Speedtouch 121g on Raspberry Pi Zero


So I have the Raspberry Pi Zero working with ethernet, but it would be much nicer if this was also available via wifi. The only wifi stick I had left around was a Speedtouch 121g which internally is a Intersil ISL3887. Luckily I found the firmware for it.

My Pi Zero is running Dietpi 128 at the time of writing this blogpost, which after some fiddling around enabled me to have wifi setup. First, download the .arm file with the firmware and move it to the right direction. I have made a mirror here

Unpack it and move it with the “mv” command to /lib/firmware/isl3887usb. That is an L and not a 1. I made that mistake so it dit not work.

sudo mv /lib/firmware/isl3887usb

Unplug the wifi adapter and replug it. You can check if it is connected with the command

dmesg | more

And press enter until you see no warnings. Make sure you edit /etc/network/interfaces with the right network settings such as SSID and WPA2 password.
Or do it via the Dietpi config. Remind that the Speedtouch consumes quite some power. It might be best to not twist the connector and not fold it like I did on the picture as it happens to turn the adapter off. You might need to disable the wifi powermanagement in order to keep it working. As shown on the picture here, it drops after getting warm and losing power. It is better to use a powered hub as this adapter uses quite some power.

Big thanks to Domoticx for providing the instructions in Dutch.

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