Issue with FTDI adapter on a short 1M lead

Hello all, just wondering/hoping someone may have seen this before. I have a serial device with an embedded FTDI chip on an approx ~1 meter USB cable from the Balena Fin. It is recognized when connected and ttyUSB0 is established as you would expect however there’s no comms to/from the serial device.

Here’s the weird part… If I add a 3 meter USB extension cable the tty is added AND the device works?!

Looking for ideas on what to look at next and what might be the missing piece to getting the device running locally on its short cable???

dmesg log below when used on short cable fyr:
[Tue Oct 22 07:55:33 2019] usb 1-1.5: new full-speed USB device number 7 using dwc_otg
[Tue Oct 22 07:55:34 2019] usb 1-1.5: New USB device found, idVendor=0403, idProduct=6001, bcdDevice= 6.00
[Tue Oct 22 07:55:34 2019] usb 1-1.5: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[Tue Oct 22 07:55:34 2019] usb 1-1.5: Product: FT232R USB UART
[Tue Oct 22 07:55:34 2019] usb 1-1.5: Manufacturer: FTDI
[Tue Oct 22 07:55:34 2019] usb 1-1.5: SerialNumber: AI05IGYT
[Tue Oct 22 07:55:34 2019] ftdi_sio 1-1.5:1.0: FTDI USB Serial Device converter detected
[Tue Oct 22 07:55:34 2019] usb 1-1.5: Detected FT232RL
[Tue Oct 22 07:55:34 2019] usb 1-1.5: FTDI USB Serial Device converter now attached to ttyUSB0

I should also add that the problem only occurs on Balena Fin. x86, RaspberryPi, Odroid etc all work as expected without issue.

Testing is done using ‘minicom -D /dev/ttyUSB0 -b 115200’ (8,n,1 & no flow control).

@nzbypaul hey there! Just interested to know a couple of things:

  1. What Fin revision are you using? (v1.0 or v1.1, or even better the revision of the board printed on the PCB)
  2. Are you using the USB port or the header pins on the board (if 1.1)?
  3. When you say ‘USB extension’, are you continuing to use the 1 metre cable then adding the 3 metre extension to give a total of 4 metres, or swapping the 1 metre cable out for a 4 metre one?

Also, not suggesting it’s relevant here but something to be aware of; the Fin 1.0 has one of these FTDI chips on the board. I’ve had software unable to select the correct interface when two devices are plugged in simultaneously before.

Hi @chrisys thanks for your reply.

  1. We are using Fin v1.1.
  2. Both the header and USB are not working but so far I haven’t had access to a longer cable to check if the header issue is resolved with an extender cable as with the USB port.
  3. The same cable is used and a 3 meter USB extension cable is ‘added’ to this

I’m not sure of where on the board the the printed PCB version is shown, can you advise?

Also worth mentioning is the compute module ‘Raspberry Pi Compute Module 3 Rev 1.0’

@nzbypaul the board revision is part of the copper layer on the PCB just above the GPIO header (it’s black on black so is a little hard to see), as you’re on a v1.1 it’s not so important.

I chatted with a couple of the Fin engineering team and the only thing we can think of is that the 1 meter cable is not making good connection with the ports (we’re assuming you’ve tried both ports), and by using the extension you’re effectively using a different connector which works better.

It would also be beneficial if you could provide us with a photograph of the setup if at all possible - just so we can see what the cables and adapter look like.

There’s really no technical reason why this should be any different between a Pi and the Fin so we’re interested to figure out what’s happening.