling for data. Andrew claims the lowest protocol layer might get to us. Bart says you can avoid some of the "plug & play" issues by having a static USB setup. Greg Kroah-Hartman is the Linux USB guy (we might be able to set up a meeting with him). Is the latency specified to microseconds or milliseconds? Is there a data frame packer delay across device?

Andrew says CAN has the properties of a "fly by wire" system. Bosch replaced CAN by FlexRay, which is also a "fly by wire" system.

Is there a "CAN in a nutshell" document? Andrew says there are CAN bus links to documents (I've linked them from the Capstone homepage).

We should decide whether we're doing USB or CAN or both by early January (since we have have a project proposal by the end of January).

EagleCAD demo

Old CAN nodes are in subversion (EagleCAD files). EagleCAD is an open source layout tool. There is a free version and a paid version. The free version will do most things, although neither version will do four-layer boards. EagleCAD does do automatic place and route, but you should do it manually first. is the official EagleCAD website.

Random Notes

You can buy a USB to CAN converter.

Should the HAP be a part of every CAN node? It's not necessary for all nodes, so why should we make each node bigger than it has to be? Other nodes may only need a smaller battery or a super capacitor.

Could have SPI (serial peripheral interface) to connect to other nodes.

18 volt power from the CAN bus, have to convert to a smaller voltage. Arm cores have 1.8 volts, but they use 3.3 volts for I/O.

Replacements for EagleCAD?

XPCB is another open source tool, but it doesn't have a schematic capture. You could, however, generate a netlist from another tool (like Saber). We'd like to stick with one tool though.

Next Meeting

Scheduled for December 13th (7pm, Andrew's cabin). "Official" Capstone meeting with Professor Faust December 16th, 11am, in FAB 160-16. Also meeting scheduled for December 20th, 7pm, probably in FAB 155.

Official meeting agenda: Capstone members should come with a list of questions. The sponsor will explain the project, and minions (oops, team members) should ferret out deliverables, objectives, goals, and schedules.

Workshop for EagleCAD coming soon. PARTS was talking about doing a workshop, we should try to coordinate with them.

If we decide to do USB, we can ask questions and/or set up an appointment with Greg Kroah-Hartman.