Matthew PeverillThe idea with the shield was to host the analog multiplexers and some of the lamp test electronics, as well as to break down the pin connections in to logically sensible headers. The schematic is on github. Here's the board:
The connector in the top left is the one I'm trying to test. In order from right to left the pins are: Vcc, Gnd, A5 (SCL), A4 (SDA).
Continuity tests on the board show those pins connecting to the relevant headers, and not to each other. My i2c device works fine if I plug it directly in to my arduino, but it fails if I plug it in to the ports in my shield. So what could else could be going wrong? It's the cables - the extra long female to female jcp cables I ordered from aliexpress are nearly all completely useless. When I hooked it up with a 6" cable it works fine. Lesson learned - now I just need a different source for 20" female to female ribbon cables :(
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It does seem to be connectivity. If I strip out wire pairs that don't connect, I was eventually able to get the an adafruit device to run off my shield. There is some different problem with the connection to the next board, apparently.
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Hmm good idea. I plugged the cables in to a cable testing rig. It looks to me like every fourth cable pair actually isn't connected at all. The 6" cable doesn't have this problem, so I think it is DC connectivity. I hope capacitance isn't an issue, because I'm going to need some kind of 20" cable eventually and I'm not sure what I'd do about that.
Are you sure? yes | no
Is there DC connectivity on the faulty cable? Could it be the extra capacitance of the long cable is loading down the clock and data lines?
Are you sure? yes | no