Internal GPS Mod Tech Support/Q&A
- Thread starter jonwienke
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I finally received the ATGM336H today.
BDS GPS Dual-mode Module Flight Control Satellite ATGM336H Replacement NEO-M8N S
I installed it by driving the TTL side of the RS232 UART directly from the GPS module since both are 3.3 v compliant but I'm not seeing any GPS activity recoginzed by the HomePatrol.
Did you drive direct or go through an RS-232 adapter?
The spec sheet says it defaults to 9600 and I tried that plus all other baud rates, still nothing.
Did you use the RX line as well? I only tacked TX output to the TTX output (pin 15) of the UART.
BDS GPS Dual-mode Module Flight Control Satellite ATGM336H Replacement NEO-M8N S
I installed it by driving the TTL side of the RS232 UART directly from the GPS module since both are 3.3 v compliant but I'm not seeing any GPS activity recoginzed by the HomePatrol.
Did you drive direct or go through an RS-232 adapter?
The spec sheet says it defaults to 9600 and I tried that plus all other baud rates, still nothing.
Did you use the RX line as well? I only tacked TX output to the TTX output (pin 15) of the UART.
The scanner default baud rate is 4800, and the GPS is 9600. The scanner and GPS settings have to match, or the scanner will not recognize a GPS is connected.
I used a MAX3232 converter to convert to RS-232 rather than driving TTL direct. I did not connect the GPS RX line to the scanner TX. The only time you need to connect anything to the GPS RX is if you want to change the GPS configuration settings.
If you're bypassing the scanner UART, you have to pull the chip completely, or at least cut the output lead off the chip so it is no longer connected to the output trace. Having multiple TTL outputs tied together can have unexpected results, depending on exactly how the output signalling is done. It's possible that the low voltage is still ~1.5V rather than 0V and is too high to register as a signal state change. It's also possible that you damaged the GPS TTL output by connecting it to an external voltage source. Cut the scanner UART chip out of the circuit, then check your connection with an oscilloscope to verify that the GPS data signal is swinging from 3.3V to 0V. If you have the scanner baud rate set to 9600 and still no data is received, then you either have a bad connection somewhere, or too many cooks spoiling the soup.
I used a MAX3232 converter to convert to RS-232 rather than driving TTL direct. I did not connect the GPS RX line to the scanner TX. The only time you need to connect anything to the GPS RX is if you want to change the GPS configuration settings.
If you're bypassing the scanner UART, you have to pull the chip completely, or at least cut the output lead off the chip so it is no longer connected to the output trace. Having multiple TTL outputs tied together can have unexpected results, depending on exactly how the output signalling is done. It's possible that the low voltage is still ~1.5V rather than 0V and is too high to register as a signal state change. It's also possible that you damaged the GPS TTL output by connecting it to an external voltage source. Cut the scanner UART chip out of the circuit, then check your connection with an oscilloscope to verify that the GPS data signal is swinging from 3.3V to 0V. If you have the scanner baud rate set to 9600 and still no data is received, then you either have a bad connection somewhere, or too many cooks spoiling the soup.
I wondered about it being in line causing the issue. Thanks. I will just drop one of the small 232 boards in.
I'm still having issues with the ATGM336H module. When I power it up a red led glows steady. Do you know if it's supposed to blink when GPS is locked? Watching the output on a meter I see a 1 Hz pulse but it only goes up to about 2.5 volts.
Oh, now it's finally blinking....
Oh, now it's finally blinking....
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The on-board LED is steady on until it gets satellite lock, then it flickers off briefly once per second.
The PPS output stays low until the module gets lock, then it pulses high once per second.
Be patient. First fix from a cold start with a dead backup battery can take 5-10 mins. It goes a lot faster if you can give the module good reception conditions.
The PPS output stays low until the module gets lock, then it pulses high once per second.
Be patient. First fix from a cold start with a dead backup battery can take 5-10 mins. It goes a lot faster if you can give the module good reception conditions.
OK I put it back together (can't see the led now) but still no GPS indication from the radio.
