PMB-648 Advanced Questions
TodK
Posts: 4
I have a PMB-648 GPS unit which works great for me but I have some more advanced use questions is anyone can contribute.
1) I have seen documentation saying that the units can be put into "smart mode" where it answers queries to different elements in plain text answers. This is done by "pulling the RAW contact point down" but this example is shown on a slightly different chip package not the one sold with the plates and the wire attachment. Does the PBM-648 as sold by Parallax support "smart mode" and how do I trigger it? I see there are two exposed pads on the package marked "Boot" and "TP1" or "TPI" are either of these usable for that?
2) I'm using the Arduino and while the chip works great for receiving GPS signals I was hoping someone had advice on sending to the chip over Tx/Rx. I've tried some simple non-destructive Sirf commands using the Sirf format $PSRF103,05,00,01,01*20 from the console window but I don't see any acknowledgement from the unit - which might be normal but it's hard to tell if I'm actually communicating with it correctly.
3) Are there any vendor specific elements/commands to the this chipset that are addressable using $Pxxx where xxx is the vendor code and are these documented anywhere?
What I'm interested in doing is slowing the reporting from the unit for power management purposes. My applications are mostly long-distance hiking so I don't need reports every second and power management is more important than constant reporting. I'd like to be able to set it to report every minutes (or in increments of minutes) and sleep both the Arduino and GPS unit in between reports to save power. Ultimately I hope to incorporate an SD card for logging and LiPo with solar cell for indefinite logging but I need to be able to control my power consumption first.
If anyone has dug into this in depth I'd appreciate any input,
=Tod
1) I have seen documentation saying that the units can be put into "smart mode" where it answers queries to different elements in plain text answers. This is done by "pulling the RAW contact point down" but this example is shown on a slightly different chip package not the one sold with the plates and the wire attachment. Does the PBM-648 as sold by Parallax support "smart mode" and how do I trigger it? I see there are two exposed pads on the package marked "Boot" and "TP1" or "TPI" are either of these usable for that?
2) I'm using the Arduino and while the chip works great for receiving GPS signals I was hoping someone had advice on sending to the chip over Tx/Rx. I've tried some simple non-destructive Sirf commands using the Sirf format $PSRF103,05,00,01,01*20 from the console window but I don't see any acknowledgement from the unit - which might be normal but it's hard to tell if I'm actually communicating with it correctly.
3) Are there any vendor specific elements/commands to the this chipset that are addressable using $Pxxx where xxx is the vendor code and are these documented anywhere?
What I'm interested in doing is slowing the reporting from the unit for power management purposes. My applications are mostly long-distance hiking so I don't need reports every second and power management is more important than constant reporting. I'd like to be able to set it to report every minutes (or in increments of minutes) and sleep both the Arduino and GPS unit in between reports to save power. Ultimately I hope to incorporate an SD card for logging and LiPo with solar cell for indefinite logging but I need to be able to control my power consumption first.
If anyone has dug into this in depth I'd appreciate any input,
=Tod
Comments
Hi Tod,
Welcome to the forums!
The PMB-648 GPS does not do RAW mode AFAIK. It's in Smart Mode all the time. Smart Mode just waits until you poll it. I would just do a timing loop to pull data down a a specific time.
I don't do Arduino, so I can't offer any code.
Jim
I used this feature in some Spin code I wrote awhile back:
CON _clkmode = xtal1 + pll16x _xinfreq = 5_000_000 'SD Card pins: DO_PIN = 22 CLK_PIN = 23 DI_PIN = 24 nCS_PIN = 25 'Serial I/O pins: GPS_IN = 16 GPS_OUT = 17 PC_IN = 31 PC_OUT = 30 'Write indicator: LED_PIN = 26 'Unit ID: UNIT = "0" 'ASCII constants: CR = 13 LF = 10 OBJ sio : "FullDuplexSerial" gps : "FullDuplexSerial" sd : "fsrw" PUB start | ch, i gps.start(GPS_IN, GPS_OUT, 0, 4800) sio.start(PC_IN, PC_OUT, 0, 9600) sd.mount_explicit(DO_PIN, CLK_PIN, DI_PIN, nCS_PIN) filename[7] := UNIT dira[26]~~ waitcnt(cnt + clkfreq) gps.str(string("$PSRF100,0,4800,8,1,0*0F", CR, LF)) 'Switch to SiRF binary protocol at 4800,8,N,1 'Diable Static Navigation waitcnt(clkfreq + cnt) repeat i from 0 to 9 gps.tx(DisStatNav[i]) 'Switch back To NMEA Protocol Message ID 129, leave only GGA and RMC strings and keep speed at 4800 waitcnt(clkfreq / 2 + cnt) repeat i from 0 to 31 gps.tx(BackToNMEA[i]) repeat waitstr(string("$GPRMC,")) getstr(@time, 10) 'if (time[5] == "0" or time[5] == "5") gps.rx if (gps.rx == "A") gps.rx getstr(@lat, 9) waitstr(string("N,")) 'Change to "S" for southern hemisphere. getstr(@lon, 10) sio.str(@time) outa[26]~~ 'Turn LED on during write, so it won't be interrupted by flipping off the power. sd.popen(@filename, "a") 'Open the file to append data. sd.pwrite(@time, strsize(@time)) 'Write the time and position line to the file. sd.pclose 'Do a close to stat the file. outa[26]~ 'Turn off the LED. else sio.tx("*") PUB waitstr(strptr) | ptr, match ptr := strptr repeat while match := byte[ptr++] if (gps.rx <> match) ptr := strptr PUB getstr(strptr, len) repeat len byte[strptr++] := gps.rx DAT filename byte "gpsdata_.txt" time byte "dddddd.ddd," lat byte "ddmm.mmmm," lon byte "dddmm.mmmm",13,0 'SiRF Disable Static Navigation, Message ID 143 DisStatNav byte $A0,$A2,$00,$02,$8F,$00,$00,$8F,$B0,$B3 'Switch back To NMEA Protocol Message ID 129 at 4800 bauds, leave on GGA and RMC strings updating oce per second. BackToNMEA byte $A0,$A2,$00,$18,$81,$02,$01,$01,$00,$01 byte $00,$01,$00,$01,$01,$01,$00,$01,$00,$01 byte $00,$01,$00,$01,$00,$01,$12,$C0,$01,$61 byte $B0, $B3Maybe this will help you get started.
