Solved "USB device is removed" problem

[slcasner]

I bought an HW180STB in 2016 that came with SW Version Jan 21 2016-03:52:18-V11.0. It worked fine since then for timed recording on a SanDisk Extreme USB 3.0 64GB flash drive. Then in August I unwisely updated to SW Version 11.3 because after that if the flash drive was plugged in before the unit was turned on then it would show "USB device is removed" and not be able to record or play back video. The flash drive would still work fine if plugged in after the unit was turned on.

I opened the HW180STB box to see if the USB connector had some problem. There was none, but I discovered that there are pads on the circuit board for the console serial port. Connecting there at 115200 baud I saw that the USB device negotiation was attempted and failing repeatedly if the flash drive was plugged in before power on, but proceeding successfully if plugged in later. So I worked around this problem with a hardware solution. I made a tiny circuit board that I soldered directly against the bottom side of the main circuit board underneath the USB connector to pick up the four USB wires. That PCB contains a tiny 6-pin microcontroller that holds the USB data lines in reset state while scanning the console serial output until it sees a string that indicates the system initialization has completed to the point where USB negotiation with the flash drive will succeed. My timed recording now works fine again.

hw180usb.small.png (226.48 KiB) Viewed 206 times

The photo shows my modification. The four pads with the label J1 are the USB wires. The green wire picks up the console serial line. The edge connector at the bottom is for programming the firmware into the microcontroller before soldering the board into place. Total cost for parts including PCB fabrication was under $2.