PC does not recognize the USB serial port after some days

[A_neves]

Hi everyone,

I developed a board that uses a FT2232D DUAL USB TO SERIAL UART to communicate with a Ubuntu PC.
The thing is, after some days, for example 1 or 2 weeks, the PC can not recognize the USB Serial Converter. To solve this I need to shutdown all the system for 5 seconds and power on again.
It is not easy to make debug, because this problem can take 2 days or 2 week to show up.
I am thinking if the problem could be about my PCB design. I am using 115200 Baudrate.
Could someone have a look on my schematic and layout?

Thank you!

[robertferanec]

If you need to turn off board and wait some time to discharge everything, the problem (or one of the problems) what you may have on the board is improper board initialization (e.g. reset, power sequencing, not working crystals, etc ...)

Notice, they have 4.7k pull up and 10k pull down on reset# signal. In your schematic, you only use 10k pull up - this could be one of the problems you are experiencing (your reset will stay high for some time until board is discharged).

PS: USB layout is also not ideal, but that would probably cause "only" connecting/disconnecting the device and not freezing it. USB signals are differential pair signals and ideally you would like to be routed them together, without stubs + they should follow 90OHM diff pair impedance (or keep them as short as possible if you use 2 layer PCB)

[A_neves]

Hi Robert,

Thanks for your answer.
Yes, after this problems I notice that my schematic it is different.
But the stranger thing is why the FTDI stays working some days, and for some reason fails? Could it be some floating on VCC at 10k pull up resistor?
I made that layout because I do not use reset pin on FTDI.
This system it is mounted on top of one fridge. I notice that the PC display blinks every time that the fridge motor starts, to cool-down the temperature.
I do not know if the power supply at my PCB adapter have some problem because of ​fridge motor current needs.

Thank you!

[robertferanec]

But the stranger thing is why the FTDI stays working some days, and for some reason fails?

- so, you are using the board everything is running fine and then suddenly after days of weeks it crashes or freezes or reboot (what exactly is happening)?

This is why I said "or one of the problems". The resistor may only solve the waiting problem (when you need to wait 5 seconds and then switch it on again). Crashing / Freezing / Rebooting is caused by different problems in design and these may be for example layout issue, EMC problem, crosstalk problem, power problem (noise, decoupling, filtering, ....), .... that is very hard to say.

PS: Fridge is the worse - it can generate pulses on Main and these pulses can cause interruption of devices (same is happening on my monitor - black out every time our freezer switch on/off). Still if your board would be well designed, it should survive the pulses - easy to test, move your board to different room (if possible) and you will see. But I suspect, the problem may be somewhere else - e.g. I would maybe try to filter the input power (maybe use and inductor or / and capacitor filter, possibly ferrite on usb cable, etc)

PS: Also I have seen many problems when grounds were connected through different mains (e.g. if you PC and your other device are connected in different main plugs, but these problems are usually much more visible, not just once a while).

[A_neves]

- so, you are using the board everything is running fine and then suddenly after days of weeks it crashes or freezes or reboot (what exactly is happening)?

Crashes, because the PC can not mount the Serial COM, but can see that there is anything at USB line, but can not mount.

I have 3 more systems like this, but only on at one that problem appears. I replaced my board, PC, USB cable, Power adapter and I am having the same problem.

The fridge is a really big problem. I measured the AC line and every time the motor Switch on/off changes the VPP to a lower value.
I am using a ferrite on USB cable, but I am getting the same problem.

I made a test. If I switch off my board, with all big capacitors and capacitors of power adapter, my board remains, near 2 seconds, working. But If I power on my board again with a delay near this 2 seconds after switch off, my PC can not recognize the USB Serial Converter.
I am using Net-ties to connect grounds, because I have another circuit to control 12V solenoids. But I soldered a jumper o have a better connection between grounds and the problem remains.

​Thank you Robert!

[robertferanec]

Crashes, because the PC can not mount the Serial COM, but can see that there is anything at USB line, but can not mount.

- so your board is occasionally disconnecting from your PC and does not connect back (stays like unrecognized device)?

If I switch off my board, with all big capacitors and capacitors of power adapter, my board remains, near 2 seconds, working. But If I power on my board again with a delay near this 2 seconds after switch off, my PC can not recognize the USB Serial Converter.

- this looks like the reset problem what can be fixed by the additional resistor (or possibly also + a discharge diode). Simply probe your reset signal and check what happens when you switch off the board. I suspect, the reset signal will not go into 0 so if you re-connect the power quickly, it will not reset the chip.

