Anybody have any info on the Skytraq 524c (Venus 5?) chip?

GPS/GNSS Development Boards
1

I recently acquired a (very) cheap USB GPS dongle that when opened, reveals a skytraq venus 524c chip inside, which I am guessing is a Venus 5 family chip.

I am wondering if anybody has a schematic for this chip, as it seems as if the dongle (with its integrated active patch antenna) would make a great gps core for a homebrew NTP (time) server, perhaps integrated into my WLAN router, if I can get access to its 1PPS signal.

I know that 1PPS is available on the 521 chip.

Ive been unable to find anything on the 524c except a mention in a old press release:

"The newly introduced Venus 120 with currently in-production Venus 5 single-chip baseband products (Venus 521/522/524) constitute a high-performance 44-channel -158dBm-tracking GPS/AGPS chipset. Footprint of a complete GPS receiver module can be as small as 12mm x 14mm . The tracking current is 45mA running full power. "

To keep accurate time, I need to extract the 1PPS signal.

There is no name on the dongle itself (just the word GPS in red) but it was sold as a unitraq UD-731 The board is very small and is marked “UD-731R Rev 0.3” written on it.

The main chip:

skytraq

venus 524c

P4880-010

Here’s what the “skytraq-datalogger” tool returns to me:

./skytraq-datalogger --info

kernel version: 1.1.16 – ODM version: 1.3.21 – revision: 2007-04-14

log_wr_ptr: 16777215

total sectors: 32994

sectors left: 0

max time: 1614807040 s

min time: 7340032 s

max distance: 16257024 m

min distance: 0 m

max speed: 4194315 km/h

min speed: 1835130 km/h

datalog enable: 28

log fifo mode: 0

AGPS enabled: 0

AGPS data left: none

baud-rate: 4800 bps

If anybody has specific data on how to access the 1PPS on this skytraq 524c chip- its schematic or any other relevant data I would be very grateful for a copy of it. Please reply here or via email.

My email is (reverse the following) liamg{at}4202muillirt

Thank you

2

More on the 524c based dongle. I’ve been able to get substantially more accuracy in timekeeping by configuring the NMEA output to only output the GPRMC sentence using the GPS Viewer app.

But it appears that commands that it recognizes are unpredictable and the unit will often sometimes become unresponsive after receiving a command.

I’m curious if the changes will stick because this sounds quite similar to the pin 9 problem reported here on the Venus 6 chip.

The chip on the board is a 52 pin SMD chip, square. 13 leads per side.

The entire GPS is roughly 2.5 x 5 cm, including the USB plug.

Does anybody think that I might I hurt anything by exploring the pins with a shield grounded, high impedence, logic probe to find which one is the PPS?

3

The 1PPS signal is on pin 45 of the 52 pin package. (and thank you to Oliver at Skytraq for giving me that info.)