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Tips and questions relating to the GPS modules from SFE
By BigRedBee
This is weird.

I've got an EM406 happliy working on a circuit board talking directly to a PIC 16LF88. Not a problem at all on at least 10 different EM406 modules. Today, I assembled a few more using a NEW batch of EM406A's that I just got direct from USglobalsat. NONE of them work -- all just send garbled data.

I take a board and an EM406 that works, swap out the EM406 for a new one, and it fails. Just garbled data. It does blink, indicating that it's locked, and that (garbled) data coming out seems to be about once per second. I then take the good unit, and connect via a MAX232 to hyperterm. Good data -- now swap in the new one -- garbled.

Ideas? Comments? Suggestions?

GPS is running off of 5V bench supply. NMEA is expected at 4800 baud. EM406 Input pin is tied high. SirfDemo can't synchronize protocal/baud rate.


-- Greg
By BigRedBee
THIs is getting stranger and stranger.

On the working board, the TX line from the EM406 is normally high (3 volts) and then goes low when it transmits. I can clearly measure the 1 second period between transmissions.

Same board -- just swap in a different EM406, and now, the TX line is normally LOW (actually, about -600mv) and goes high (5 volts) during transmit. TIme between transmissions is also about 1 second.

Rise time on the broken modules is also dramatically longer -- about 120ns vs 10 ns on the working board.

Did I get a bad batch of parts?

-- Greg
By BigRedBee
I believe this problem is resolved. I took a careful look at my invoice, and the part number is listed as ER-406A not EM-406A

Any guess what the 'R' stands for? That's right -- RS232. I searched the USGlobalSat website, and don't see any reference to that part at all -- but the ER-series are listed as RS232, while the EM series is TTL level.

Phew -- glad that's taken care of. Now -- let's hope it's an easy process to get replacement parts!!!

-- Greg
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