[time-nuts] cheap GPS receiver (NavSpark) with timestamp feature

beale beale at bealecorner.com
Fri May 30 20:23:26 EDT 2014


It seems there is some interest in an inexpensive GPS receiver with a timestamp feature. 

As far as I know, the recently released NavSpark ( http://navspark.mybigcommerce.com/ )
may be the least expensive such device available. It was a crowd-funded effort from an established small GNSS design 
house in Taiwan (Skytraq).  Recently I received some of the first of these items. It is programmable using a modified 
"Arduino" type development environment, and uses a 32-bit CPU (LEON3 Sparc-V8) for baseband processing with a 
3rd party L1 receiver section (Skyworks SE4150L).

The 1PPS output signal has a granularity of 10 ns, but the input signal timestamp feature is ~60 ns (GPS model with 
16.368MHz clock) or ~40 ns (GPS + GLONASS model with 24.552MHz clock).  I only just tested the demo timestamp 
code on a GPS model this morning, and it works mostly as expected, generating timestamps (text output on one of 
two UARTS) based on 1PPS input from a not-calibrated OCXO I had lying around. At least the millisecond output has 
jumps of ~ 60 ns size. The GPS time-of-day conversion seems to have a roundoff problem at the microsecond level.  
The NavSpark contains a TCXO of unknown performance, but with the entire unit costing $22 at retail, it's not gold-
plated.

484282681.511417 ms, week #1794 since 1980;  2014-05-30 @ 02:31:06(+0.68151140) PM
484283681.511432 ms, week #1794 since 1980;  2014-05-30 @ 02:31:07(+0.68151140) PM
484284681.511452 ms, week #1794 since 1980;  2014-05-30 @ 02:31:08(+0.68151093) PM
484285681.511488 ms, week #1794 since 1980;  2014-05-30 @ 02:31:09(+0.68151093) PM
484286681.511498 ms, week #1794 since 1980;  2014-05-30 @ 02:31:10(+0.68151093) PM
484287681.511514 ms, week #1794 since 1980;  2014-05-30 @ 02:31:11(+0.68151093) PM
484288681.511524 ms, week #1794 since 1980;  2014-05-30 @ 02:31:12(+0.68151188) PM
484289681.511536 ms, week #1794 since 1980;  2014-05-30 @ 02:31:13(+0.68151188) PM
484290681.511541 ms, week #1794 since 1980;  2014-05-30 @ 02:31:14(+0.68151188) PM
484291681.511554 ms, week #1794 since 1980;  2014-05-30 @ 02:31:15(+0.68151188) PM
484292681.511570 ms, week #1794 since 1980;  2014-05-30 @ 02:31:16(+0.68151093) PM
484293681.511578 ms, week #1794 since 1980;  2014-05-30 @ 02:31:17(+0.68151093) PM
484294681.511538 ms, week #1794 since 1980;  2014-05-30 @ 02:31:18(+0.68151093) PM
484295681.511564 ms, week #1794 since 1980;  2014-05-30 @ 02:31:19(+0.68151093) PM
484296681.511588 ms, week #1794 since 1980;  2014-05-30 @ 02:31:20(+0.68151093) PM

---
John Beale
www.bealecorner.com



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