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Jul 28, 2012 at 3:24 answer added Chris Stratton timeline score: 4
Jul 27, 2012 at 20:45 comment added The Photon @Peter, my first thought was "he can probably use a snubber"... but then I realized you'd given so little information and some things were non-physical as described so I didn't feel safe giving that answer...For future questions, please try to give us some help to help you, and you'll be more likely to get a good answer in a shorter time.
Jul 27, 2012 at 20:15 comment added markrages Can you take a picture of your scope probe connected to the circuit?
Jul 27, 2012 at 19:59 vote accept Peter
Jul 27, 2012 at 19:59 answer added Peter timeline score: 2
Jul 27, 2012 at 19:42 comment added Peter @ThePhoton I can't open up the cable and there is no documentation on it. I am assuming it is a 26AWG wire bundle. Definitely not coax or ribbon.
Jul 27, 2012 at 19:42 comment added Peter @stevenvh I will post a few pics. I thought about it last night and I have a 'good enough' solution at the moment, but I'd like to understand the underlying issue.
Jul 26, 2012 at 5:52 comment added stevenvh I don't expect a higher RC will be the solution, I just want to see what's needed to get some effect. (service message: I like "Steven" better than "@stevenvh", but you'll have to write the latter, otherwise I won't get notified of your comment. I don't have to write "@Peter" because you'll get notified anyway since it's your question.)
Jul 25, 2012 at 19:56 comment added Oli Glaser How many SPI ICs are there on the board side? Have you tested to see if the spikes are present on the PCI side without the cable/board connected? Have you tried just using a series resistance rather than the RC filter? (i.e. no C) Also answering Photon's questions would definitely help to get to the bottom of this.
Jul 25, 2012 at 18:44 comment added Nick Alexeev app note on the subject: Extending the SPI bus for long-distance communication.
Jul 25, 2012 at 16:47 comment added Saad You could add resistor and two schottkys at the receiver. The schottky will clip the voltage at Vcc+Vf - where Vf is the forward voltage drop of the diode.
Jul 25, 2012 at 16:35 history tweeted twitter.com/#!/StackElectronix/status/228166653924478977
Jul 25, 2012 at 16:29 comment added Peter Steven: I have not and that is something I was planning on looking at next, but I don't think that will be the final solution. It surprised me that I saw no noticeable drop in spike when I put the RC in. I approximated 40nS spike as equal to 25Mhz (1/40ns) so I would have expected at least a 20dB drop. I am now speculating that perhaps inductance in the return line is mitigating the capacitor? That's why I was thinking of just sticking at IC buffer/zener on the lines. But that seems like a bazooka to kill a fly approach. ;)
Jul 25, 2012 at 16:19 comment added The Photon Is the cable ribbon cable? coax? twisted-pair? What are the wire sizes? Does it have equal number of signal and ground wires? What's the arrangement of signal relative to ground wires? When you observed the 12 V overshoot, how and where were you probing your circuit? What was the duration of the overshoot? Was there equal undershoot on falling edges? Can you post a schematic of your receiving circuit?
Jul 25, 2012 at 16:15 comment added The Photon Something is fishy here. If you just had a transmission line mismatch, you could not have more than 100% overshoot. It would be good to understand the root cause of the problem before trying to suggest an answer. Could you post a photo of the system to make clear the construction of the boards, cables, etc.? A scope trace of the overshoot signal?
Jul 25, 2012 at 15:36 comment added stevenvh Peter, have you tried higher values for the RC than 100 ohm, 1 nF? At 800 kHz it may distort your pulses, and maybe give receive errors, but I would like to know how it affects the overshoot. How about 1 kohm and 10 nF?
Jul 25, 2012 at 14:50 comment added stevenvh @clabacchio - I should think so. 12 V on a 5 V supply is 140 % overshoot.
Jul 25, 2012 at 14:43 answer added Andrejs Cainikovs timeline score: 0
Jul 25, 2012 at 14:34 comment added clabacchio Do you have a specific issue with the spikes?
Jul 25, 2012 at 14:16 history asked Peter CC BY-SA 3.0