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Tips and questions relating to the GPS modules from SFE
By BigRedBee
#45615
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.

Grrrrrrr.......

-- Greg
By BigRedBee
#45617
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
#45619
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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