Cannot open COM port for FiPy and PyTrack

[Sat]

@robert-hh @seb

Sorry for the bullet 3: I had measured the voltage of pytrack without connecting FiPy. If I connect FiPy, 3v3 fluctuates between 1 volt and 2.1 volt and Vin fluctuates between 0.5 and 1 volt. I measured if using a simple multimeter. I do have access to a benchtop multimeter if you need to see the waveform over time. Let me know.

Any help will be highly appreciated. Thanks.

[robert-hh]

@sat That does not look well. Vin and 3.3V should get static readings of >4.5 V and 3.3 V. Looks like you have a power supply problem. Change the cable and/or the USB port of your computer.

[combaindeft]

@seb
@robert-hh
@Sat

I've had the same issue, and as I wrote in:
https://forum.pycom.io/topic/2338/pytrack-fipy-setup-on-win7/22
https://forum.pycom.io/topic/2338/pytrack-fipy-setup-on-win7/23

The only way I can get it work is:

1st) Connect only the PyTrack to usb
2nd) I get a usb-serial device
3rd) I then plug the FiPy device into the PyTrack ...
4th) Now I see the FiPy boot up and run the "pycom.heartbeat(True)" ... Led blinking blue ...

To re-cap, if I try to power on the FiPy+Track (combo) via usb, it doesn't even boot up (no Led blinking blue) ...

I also just tried it with a JST LiPo Battery (FiPy+PyTrack+Lipo-Battery combo) ... and now it boots up and I get a usb-serial...

So the odd thing is, why does it try to boot-up in DFU-mode when FiPy+PyTrack is connected?

But it boots as usb-serial-device when only the Pytrack is connected? or when adding a battery, FiPy+PyTrack+Battery ...

I find this a little bit of strange logic ... and It's a little bit odd ... and I do think there is some sort of issue in the Firmware code (pytrack_0.0.8.dfu)

Where might one find the Firmware code (pytrack_0.0.8.dfu)? ... so one might have an investigative look at boot sequence of the PyTrack :-)

[combaindeft]

@robert-hh

regarding it beeing a voltage issue.

as I wrote below, if I 1st boot up the PyTrack ... then I hot-swap the FiPy into the PyTrack ... it works ...

and when I do a:
print (py.read_battery_voltage())

I get the same reading of 4.45 --> 4.46 Volts.

I re-do the same experiment, with the FiPy+PyTrack+JST-LiPo-Battery combo ... this time around it boot with usb-serial and the FiPy boots up (too).

The readings I get then is: 4.43 --> 4.47

So there is no issue with voltage and such ... and the devices don't use that much Amps either ...

According to "System Information.app" the PyTrack is using:

Current Available (mA): 500
Current Required (mA): 500

And it uses the same amount no matter what combo (Pytrack, PyTrack+FiPy or PyTrack+FiPy+Lipo-Battery ...)

IMHO, there is no "Power issue" ... but rather a Firmware code (pytrack_0.0.8.dfu) issue ...

[robert-hh]

@combaindeft For me it still looks like a power supply problem, especially since attaching a LiPoy battery helps. If you did not do that yet, try another short & good USB cable and/or a different USB port on your computer, preferably a USB3 port.
The power drops could be transitional. The current consumption of the devices vary a lot.
Still it could be problem in the PyTrack board.

[combaindeft]

@robert-hh

The logic that I can 1st boot up the PyTrack ... get a usb-serial port ... then I hot-swap in the FiPy ... the FiPy boots up ... means there is enough voltage / current for it to boot up ...

Why the issue dissapears when I attach the LiPo Battery, and get a usb-serial (too) is key.

As, I also get a usb-serial if only I boot up the PyTrack (just the PyTrack) ...

I'm very much leaning toward a firmware issue ... in the boot sequence of the PyTrack when it checks how it wants to boot up .... in DFU-mode or USB-Serial mode ...

As we've just proven that it boots up with USB-Serial in two Combo's ... but not in the 3rd ...

PS ... also, I've changed multiple usb-cables, Ports and even other Mac computers ... still the same issue. And also, yeah, it's USB3.0 ports I've tried it on...

[nathanh]

@combaindeft said in Cannot open COM port for FiPy and PyTrack:

@robert-hh

The logic that I can 1st boot up the PyTrack ... get a usb-serial port ... then I hot-swap in the FiPy ... the FiPy boots up ... means there is enough voltage / current for it to boot up ...

Why the issue dissapears when I attach the LiPo Battery, and get a usb-serial (too) is key.

Actually what @robert-hh is saying lines up rather than your logic. Booting 2 devices together at the same time will have a much higher current spike on boot up rather than powering one device then the next as after the initial boot current draw will drop. Also a lipo battery can supply more current than a standard usb port. For instance most 3g/ lte modems spike above 500ma on send and can fail when using a usb port on their own.

Again you could be right and it's not an issue but the symptoms you're seeing with the fix you have point towards a current or voltage issue.

[combaindeft]

@nathanh
@robert-hh
@seb
@Sat

@seb

A) FiPy+PyTrack+LiPo-Battery (Not-Attached-to-USB3.0)

Vin = 4.09~4.10 V
3V3 = 3.32 V

B) PyTrack+USB-Serial-device (Attached-to—USB3.0)

• same port as A)

  Vin = 4.85 V
  3V3 = 0.23 V

C) PyTrack+USB-Serial-device (Attached-to—USB3.0) + Hotswap-in-FiPy

• same port as A) & B)

  Vin = 4.55 V
  3V3 = 3.32 V

D) PyTrack+FiPy+NO-USB-Serial-device (Attached-to—USB3.0)

• same port as A) & B) & C)
• same combo as C)
• Just unplugged USB from PyTrack, and re-attached it…

  Vin = 1.69~2.51 V
  3V3 = 1.15~1.91 V

- Also, worth nothing is that if my hand slips with the measuring probes, I get it to “boot-up” by accidentally shorting GROUND & 3V3, and I get a USB-Serial-Devices on my computer [ergo like A), B) & C) …] …
- And then, I get the same Vin & 3V3 as C)
- Which makes me conclude that you’ve guys have a Firmware issue!!! … and not a “bad usb-cable” or “bad usb-port” … etc etc.
- For some reason, in the boot-sequence of the PyTrack Firmware, it choose not to boot-up FiPy and enable USB-Serial …
- And, again, it’s odd that I can short GROUND & 3V3 with my measuring probes, and then it boots up FiPy and enables USB-Serial…

[robert-hh]

@combaindeft
B) is clear, since the 3.3 regulator is on the FiPy device. Without that, no power at the 3.3V pin.
Due to A) with the rock solid supply through a battery it is hard to accept, that it's a firmware issue, at least of the FiPy. Still, the PyTrack board can be the culprit. Did you try to run the FiPy without the PyTrack board, like on a breadboard with a separate USB/serial interface?

Shorting 3.3 and GND should be avoided.
P.S.: It's a pity that Pycom does not publish schematics.

[AJCazz]

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