EDIT: Was able to crack it open and keep it running and I see it's blinking so it's locked.
I'm feeding the RS232 TTL board from 3.3v. I wonder if I should give it 5v? Obviously the data is not making into the radio correctly.
EDIT: Was able to crack it open and keep it running and I see it's blinking so it's locked.
I'm feeding the RS232 TTL board from 3.3v. I wonder if I should give it 5v? Obviously the data is not making into the radio correctly.
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Check the current draw of the MAX3232. If it doesn't start properly, it won't output anything on the RS-232 side, and will draw over 100mA. Is it getting hot to the touch? It should run fine on 3.3V, though.
Are you sure you didn't damage the output of the GPS by connecting it in parallel with another output? It's possible you could have damaged the output doing that.
Do you have access to an oscilloscope to see that the TX output on the GPS is doing?
Are you sure you didn't damage the output of the GPS by connecting it in parallel with another output? It's possible you could have damaged the output doing that.
Do you have access to an oscilloscope to see that the TX output on the GPS is doing?
I'm not sure that it's not damaged. I need to check that. I do have a scope but it's cumbersome (HP8935 test set). I have a Saleae logic analyzer though that should be easier to at least see if it's kicking out correct data.
The Saleae Logic analyzer spit out good data. I can see proper LAT / LONGs. Something must be going on with the 232 adaptation.
OK good, you didn't fry the GPS TTL output. Keep in mind that the MAX3232 has 2 separate data paths, one on the top of the board and one on the bottom. An input on the top of the board is connected to the corresponding output on the top of the board, and vice versa. You can't use an input on the top of the board and expect it to connect to an output on the bottom of the board.
I'm using the same side (bottom) since the double sticky 3M tape adhered better to the chip. I had the TX of the module connected to the --> of the TTL side and the --> of the RS232 side going to the RXD pad. The 232 module is grounded to the same point as the GPS module. 232 module power is drawn from the RG_OUT 3.3v point near the audio jacks.
I find this module is not as sensitive as the UBLOX GP735 I used previously. That one never lost lock inside. This one is losing it periodically in the same spot. Hopefully it will be good enough mobile if I can get the thing to talk.
It's spitting out data like this:
1234.5678 N 012345.6789
Obviously mock numbers but that's the format. The actual numbers are correct. It packs in a lot of other data and ends with ANTENNA "OK"
That looks like proper NMEA0183 formatting to me unless I'm incorrect.
I'm starting to question the radio's 232 UART now, or maybe the 232 board too.
I find this module is not as sensitive as the UBLOX GP735 I used previously. That one never lost lock inside. This one is losing it periodically in the same spot. Hopefully it will be good enough mobile if I can get the thing to talk.
It's spitting out data like this:
1234.5678 N 012345.6789
Obviously mock numbers but that's the format. The actual numbers are correct. It packs in a lot of other data and ends with ANTENNA "OK"
That looks like proper NMEA0183 formatting to me unless I'm incorrect.
I'm starting to question the radio's 232 UART now, or maybe the 232 board too.
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02:59:27 $GNGGA,025927.000,3955.0546,N,07735.0672,W,1,10,1.1,201.3,M,0.0,M,,*62
02:59:27 $GNGLL,3955.0546,N,07735.0672,W,025927.000,A,A*56
02:59:27 $GPGSA,A,3,12,25,32,14,15,21,10,18,24,,,,1.9,1.1,1.6*34
02:59:27 $BDGSA,A,3,14,,,,,,,,,,,,1.9,1.1,1.6*29
02:59:27 $GPGSV,3,1,10,10,76,328,37,12,21,103,16,14,32,268,23,15,12,076,25*7A
02:59:27 $GPGSV,3,2,10,18,71,123,30,21,22,189,12,24,43,053,26,25,15,139,27*7B
02:59:27 $GPGSV,3,3,10,31,08,210,,32,48,281,22*77
02:59:27 $BDGSV,1,1,01,14,21,110,15*5B
02:59:27 $GNRMC,025927.000,A,3955.0546,N,07735.0672,W,0.37,204.24,180817,,,A*62
02:59:27 $GNVTG,204.24,T,,M,0.37,N,0.69,K,A*28
02:59:27 $GNZDA,025927.000,18,08,2017,00,00*46
02:59:27 $GPTXT,01,01,01,ANTENNA OK*35
First and second lines are time and location.
