Hello!

I'm trying to setup softserial to use GPS on an iflight Succex-D whoop AIO 20A, like the one in the link below.  It came from an iflight alpha a75hd that I disassembled and used components for other builds.

https://www.getfpv.com/iflight-succex-d-...u6000.html

The LED pad can be used as one of the rx/tx pair for softserial.  I've freed that resource from LED_strip and then assigned it as serial_tx 11.  Actually it was odd that with default settings (not from factory, I already re-flashed this one at some point) that resource (A08) was initially assigned as both LED_strip and as serial_tx 11.  Regardless I freed it from LED_strip, so now it's just serial_tx 11.

Now for serial_rx 11, I examined the board and there seems to be a mini pad that goes directly to the third pin from the left of the processor along the top row, if the lettering on the chip is up.  I'm trying to figure out which pin this would be on the chip itself.  This is one part that I'm wondering if anyone can help with.  I've searched and found what I think is the pinout of this processor - written on mine is "STM32F411CEU6740H101".  This is what I think is the pinout, found in this website:

https://www.datasheets.com/en/part-detai...s-56910630





This image shows the orange wire that I'm hoping can work for this, connected to a pad on the top row, third pin from the left.  





First, can anyone help confirm if I've found the correct pinout diagram for my processor, and also which way the diagram is oriented relative to the actual component on the board?  I thought at first that the lettering goes upright on the diagram to match the processor, then was wondering if the dot indicates pin 1 as often it does on electronics.  Then I also found this thread which is about the same processor, and from there it seems to indicate that A14 might be on the left edge near the top.

Here is that thread from rcgroups:

https://www.rcgroups.com/forums/showthre...trip-fixed


Thanks for any replies or advice!

I got it working!

From the rcgroups thread I posted, it mentions that A13 does not work as RX on this chip.

Turns out that A13 is the pin of that mini pad on my FC, along the top row 3rd from the left, with the orange wire.

Also, the diagram I found seems to be correct, and pin 1 is near the dot.



So anyway, once I set it up so A13 was the softserial tx pin, and the pin that used to be LED is now softserial rx (a08), GPS works!

That is the correct pinout if you have the 48 pin package which it looks like you do. The pin 1 marker is the smaller/deeper indentation (sometimes there are multiple other times it can be worn off) but the lower left corner when reading the letters seems to be correct. In this case top row third pin from the left would be pin 34 or A13. If that pin is mapped on your board, you can check for continuity if there is a respective solder pad.
Also if you can probe the pins, you can confirm the orientation by doing a continuity check on the VSS or VDD pins. They are located on 3 of the 4 sides (first 2 pins) and you should get continuity on all sides except for the pin 1 side of the chip.

(07-Aug-2023, 09:40 PM)mstc Wrote: That is the correct pinout if you have the 48 pin package which it looks like you do. The pin 1 marker is the smaller/deeper indentation (sometimes there are multiple other times it can be worn off) but the lower left corner when reading the letters seems to be correct. In this case top row third pin from the left would be pin 34 or A13. If that pin is mapped on your board, you can check for continuity if there is a respective solder pad.
Also if you can probe the pins, you can confirm the orientation by doing a continuity check on the VSS or VDD pins. They are located on 3 of the 4 sides (first 2 pins) and you should get continuity on all sides except for the pin 1 side of the chip.

Thanks! Good to know for future reference.

Please let us know how this works out.

In general, a GPS is often "sketchy" on SoftSerial.

Does your craft have analog or digital video?

For analog setups, the SmartAudio can be put on the SoftSerial and the GPS on a hard UART.

Evidently on digital setups, the Video needs to be on a hard UART so people put the GPS on
SoftSerial. Another member is in the process of doing this as we speak. His set up is having
issues just getting enough SATs and SAT fix is pretty slow at about 5 minutes.

(08-Aug-2023, 12:37 PM)iFly4rotors Wrote: Please let us know how this works out.

In general, a GPS is often "sketchy" on SoftSerial.

Does your craft have analog or digital video?

For analog setups, the SmartAudio can be put on the SoftSerial and the GPS on a hard UART.

Evidently on digital setups, the Video needs to be on a hard UART so people put the GPS on
SoftSerial. Another member is in the process of doing this as we speak. His set up is having
issues just getting enough SATs and SAT fix is pretty slow at about 5 minutes.

Hello,
Mine has a digital vtx - caddx vista, and along with the crossfire nano Rx my two uarts are taken unfortunately.

I only did an initial power up to verify that it works and picked up about 5 satellites, then I turned it off.

I'm also curious to see how well it works, as I remember reading one of Oscar Liang's articles recommending not to use softserial for gps. But then in Dave C's thingiverse page about his micro long range project, he mentions using softserial for gps.

I'll post back here once I've finished re-soldering a few connections and re-assembling the quad.

Hi Marcelo,

I have always followed the convention of putting the GPS on a hard UART.

Yes, you can put the GPS on SoftSerial which I am sure "technically" will
work. During flight, satellite data is updated continuously, but how fast.   
So, what do you expect from the GPS. If you just want distance and that little
arrow pointing toward the transmitter, well, that is one thing. Slow satellite 
data updates may not matter that much.  

On the other hand, if you want the "Failsafe" option to work, the question is: 
Will it?? So, you get 8 SAT fixes and takeoff. On a "slow" connection the GPS
will update, well, slowly. If the GPS doesn't keep up with the quad, will the 
"Failsafe" actually work correctly? Or...will the quad be outrunning the SAT
location updates. Wonder how this works for Failsafe. 

Just thinking 

Maybe Dave C just needed the distance since he is a long range guy. 

(08-Aug-2023, 08:18 PM)iFly4rotors Wrote: Hi Marcelo,

I have always followed the convention of putting the GPS on a hard UART.

Yes, you can put the GPS on SoftSerial which I am sure "technically" will
work. During flight, satellite data is updated continuously, but how fast.   
So, what do you expect from the GPS. If you just want distance and that little
arrow pointing toward the transmitter, well, that is one thing. Slow satellite 
data updates may not matter that much.  

On the other hand, if you want the "Failsafe" option to work, the question is: 
Will it?? So, you get 8 SAT fixes and takeoff. On a "slow" connection the GPS
will update, well, slowly. If the GPS doesn't keep up with the quad, will the 
"Failsafe" actually work correctly? Or...will the quad be outrunning the SAT
location updates. Wonder how this works for Failsafe. 

Just thinking 

Maybe Dave C just needed the distance since he is a long range guy. 

Hi iFly,
Good points, and I'm hoping for the best but would be content with just some basic gps functionality like the home arrow, and maybe some crash site coordinates that I hope I'll never need

Perhaps for a failsafe scenario as you described it would help to decrease the rth flight speed.

For RTH, I need to first update from BF 4.3 to 4.4 to take advantage of all of the improvements in that function.