[caption id="attachment_1181" align="aligncenter" width="540"]!(http://alternet.us.com/wp-content/uploads/2011/03/digital- wiring-2.jpg) Digital wiring harnesses[/caption]
I'd had some trouble with the digital wiring for the analyzer. I made the first set of harnesses using this horrible orange wire that kept coiling-up. Because every wire was the same color, it was a nightmare. Also, at the time, I was diagnosing a problem with the PLO1 and PLO3 modules. It had appeared that the control signals for the PLO modules weren't very clean. In an attempt to addresses both these issues, I decided to redo all the digital wiring. While wandering around my almost-local electronics store (i <3 norvac) I came across this twisted-pair ribbon cable.
[caption id="attachment_1182" align="aligncenter" width="540"]!(http://alternet.us.com/wp-content/uploads/2011/03/digital- wiring-3.jpg) Twisted-pair ribbon cable[/caption]
The idea behind using twisted-pair cable is that you should always match a current-return path to every signal. The paired wire provides that path. The return current helps to cancel and isolate the electromagnetic field created by the forward current.
[caption id="attachment_1183" align="aligncenter" width="540"]!(http://alternet.us.com/wp-content/uploads/2011/03/digital- wiring-4.jpg) Removing wiring from backing[/caption]
To build the harness, I removed each pair from its plastic backing. I built a few without removing the plastic, and it worked. I prefer to remove it, if possible, however.
[caption id="attachment_1184" align="aligncenter" width="540"]!(http://alternet.us.com/wp-content/uploads/2011/03/digital- wiring-5.jpg) Solder the ground wires together[/caption]
At the module-end of the harness strip and solder the ground wires together. Solder some additional wire to the bundle to include in the connector.
[caption id="attachment_1185" align="aligncenter" width="540"]!(http://alternet.us.com/wp-content/uploads/2011/03/digital- wiring-6.jpg) Connectorize and shrink-wrap[/caption]
After crimping connectors to each wire, attach the header and begin to prepare the sheathing. I put shrink-wrap over the ground wires. To install the plastic sheathing, first slide shrink-wrap over the bundle all the way to the connector end, then slide the sheathing down. Carefully slip the shrink-wrap over the loose-end of the sheath and shrink.
[caption id="attachment_1188" align="aligncenter" width="540"]!(http://alternet.us.com/wp-content/uploads/2011/03/digital- wiring-9.jpg) Control board side[/caption]
The control board side of the harness is built after the sheath is installed. Like before, strip and combine the ground wires, and connectorize all of them. This time, however, there isn't a single connector for the harness, so you simply need to add them to each of the existing connectors on the control board.
[caption id="attachment_1187" align="aligncenter" width="540"]!(http://alternet.us.com/wp-content/uploads/2011/03/digital- wiring-8.jpg) Completed module harness[/caption]
This is what the finished harness connector looks like installed (yes, I know it's too long, but it's all I had available).
[caption id="attachment_1189" align="aligncenter" width="540"]!(http://alternet.us.com/wp-content/uploads/2011/03/digital- wiring-10.jpg) Control board side of wiring harnesses[/caption]
On the control board side there is unavoidable chaos. Each of the individual harnesses for each module ends and its signal wires simple terminate wherever they're needed. The interesting thing to note is that, because I color-coded the signals, you can plainly see the type of signal that each wire carries. For example, the purple wires in the foreground are the data signals for each serial control connection to the modules. Just behind it are many white wires that carry the Latch-enable of FQUD signals.
So far, I'm pretty happy with the new cables. I think they are easier to manage and look good. Also, the signals appear very clean when I view them on the 'scope.