[A_neves]

- so your board is occasionally disconnecting from your PC and does not connect back (stays like unrecognized device)?

Yes Robert, this is what is happening.

​

this looks like the reset problem what can be fixed by the additional resistor (or possibly also + a discharge diode). Simply probe your reset signal and check what happens when you switch off the board. I suspect, the reset signal will not go into 0 so if you re-connect the power quickly, it will not reset the chip.

I tried using a wire jumper to force FTDI reset and the PC gets a USB disconnection. But after I release this jumper, the PC see something in USB line but still can not recognize the FTDI Serial converter.

[A_neves]

- this looks like the reset problem what can be fixed by the additional resistor (or possibly also + a discharge diode).

Robert, are you talking about using discharge diode on reset pin, or on +5V Vcc output?

Thank you!

[robertferanec]

discharge diode on reset pin, or on +5V Vcc output?

- reset pin. Have a look how we are doing it on 28pins: https://www.28pins.com/wp-content/up...matic-Page.pdf

"your board is occasionally disconnecting from your PC and does not connect back (stays like unrecognized device)" - Yes Robert, this is what is happening.

- this can be anything. As I described above "Crashing / Freezing / Rebooting is caused by different problems in design and these may be for example layout issue, EMC problem, crosstalk problem, power problem (noise, decoupling, filtering, ....), long / bad cable .... that is very hard to say."

I tried using a wire jumper to force FTDI reset and the PC gets a USB disconnection. But after I release this jumper, the PC see something in USB line but still can not recognize the FTDI Serial converter.

- interesting. After proper reset I would expect the device come up properly. I would probably try their original development board if that works properly.

[A_neves]

- reset pin. Have a look how we are doing it on 28pins: https://www.28pins.com/wp-content/up...matic-Page.pdf

Ok, I will have a look.

- this can be anything. As I described above "Crashing / Freezing / Rebooting is caused by different problems in design and these may be for example layout issue, EMC problem, crosstalk problem, power problem (noise, decoupling, filtering, ....), long / bad cable .... that is very hard to say."

I am using a USB cable with 1.5 m. This cable is next to 230VAC power supply and 5 USB Cameras. The only thing that stops working is my PCB.
I made some changes to produce a new test PCB. I add a few 0 ohm resistors to test.
I will try to power the FTDI from USB connector, test the reset conection from FTDI design guide. Also I am trying to have the FTDI more close to USB connector

- interesting. After proper reset I would expect the device come up properly. I would probably try their original development board if that works properly.

I have a breakout board with another FTDI model. I will make some tests to see if I am losing the connection too.

Could you have a look on my new design?

Thank you Robert!

[Paul van Avesaath]

'' I have 3 more systems like this, but only on at one that problem appears. I replaced my board, PC, USB cable, Power adapter and I am having the same problem. ''

did you swap your FTDI board? it looks to me that that pcb might just have some issues.. i don know if it is easy to replace, but if 3 other system do not show this issue.. i would suspect the board itself..

also you can add a line filter in your power connection for the fridge.. that can reduce the noise on your ac. those transients can be pretty anoying on components.. some times adding a ferride coil on you power connections can be enough to stabalize this power.. but i dont know how bad it is..

[A_neves]

''
did you swap your FTDI board? it looks to me that that pcb might just have some issues.. i don know if it is easy to replace, but if 3 other system do not show this issue.. i would suspect the board itself..

Yes Paul, I did. I am getting the same problem with another "copy" of my board.

''
also you can add a line filter in your power connection for the fridge.. that can reduce the noise on your ac. those transients can be pretty anoying on components.. some times adding a ferride coil on you power connections can be enough to stabalize this power.. but i dont know how bad it is..

I am using a ferrite on FTDI VCC. Or are you talking about ferrite coil on Power cable?

Thank you Paul!

[Paul van Avesaath]

i mean putting a choke coil on your power and or data cable.


also is there any mayor difference in location of your board then with the other setups? is the board that is going wrong working correctly on other locations?

[A_neves]

also is there any mayor difference in location of your board then with the other setups? is the board that is going wrong working correctly on other locations?

The difference is a plastic hood that covers all the system. The only heat source is the PC power supply.
Yes, if move the board to another locations works with no problem. But there are more space between board and other peripherals like PC and AC supply.

[robertferanec]

If any of your same boards close to the fridge is crashing, then the design is too sensitive ... or the fridge is too noisy. Play with filtering as Paul van Avesaath suggested (and as I suggested e.g. add LC filter after the USB connector). You may need to figure out if problem is caused by noise on power (filter the power) or noise on data (e.g. try very short cable) or by something else.