I am working on a project that provides GPS data over a USB connection. (among other things of course)
I am using the Maestro A2235-H GPS Transceiver. It connects over UART to a Leonardo/Micro-style Atmega32u4. That is wired to a USB port, which goes to my laptop.
When I first set everything up, I had it all working, I got NMEA Data over serial and parsed it, sent over USB to python, It worked great. But now I cannot get any data from the GPS. I can reprogram the Arduino, and my other sensors work, but I get no Serial Data from the GPS.
All the eagle files are here: GitHub - Timvrakas/NASA-PCBs: Some work for SSI, NASA, and USGS
The GPS datasheet is here
It has one passage that I had not seen earlier, I think could be the culprit...
10.2 Proper Shutdown and Power-On-Reset (POR)
The A2235-H modules require an orderly shutdown process to properly stop internal
operation and complete any writes of critical data to BBRAM or EEPROM data area.
Abrupt removal or drop of main power while the system is running has risks ranging
from minor impact on TTFF to fatal, permanent corruption of EEPROM code area on
the module (Please refer to “Power ONOFF Sequences and Power -On-Reset (POR)
on A2100-AB Application Notes”).
A controlled and orderly shutdown while the A2235-H is running in full power mode
can be initiated by
A 200ms pulse on the ON_OFF pin,
According messages either in NMEA or OSP mode.
The shutdown is completed after maximum 1s. Therefore the module should be
supplied with voltage for that time after the shutdown sequence was initiated.
This system is Powered from a computer, not a battery, so I have to way to shutdown the device before it is unluged (or laptop dies).
So when the GPS stopped, I though this must have been the issue, I must have accidentally unplugged it. I filed a ticket at the Maestro website, and they sent me this:
Dear Tim.
This device is a ROM only device, without any flash or corruptible firmware.
Please test the assess whether power consumption or signal level on the I/Os are OK.
It seems that the device may have possibly been physically damaged, otherwise, there should be no reason as to why it would not properly communicate.
So perhaps it is not from unplugging it. But I don't think anything has changed, so I'm not sure what could have broken it. But then I found this post on this forum:
AussieSusan:
I have used one of these chips on a completely different board (one of my own design) and it was very easy to connect to it and receive the NMEA sentences via the UART interface (which I used rather than the SPI internface).
However I feel I need to warn you of one very significant (in my opinion) issue with the Maestro family of GPS chips. My experience is that they are incredibly easy to break (internally) if you do not heed the data sheet comments about powering them down correctly.
In my situation I had the chip soldered to my PCB and therefore being powered up and down before I got around to programming the MCU that controlled it. In my haste, I programmed the initiation sequence and the UART reading part first and and was receiving location information OK. However I didn't have the part of the program that shut the chip down before the power was lost - and even while I was developing that part of the code, I had to turn the power off at various times whole the MCU was not running (i.e in debug mode or halted).
This fairly quickly broke the chip internally.
The symptoms were that the messages continued to be sent by the chip but the satellites that it said it could see were not actually in the sky, the S/N for all of them was reported as zero and no fix was ever obtained. In other words the chip outwardly appeared to be operating but was functionally useless.
The Maestro technical people were very helpful and provided me with a number of command lines to send to the device (basically to try to perform a complete reset and cold start) but nothing worked. In the end they asked if I could send the chip back to them but that would mean significant damage to the surrounding board and I didn't do this.
The bottom line is that these chips appear to be a good and cheap GPS device but you ABSOLUTELY MUST put them into the proper shutdown state prior to powering them down. This is stated in the data sheets:"Abrupt removal or drop of main power while the system is running has risks ranging from minor impact on TTFF to fatal, permanent corruption of flash memory code area on the module"
In my case it was fatal but I accept that it was my own fault. Please make sure the power down sequence is handled correctly for the Maestro GPS chips.
Susan
SO.. Now I am quite confused...
I have a few key questions:
1.) is my GPS broken, or can it be made to work again. (or is it not the GPS at all???)
2.) Long-term, do i need a battery backup? Or should I chose a better GPS for this project that does not die when power is removed. There will be more prototypes either way. What kind of GPS do you recommend? (low cost, low accuracy, low speed, very crude/basic will work fine.)
Any Ideas?
Thanks
Tim
