Author Topic: Symmetricom S200 with GPS interposer fixes Furuno GT-8031 week rollover issue  (Read 1304 times)

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Offline tverbeureTopic starter

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My flea market Symmetricom S200 came with a Furuno GT-8031 GPS module that suffered from the 1024 week rollover. Because of it from some reason, the S200 refuses to lock to the GPS 1PPS signal, even though there's really no reason why it shouldn't. (The date will be wrong, but who cares?)

The solution is to send a "@@Gb" command to the GT-8031 module that gives a hint about the current date.

There are at least two ways of doing that: Alex Forencich was able to patch the HCS12 microcontroller on his S350 to send this command at boot up. He posted about his solution yesterday:

I went the other way and created an interposer PCB with an RP2024-zero that can intercept UART messages to and from the module and modify those messages or insert new ones. I finally got that to work today.

The interposer uses an RP2024-zero to intercept, insert, and retransmit messages from and to the GPS module. It has a few connector and resistors, and when not powered by a USB cable, it's powered by a +5V pin on the S200 motherboard.

The Furuno GT-8031 plugs in on top of it. I still need to buy the right spacers to make it solid...

« Last Edit: June 01, 2024, 06:57:51 am by tverbeure »
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Offline testpoint1

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the receiving sensitivity of GT-8031 is quite poor, you may consider change it to GT-8736:

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