I have a full speed USB audio device connected to the USB port on a SBC running Ubuntu Linux. I'm acquiring data over this connection and I need 24/7 uninterrupted data acquisition. If the USB connection drops at all then I lose data since the device has no NVM and is powered via USB VBUS.
I have 20 of these systems deployed in a typical North American urban environment, in the rear yards of residences, away from any obvious EMI sources. Over the course of 2 weeks of data collection I've had 2 momentary USB dropouts (lasting < 1 second).
The SBC I'm using is this one and it exposes the USB host interface as four male header pins. I have a custom 6' USB cable which connects to the device using microUSB-B and at the host end has a 1" length of breakout to female headers. For this final inch there is no shielding and no twist in the data conductors. The drain of the USB cable is connected to a ground pin on the SBC. Neither the USB host nor USB device has a metal enclosure. The USB connections and all electronics are all well protected from water/dust ingress.
Prior to connecting the drain to ground I had a much higher rate of dropouts.
- Is there anything about the arrangement described that jumps out as a red flag as likely responsible for these dropouts?
- Is the dropout rate I'm experiencing expected for a typical USB system? I've never noticed USB dropouts in my day-to-day life with USB (e.g, using a mouse, keyboard, webcam, etc) but I don't use USB for activities that would notice this drop rate.
- Is it reasonable to assume, since the port is exposed as header pins instead of a female USB-A port, that the SBC manufacturer expects the user to add additional circuitry after the headers and before the physical USB port? What would that typical circuitry be?
- Following on #3, would the SBC manufacturer likely not have implemented onboard EMI and/or ESD protection, and would users be wise to implement their own using something such as this device? I was informed by the USB device manufacturer that USB Implementers Forum does not recommend adding any passive network on the line and as such their USB device does not have any filtering. Yet filters like the Wurth unit I linked presumably exist for good reason. I've read this excellent answer yet I'm still unclear if this filter falls under the solutions identified as "flawed".