stratum-1 gps/pps timeserver project (rasp pi) - Page 1
Forum section: electronics / projects

author: linux-works
author_rank: Super Contributor
timestamp: December 25, 2014, 08:09:00 pm
content: most tech info came from this link:http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.htmlalso here:http://ntpi.openchaos.org/pps_pi/now, on to the pics!now, the details:this box is a lot of thingsstart out with a raspberry pi (new model), then soup it up until there are lots of flashing and non-flashing leds on add-on boards.the lcd is a regular hitachi 4x20 lcd with a pcf chip port expander, same as what we use on the lcduino d1 and d2 boards. this seems to be some kind of common pin-out that the rasp pi guys use, so I also used it. its mounted on a perfboard backpacked to the lcd module. also on there is a PE chip to scan the 5 key arrow keys, up front (and drive 3 user-settable color leds). the front also has an i2c (everything on the front is i2c, on purpose) RTC module for time backup.for power supply, I have a dc/dc converter that will take the laptop standard range of 12v-20v and still give me a clean reliable 5v out. the pi really needs a good solid 5v sent right to it. for fun, I found a car computer store selling UPS modules that use TI chips for very fast failover. they also charge standard 12v SLA batteries, so I wired that module in and there are 2 dc jacks in the back; one is clearly marked for the battery and one is for the wall-wart laptop dc supply. its pretty cool and was under $50 for that module on amazon/ebay.I have a $15 ublox gps module with a wire hack for the led PPS output. the linux kernel is modified to notice one of its GPIO pins as a pulse-per-second line and this keeps the time very accurate. the gps values give the seconds -values- but the pps signal gives it the exacting starting boundary. this is the key to being an 'atom' clock in terms of NTPd terminology. I connect the serial ttl output of the gps module to the serial in of the pi and start gpsd at boot time. ntpd is also modified to have a shared mem segment with gpsd and together they report stratum-1 as the ntp server level. for this rasp pi! too damned funnyone neat trick was finding this extension module for the micro sd card slot. amazon has a vendor that makes these and I was able to find a micro-sd to standard sd with a very short flex-pcb cable. really neat device! lets me 'remote' the sd card slot. you can see the micro-card inside a standard sd card as a holder. the company is working on a micro-to-micro version (they have asked me for some mounting hints for their board, so maybe I'll see some samples of that new design, soon). also on the side is the native htmi port. in case you need it - but normally, I expect this box to be a server and be headless, other than the lcd display and front panel buttons and leds.for IoT playing (I'm sort of getting into that, at work) I added an 8-port a/d module (10 bit) so that I can read regular old analog sensors (light level, temperature, voltage, pot position, xyz accelerometers, etc). finally, there is an IR sensor in the back in case you want to turn this into an mpd music player and control it via a sony handheld remote(yes, it works great with a usb/spdif dongle, mounting music files via the network and showing the song name/etc on the lcd display while using LIRC to remote control it all).

author: linux-works
author_rank: Super Contributor
timestamp: January 06, 2015, 03:46:06 pm
content: btw, if anyone wants a copy of my sd-card image, PM me and I'll upload it to my ftp server. I could also copy the card to your card if you want to mail me a blank card to write to. I use 16gb sd cards (since they are cheap) but the image will fit on an 8gig or even a 4gig card. 8gig or more is suggested, though, so you have room to build source code and do updates.I also can make more of those boxes on my lasercutter, so if you have any interest in those, I could do a short infomal run and make a few extras.