There are tools on github like gps-sdr-sim and others that allow to generate simulated range data is then used to create the digitized I/Q samples for the GPS signal for hackrf, limesdr, bladerf etc. The simulation start time can be specified if the corresponding set of ephemerides is available. Ephemeris for current day, week is available on Nasa website.
Is it possible to generate ephemeris data for static transmitter (fake satellite) which is on the ground? Will gps receiver fix its coordinates?
Related
I am looking to use either NEO-6M module or Grove-Air530 for a GPS project (with Raspberry Pi). But in addition to latitude and longitude coordinates, I need to receive satellite info such as its identity, current position in the sky, etc. Does either of these module record such data (or rather, do GPS satellites embed such data when transmitting coordinates to these modules)?
Good evening!
I'm configuring NTP on an embedded Linux system connected with an U-Blox GPS receiver. I've used NTPD and GPSD.
I would like to know what's the technical difference between:
PPS Signal provided by the GPSD shared memory SHM, (Pseudo IP Address 127.127.28.1);
PPS Signal "Stand Alone", but always connected in some way I would like to understand, with GPS (Pseudo IP Address 127.127.22.0)
It is critical for me to understand because I really need an high level synchronization and I would like the right information from the receiver.
Searching all over the web I've found only confused answers to my doubt...
Thanks in advance!
FL
The SHM driver is not designed to provide a PPS signal by itself. So maybe your notion here is misguided.
A PPS signal is used for getting a (precise) notion of the
frequency of the local clock (the one used for measuring external signals), as it just provides a well known timing distance of the "pulses" (1s in this case). Actually pps is a frequency source.
GPSD on the other hand is communicating with some device (could be built into your HW). It then proovides the time data read from the GPS source via shared memory to ntp. This provisioning of data does not guarantee any timing relation (delay). (E.g. could occur earlier or later within the second due to load or scheduling)
From the perspective of ntp, you will have a true date/time label, but you might not know exactly when the related point in time did occur related to your local clock. (Usually not precisely enough for common ntp use cases.) This is where PPS kicks in.
Depending on how the GPS device is being connected to your local machine (parallel, serial, internal bus) you will have some way of getting an interrupt on the pulse from the pps signal. (e.g. with serial connection you usually will get a transition on the DCD pin).
The internal processing of the related interrupt will read the local clock and the resulting timing information is then provided for further processing. This information is exactly what the PPS clock discipline is using and providing to ntp. What you need to configure here, is the offset from the triggering of the pulse to reading the local clock. (Pulse usually is assumed to occur "on the second.)
So, in your configuration, it is likely that the "source" of the PPS signal is the same GPSD is using for providing date/time data (your GPS device).
However, the actual signal used for date/time data and pps is different. Date/time will use a data telegram or some register content read from the GPS device while pps will be a level change on an input pin proveded from this very device.
For details start with the interfacing information from your GPS receiver, especialy any timings stated there. Then look at ntp and figure what driver(s) will allow exploiting such input data for best time quality.
I have a GPS circuit board from china. The only information I can find on this thing is :"amoj GPS 04C www.amoj.com"
It has a serial (DB9) connection and I would like to determine how to putty into it or something.
How can I determine what the port settings that are required to access this?
Pictures below:
Photos in Dropbox
The Jupiter TU60 serial interface is 9600 8N1 by default. The only sentence it will output automatically is the flash checksum message about a second after power up. Google the datasheet for the device and it will let you know about this.
To have it output the position and other information, you must command it to do so. There is a default set of commands that are active after power up. They begin with ## and are from the protocol used by Motorola. Refer to the M12+ Users Guide and Supplement (available online) for information on how to use these commands. I have been able to enter them from Realterm. The only tricky part is calculating the checksum. You can use most hex calculators to do that.
According to the datasheet, the unit goes into survey mode automatically and after about 24 hours goes into position hold. The 1PPS and 10KHz signals are valid to less than a microsecond after a few minutes after power up and to 50nS after a day. I have compared this to another standard I have to verify this. You can use the ##Ea command to get the status of the unit and the M12+ Manual will tell you how to decode it.
Look for $GP... messages at 4800 and 9600BPS as yegorich suggest. Common NMEA messages output by GPS devices are $GPGGA, $GPVTG, $GPRMC.. If you find that data coming out, use Google to look up NMEA 0183 sentence structure and you will have what you need...
I have the same board with the Navman jupiter T Tu60 GPS 1pps 10khz GPS Module on it. I just received my sma antenna and have hooked it up. I am using 12.6V power to the centre pin.
It outputs 1pps on the led with no signal, so that is not to be trusted. Mine is labeled 1pps and 10khz underneath the pcb but these are actually swapped! I put the 10KHz output on my dso and get a 10KHz square wave 50% duty cycle signal but there is ringing on the waveform rise so I have to set the trigger level to 0.8v to get the dso to register the 10KHz frequency. I suspect this may be because the output expects a load and is not seeing one. Now, was I using ac or dc coupling?
I too am getting nothing on the serial. I tried 9600, 4800 using putty on com1 (I have a nice old motherboard) and then tried reversing rx and tx but no luck. As of now I am checking out the serial signals with the dso to see if I can work out what is happenning. I suspect that these boards are rubbish, and useful as power supplies only.
It reads 10.0000 on my hp 5328a counter and sometimes reads 9.9999. It would be nice to be able to talk to the gps to see whether it has satellite lock.
Please let me know how you get on and if you find out any further info.
Brett VK6EZ.
Is there anybody has ever used Trimble GPS (global positioning system) receiver, and wrote any GPS driver to output GPS data onto ROS (robot operating system) topics?
If your Trimble outputs NMEA sentences, you should be able to use the nmea_navsat_driver to read them. If you can read them via serial port, you can try the nmea_serial_driver to publish directly from the port. If it outputs via some other protocol (e.g. TCP or UDP), you'll need to write your own driver to get the NMEA sentences onto ROS topics - at that point you can use the nmea_topic_driver to process the raw sentences.
I am working on a project which uses a PIC24FJ64GA002 mcu.
I am working on a bit-banged serial communication function that will use one wire to send data and then switch to receive mode to receive data on the same pin. A separate pin will be used for clocking which will always be controlled by a different board (always an input). I am wondering is there a way to configure the pin for open-collector operation that that it can be used as an input and and output or do I have to change the pin configuration every time i go from reading to writing?
You need to change the direction of the pin each time by using the TRIS register. If the pin is set up as an output, reading the PORT register will most likely only tell you what level you are driving the pin to (assuming there is a high impedance on the pin). If the pin is set for input, you won't be able to drive your desired output value.
Also, make sure that you read incoming data using the PORT register, but output the data using the LAT register. This ensures that you don't suffer any issues if your code (I assume you are programming in C here) gets converted into bset/bclr/btgl instructions which are Read-Modify-Write. If you are writing in assembler, the same rule applies but you know when you are using these R-M-W type instructions. If you want more reasoning on this, please ask.