-Phil
Does the chip have any onboard power or report management controls that you know of? I think I may need to settle for sleeping the Arduino unit only and living with the 65mA draw of the GPS chip.
My (very) rough estimation 3 AAAs should support about 17 hours of 65mA and 3 AAs should 32 hours of 65mA draw. Is that correct?
Thanks again,
-Tod
-Phil
I searched the web in the past for low power mode with Sirf units, and when you access in sirf binary mode you should be able to go to low power.
I guess this should apply also to your unit.
I have not tested it yet (my GPS unit is around at the moment..), but from the web search it is not a sleep mode, but a kind of intermittent mode, where the clock and the fixing is still available, at a lower rate. In fact at startup you will have full consumption till clock and almanac sync (and fixing, but I'm not sure), then the unit will drift to a lower consumption.
Let us know your findings.
Massimo
The parallax document linked to in the store has minimal documentation, and although the code samples help, they don't touch at all on configuration, rtc usage, or the battery backed configuration options. I have other questions on this unit I was just logging in to ask, and saw this thread, so I'll create a new thread for those, but I'm very interested in finding out more about this little unit, and what it can be made to do. I've hunted around, and found documentation on the nmea0183 protocol it uses (though it doesn't seem to follow the standard completely) but I didn't find anything at all about it's configuration options. Glad you located them, I'll be taking a look at that document, and see what it tells me about this topic.
So I found a tutorial with someone using the PMB-648 for a specific project so I felt safe lifting his command strings and trying them out. Specifically:
Serial.write("$PSRF103,2,0,0,1*02\r\n"); // Disables GPGSA sentence
This line suppressed the output of the $GPGSA line as advertised. I've seen some of the official NMEA documentation but it doesn't cover the commands below 150 or so, but I found this reference that does: http://gpsd.berlios.de/vendor-docs/sirf/SiRF2-Leadtek.pdf
So I determined that the command to reverse the above command meant changing a byte: $PSRF103,2,00,01,01*02\r\n but the chip kicked back an error about the checksum being wrong.So I needed to find the correct Here is an on-line script that will generate checksums for NMEA strings... brilliant!
http://www.hhhh.org/wiml/proj/nmeaxor.html
Serial.write("$PSRF103,2,00,01,01*17\r\n");// Enables GPGSA sentence
I haven't gotten into power management yet but frequency of reporting is next.
Project link: http://www.designspark.com/files/ds/CK78764_Complete_Documentation_0.pdf (actually a cool project, props!)
Just reporting back to perhaps help others in the future.
Thanks everyone,
=Tod
PS All code is Arduino based.
Using the documentation on $PSRF103 command I was able to suppress any signals I don't want by change the timing of reporting to 0 and change the timing for strings I do want from 1 - 255 seconds. I don't know if changing the timing of the chip to every 60 seconds would actually reduce the power draw in any significant way but makes programming the use cases I'm interested in easier.
After getting that working I wanted to see about sleeping the Arduino unit to save power and I realized that it would be easier to have the unit respond to polling than trying to time waking the Arduino unit to coincide with the GPS unit timing. I was able to get this working by suppressing all the messages and then using the $PSRF103 command to poll the specific data strings I as interested in.
Serial.write("$PSRF103,2,1,1,1*26\r\n");// Polls GPGSA sentence
The final set-up is starting everything, suppressing all the strings, sleeping the Arduino unit until wakes, polls the GPS, logs the data and then sleeps again.
Another data point is that the PMB-604 package contains a rechargeable battery. As it turns out I didn't have the unit plugged in for 4 or 5 days and all the commands I sent to suppress the messages had worn off and it was back to default settings. It might hold a charge longer if the unit is plugged in longer but it seems like it will always revert if it is removed from power long enough. You would probably want to program for that possibility in long term situations.
I haven't played with actual power management since I can't find any examples and I'm kind of afraid of bricking my GPS unit, but it seems like the internal settings will return to normal eventually. There is pad labeled 'boot' on the edge of the package - I don't know if this could possibly be used to reset the factory settings or not.
This probably my last update unless I actually play with the power settings and get any kind of dependable result. I fell like I've done about as much as I can with the 103 commands and I know what's possible and I'm not sure I want experiment with the complex looking power management commands without any clear guidance.
Thanks to everyone who contributed,
=Tod
I want to disable static navigation(ID 143). After I do this, do I have to Switch To NMEA Protocol (ID 129)?
Once I do this, will these settings be saved on a power down? Or do I need to re-configure with every power up?
TIA
--Neal
I'm not sure, but I think it depends upon how long you're powered down. That being the case, I would recommend reconfiguring on every power-up.
-Phil
Gosh, I sure wish I'd said that.
Oh, wait, I did.