Early Prototype

A project log for ESP GPS NTP Server

A simple NTP server using GPS

liebmanliebman 11/15/2017 at 03:300 Comments

  I threw together a quick prototype using a NodeMCU, small oled display and a gps unit. Then spent some time working with the software. 

   I had seen a number random crashes and found that this was due to power demands from the GPS module so I added a large-ish capacitor nearby. 

   Since the ESP8266 only has one USART I’m using a software serial implementation.  I've still seen some crashes and decoding the stack trace they are happening on the interrupt service routine for this module.  A quick look at the modules code shows a WAIT macro that may not be safe in an interrupt service routine,

   I'm also using a nice, small NMEA parsing library to parse the GPS messages.  

   Its responding to ntp requests and syncing with the PPS signal from the GPS unit.  I am seeing a few times where the NMEA message from the GPS is parsed after the next second pulse from the GPS.  Because I'm validating validating that the time I have is correct with each message I see it time warp back one second then timeworn forward one second a few times a day.  I think that the ESP wifi housekeeping functions may sometimes delay the serial parsing.  Or that rendering the display could be taking too long to render each second.