USB hub – per port power switching – an interim report.

Sometimes it happens, that my ZTE MF831 LTE stick, gets stuck somehow. It’s device id changes to something else, then documented in my other articel on this stick: ZTE MF831 for use with OpenWRT: serial modem instead of cdc_ether.

Usually, when that happens, only a full power cycle or unplugging and replugging helps.

Since none of my routers is capable of completely shutting down an USB port, there are only two possible solutions besides of using a timer clock, just in case.

a) to tinker with a relay or a transitor circuit, that will switch off the usb hub with it’s external power supply, when the usb port is shut down in software, alternatively use GPIO from your router

b) to get a PPPS USB Hub – a per port power switching hub already has builtin transistors for each of its port. If the hub chip supports PPPS, it will shut down a port completely, when software – like uhubctl signals it to do so.

But PPPS Hubs aren’t easy to identify and there is only a small number of products featuring PPPS.

The tool uhubctl supports some of these. Amongst them is the AmazonBasics USB Hub, 3.0 with 7Ports (Europlug and 12V/3A power adapter). Forget about the older D-Link DUB-H7 if, you don’t already possess on of the older silver cased version. The never revisions above 2.0 don’t support PPPS any longer.

You can find a list of uhubctl-compatible hubs here: https://github.com/mvp/uhubctl/blob/master/README.md

At the time I started searching for such a hub in september 2017, the model from Amazon Basics was the only one, that was really shipable. In the meanwhile there is also a model from TP-Link, the TL-UH700, but I haven’t yet analyzed that model. Also there is no hint given in the specification.

I have done some experiments with the Amazon Basics Hub connected to my TP-Link TL-WR1043ND v1 running OpenWRT. Unfortunately, while the switching of the ports worked well, a complete reset of the ZTE MF831 wasn’t possible. It seemed to still get enough current to remain in it’s locked up mode, which I guess, is Fastboot (or a similar) real download mode.

For other USB devices the PPP switching will work well. You can shut down a harddisk after use or switch an USB-LED or USB fan… Sounds like USB fun.

As soon as I find the time, I’ll resume my tests with a TP-LINK TL-WR1043NDv2 or a TP-Link TL-WR1043N v3.

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