Lines 5, 6, and 7 are satellite status info.
Line 9 is time and position data in an alternate format.
The connections sound right. But I've found I had to put a 220uF capacitor across the MAX3232 power leads, and a 220uH inductor on the power lead going to the MAX3232 module. Otherwise it randomly starts in an error state, draws excessive power, outputs no RS-232 data, and eventually fries itself. It also requires all unused RS-232 inputs be tied to Vcc, or the same startup error happens.
I have a pile of MAX3232 modules that no longer contain their magic smoke.
Definitely break out the o-scope to see what the RS-232 side of the module is doing.
02:59:27 $GNGLL,3955.0546,N,07735.0672,W,025927.000,A,A*56
02:59:27 $GPGSA,A,3,12,25,32,14,15,21,10,18,24,,,,1.9,1.1,1.6*34
02:59:27 $BDGSA,A,3,14,,,,,,,,,,,,1.9,1.1,1.6*29
02:59:27 $GPGSV,3,1,10,10,76,328,37,12,21,103,16,14,32,268,23,15,12,076,25*7A
02:59:27 $GPGSV,3,2,10,18,71,123,30,21,22,189,12,24,43,053,26,25,15,139,27*7B
02:59:27 $GPGSV,3,3,10,31,08,210,,32,48,281,22*77
02:59:27 $BDGSV,1,1,01,14,21,110,15*5B
02:59:27 $GNRMC,025927.000,A,3955.0546,N,07735.0672,W,0.37,204.24,180817,,,A*62
02:59:27 $GNVTG,204.24,T,,M,0.37,N,0.69,K,A*28
02:59:27 $GNZDA,025927.000,18,08,2017,00,00*46
02:59:27 $GPTXT,01,01,01,ANTENNA OK*35
First and second lines are time and location.
Lines 5, 6, and 7 are satellite status info.
Line 9 is time and position data in an alternate format.
The connections sound right. But I've found I had to put a 220uF capacitor across the MAX3232 power leads, and a 220uH inductor on the power lead going to the MAX3232 module. Otherwise it randomly starts in an error state, draws excessive power, outputs no RS-232 data, and eventually fries itself. It also requires all unused RS-232 inputs be tied to Vcc, or the same startup error happens.
I have a pile of MAX3232 modules that no longer contain their magic smoke.
Definitely break out the o-scope to see what the RS-232 side of the module is doing.
Well the data format looks good then. I've ran into that issue with the ebay 3232 to 9 pin serial breakout modules before where they get hot and fry. I will need to look into that. I need to find my uniden gps cable and test the radio's ability to work with GPS too I suppose.
I've never had this much difficulty doing this. Usually it all just works but this one wants to fight.
I've never had this much difficulty doing this. Usually it all just works but this one wants to fight.
What are you 232 output voltages looking like normally? I'm seeing a max of -3.2 v coming out of it.
The MAX3232 is a finicky PITA and is most likely your problem. Overheating them can cause the RS-232 output to permanently sit at a random voltage and not track the input. They're the chip equivalent of the crazy girlfriend you kind of like, but really ought to dump before you wake up with a slit throat in the trunk of a stranger's car. Half the reason I went with the Reyax module is to connect the GPS directly to the scanner without dealing with the tantrums and BS of the MAX3232.
Total RS-232 voltage swing should be about 3x the supply voltage when you tie an unused RS-232 input to Vcc. So if you power with 3.3V, a logic 0 should be about -5V, and a logic 1 should be about +5V. If Vcc is 5V, then you should see approximately ±7.5V. If the highest RS-232 output voltage is -3.2V, then the chip is fried; trash it and get a new one.
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