Details about electrons moving in a wire, --interesting Youtube video Options

[Dave_Darling]

Very very tangential relevance to 914s, but if you ever wanted to know details about electrical flow in your electrical system...

This video focuses on what happens when you have one pair of wires connected to another pair in a Y configuration, but it also contains information on how electrons flow through a circuit--


https://www.youtube.com/watch?v=2AXv49dDQJw


It's very neat to watch the visualization of the "wave" of voltage (and similar wave of current flow) that propagates down the wire. The way he set up the measurement is very complicated, but the results are awesome.

--DD

[Superhawk996]

Automotive CAN bus principle and why the bus lines have to be terminated properly.

Typical CAN termination resistor is 120 ohms. Only two termination resistors can be used. Measuring across the CAN high and CAN low wire you should see 60 ohms (two 120 ohm resistors in parallel = 60 ohms).

When adding additional CAN modules, if the new module has an unexpected termination resistor, it will screw up the whole CAN bus. Can’t tell you how many times I’ve seen this problem occur on prototype vehicles.

Likewise, if one of the modules that contains the 120 ohm termination resistor dies catastrophically or its termination resistance is removed from the bus there will be communication problems.

Whenever I’m trying to trouble shoot a flaky CAN issue, 1st step is to measure across the high/low lines looking for the proper 60 ohms.


The joys and nightmares of modern vehicles where CAN has become ubiquitous.