Recording two serial output signal simulteneously - Page 1
Forum section: electronics / testgear

author: tkamiya
author_rank: Super Contributor
timestamp: March 28, 2019, 12:14:02 am
content: I am doing an experiment involving two devices.Device A is a GPS which only outputs serial data and 1 ppsDevice B is a Rubidium Oscillator which accepts 1 pps, and spits out (corrected) pps and 10MHz.Independently, they both seem to work fine. No anomalous behaviors as reported by Lady Heather.However, when I connect 1 pps from A to 1 pps INPUT in B, odd things happen. At this time, I am monitoring device B using LH. All the sudden, temperature rises to few THOUSAND degrees, loses Physics lock, and few other parameters go NUTS. It only lasts very short period.I am assuming something is happening with Device A's pps and that is causing Device B to act out.Are there any device that can record two channels of serial data for 24 hours or more? There ought to be, but I have never seen it. Experiment is still at very early stage. I don't have very much data. So that's all I can offer.Anyone?

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: March 28, 2019, 12:47:13 am
content: What's the baud rate and amoubt of data on those channels? Computer with Serialtest or related SW, which is able to timestamp data aquired on two serial interfaces into one consolidated view (up to 115kB afaik) might be able to do that.You have to calculate your storage needs, of course.

author: 0culus
author_rank: Super Contributor
timestamp: March 28, 2019, 01:26:58 am
content: Logic analyzer with glitch trigger?

author: DaJMasta
author_rank: Super Contributor
timestamp: March 28, 2019, 01:42:42 am
content: Don't know what scopes would support it, but if there's a way to dump the decoded serial data from a scope's channel decode into a file or over USB, it would be pretty low bandwidth so it probably wouldn't be hard to do a long term recording.This could also be an option for a simple Arduino, PIC, STM32, or similar development board and a simple sketch. Wouldn't be hard to make it talk to two serial ports and just return each to the computer as a single serial stream, then log it on the PC. You've likely got the parts lying around to do it for free, too!

author: texaspyro
author_rank: Super Contributor
timestamp: March 28, 2019, 04:13:23 am
content: Heather can write serial port data capture files. They have all the data sent by the device (but not the commands sent to it). See the WY keyboard command.

author: Tom45
author_rank: Frequent Contributor
timestamp: March 28, 2019, 04:24:41 am
content: Run two copies of Realterm, each set up to capture from a serial port to a file. Turn on the time stamp that prefixes a time stamp to the start of each line of serial data.

author: tkamiya
author_rank: Super Contributor
timestamp: March 28, 2019, 06:23:32 am
content: Quote from: texaspyro on March 28, 2019, 04:13:23 amTHIS and log file will do it. For some reason, PRS-10 alone works fine. Resolution-T alone works fine. But when combined, PRS-10 goes into nuclear fusion!

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: March 28, 2019, 04:02:14 pm
content: Are you sure that this is not a power supply related problem? Like grounded vs. floating or something akin to that?

author: tkamiya
author_rank: Super Contributor
timestamp: March 28, 2019, 04:13:33 pm
content: ANYTHING is possible.I just switched the GPS part to a totally different unit. Problem replicated. Since PPS input affecting temperature or any other parameter is NOT reasonable, I am also thinking something along that way. Since I have a few PRS-10, I can also try different one.

author: extide
author_rank: Regular Contributor
timestamp: March 28, 2019, 04:17:02 pm
content: Check out this thread:https://www.eevblog.com/forum/metrology/what-do-you-want-from-a-gpsdo/Not sure what GPS module you are using but they can be susceptible to lots of jitter on those 1pps outputs -- perhaps that is causing an issue?

author: tkamiya
author_rank: Super Contributor
timestamp: March 28, 2019, 04:20:41 pm
content: PRS-10 has a kind of filter that if PPS does not arrive in certain time frame from previous one, it will discard it. Then wait for 256 good ones to arrive. Then it restarts PLL. So that's not likely. I'll replace PRS-10 and see.

author: tkamiya
author_rank: Super Contributor
timestamp: March 28, 2019, 06:41:25 pm
content: I feel very silly now....I've replaced the PRS-10 itself with a spare unit and it is working fine. I'm going to run it for 24 hours and see if problems reproduce. So far, so good....