Thanks, I'll look at them. On 19 April 2014 19:12, Ray Richter wrote: > I've used the LANTRONIX UDS-10 in the same way you want to. So far I've b= een > lucky by using 'Feedthru' capacitors, mostly from AVX or TDK. In your cas= e I > think I would try going from 'Signal' to chassis ground first instead of = the > negative rail. Feedthru caps come in different sizes and you might have t= o > play around a bit to find the correct size. At 9600 baud you should be ab= le > to use the larger sizes. They do make dedicated filters for serial > communications but, the Feedthru caps should be the cheapest and most > reliable route. > > Ray > > Ray Richter > UniMatrix Technologies > rrichter@unimatrixtech.com > >> -----Original Message----- >> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On >> Behalf Of KPL >> Sent: Monday, April 07, 2014 3:45 PM >> To: PICLIST >> Subject: [EE] noise-proofing open serial interface lines >> >> Hi, >> >> I'm building a simple controller for an irrigation setup. Serial >> interface is being used for configuration, there is no local keyboard, >> and most probably there will be no local screen, as config changes are >> going to be very rare. >> I have obtained several old serial-ethernet adapters, LANTRONIX UDS-10, >> so I can reconfigure this controller via ethernet, if such need occurs >> at some point, at all the other instances that will be just a laptop >> computer with TTL-level usb-serial adapter. I have connected wires >> directly to TTL signals of UDS-10 too, just before the output stage. >> I need 9600 bps serial speed, no more. >> >> The problem is, I have seen serious glitches in operation, because of >> noise induced on serial RX line, when there is no adapter connected, as >> it will be most of the time. I have tried both pull-ups and pull-downs >> on RX line, both of which kind-of-worked, but there were differences in >> operation, as it is never known what kind of serial adapter will be >> connected there, and what kind of output stage it will have. >> It looked like pull-down was interpreted as input signal coming, so >> controller switched to config mode. >> I have seen small ceramics capacitors on signal lines, used same way as >> decoupling caps on power line, but what kind of caps should I use >> there, so that they do not unnecessary load the signal? >> >> What would be a recommendation? Pull-up? Pull-down? Cap? Both? >> >> Software for PIC is being written in JAL. It's reading a DS1307 RTC in >> a loop, and switching output lines according to a configured schedule; >> If new data is found in serial buffer, controller switches to config >> mode, and waits for more characters. When ENTER is received, command is >> analyzed and config updated, then config mode switched off. >> >> >> -- >> KPL >> -- >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist --=20 KPL --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .