raspbian – Page 4 – Kev's Development Toolbox

June 12, 2016

Raspbian USB disconnects and USB keyboards

I was looking for a solution to a USB soundcard that would randomly disconnect from my Raspberry Pi (it’s a Signalink USB soundcard/radio interface for amateur radio). Turns out, the issue I was seeing was caused by RF getting into somewhere when my radio was keying up – when I moved the HT radio further away from the Pi (only as far as the length of the connecting cable, a few feet) then my problems stopped. This could probably be avoided better with some snap-on ferrite beads.

In this post (and others), there is a suggestion about adding dwc_otg.speed=1 to your /boot/cmdline.txt. I tried this for a while and this didn’t seem to make any difference to my USB disconnects for this particular USB soundcard. It did however stop a USB keyboard from being recognized (a Gear Head Mini USB). Remembering I had added this param and then removing it solved my keyboard issue.

Lesson learnt: if trying out solutions to problems by trial and error, if something doesn’t work, remember to remove it afterwards in case it breaks other stuff 🙂

June 8, 2016

Resolving SSH laggy responsiveness over Wifi on Raspberry Pi / Raspbian

It’s interesting to note that turning off the power saving features for the common Wifi dongle chipsets used on Raspbian seems to fix not only the pauses where before it would sleep during inactivity, but also it seems to fix/improve the laggy responsiveness even when typing commands over SSH to a Pi. Links to the settings in my previous post here.

June 1, 2016October 30, 2018

Changing the brightness on the Raspberry Pi 7″ touchscreen (v1.1)

Per discussion here, if you have a v1.1 version of the Raspberry Pi 7″ touchscreen, you can vary the brightness by setting a value of 1 to 255 into the file /sys/class/backlight/rpi-backlight/brightness

Use sudo to echo values to a file, do:

sudo sh -c "echo 80 > /sys/class/backlight/rpi_backlight/brightness"

May 28, 2016

Fixing unresponsive touch on PiTFT with PyGame

I have a 2.8 PiTFT which I’ve used on my Pi 1 and just set it up on a Pi 2. I tried to get Adafruit’s FreqShow working with the screen, and it would display, but was unresponsive to any touch inputs. I know touch was working in X Windows otherwise, and had ran through all the calibration tools in the PiTFT setup instructions, so something else was wrong.

Some Googling later, turns out the PiTFT and PyGame (used by FreqShow) works ok on Raspbian Wheezy (which I have on my Pi 1), but not on Jessie (which I have on my Pi 2).

Trick is to replace libsdl with the prior/older version from Jessie – a script to do the replacement is in the post linked about. Ran the script, and now FreqShow works on the PiTFT 2.8 great. Shame there’s no audio out as well, but a cool use for the small screen.