Cool!
Oh yeah, your articles were the first ones that I read every month (I probably still have a few "Circuit Craft" magazines lying around). You have a knack for making electronics easy to understand (try "The Art of Electronics" for a taste of the other end of the spectrum). LadyAda of Adafruit.com (Limor Fried), Jeremy Blum (jeremyblum.com), and of course Jeri Ellsworth (all over Youtube) are the current generation's best (IMHO) at making electronics accessible.
As you probably know, impedance-matched terminations should help if the problem is noise.
They do. DeviceNet specs a 121 ohm terminating resistor, I found some precision 60.5 ohm resistors on Digikey and got a few k of them. To go with the resistors, I also bought 22 nf caps that we wired to the center point of the resistors (the resistors being wired in series to get us the original 121 ohms). The other end of the cap is tied to ground (not shield).
This should give us 3db in noise reduction. That's definitely helpful, and not to be sneezed at. But the cables that our benevolent corporate overloads foisted upon us contains not only the DeviceNet conductors, but 110VAC power conductors as well. You might ask "what were they thinking?" The simple answer is, they weren't. You should see the scope traces... Ugly. :O
And the cables that we use are the top of the line "Control Boss" made by Sine/Amphenol (no longer being made by all appearances), which despite their gold-plated contacts regularly build up a few ohms of resistance (and a few is all that it takes), which takes the network down.
And since DeviceNet carries its power in the same cable as its data lines (although it doesn't have to), voltage drop becomes a serious problem long before we run up to the max length of the network. We are currently trying out these:
http://www.ebay.com/itm/251379658717?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 to boost the voltage at the far ends of the network. Initial results have been very good, and at $6 you aren't going to lose much. You can actually get them cheaper, but they appear to be a cheap knockoff of a product that is already coming out of China (notice how the wires wound around the ferrite core are touching their neighbors. I'll pass on these).
S, anyways, the other day I was (re)reading a bit of "Serial Port Complete" and lamenting the zero slew rate of the transceiver chips. I had toyed with the idea of popping out the ones that I could get to and putting in newer/better ones. Then I thought, why not just add a RC network to each transmit and receive line and create my own slew?
Am I missing something obvious?
