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Tweaking the Logitech R400 presenter tool on Linux

This article is a updated version of an earlier one, which describes how to tweak the R400 on non-systemd systems.

In 2002, I received a Logitech R400 presenter tool for Christmas as a replacement for the php|architect pointer that has now fallen apart. However, to use it together with my presentation systemβ€”pres2, about which I previously wroteβ€”I need it to provide left and right arrow keypresses. By default its left and right buttons generate Prior and Next events in X. It took me a while to get this to work, so in short, this article sets out how I changed it.

First of all, I editted the file /lib/udev/hwdb.d/60-keyboard.hwdb as root. I searched for R400 and changed its entry to:

# Logitech Presenter R400
keyboard:usb:v046DpC52Dd*dc*dsc*dp*ic*isc*ip*in00*
 KEYBOARD_KEY_070029=f11
 KEYBOARD_KEY_07003e=f11
 KEYBOARD_KEY_070037=f5
 KEYBOARD_KEY_07004b=left
 KEYBOARD_KEY_07004e=right


This maps the two scan codes that the Play button (lower-left) generates to f11, the empty screen button to f5 and the left and right buttons to the left and right arrow keys.

The first column represents the scancode, which I obtained by first looking up with input event the device was tied to:

stat -t /dev/input/by-id/usb-Logitech_USB_Receiver-event-kbd --printf "%N\n"

Which showed the following for me:

β€˜/dev/input/by-id/usb-Logitech_USB_Receiver-event-kbd’ -> β€˜../event19’

To find out the scan codes, I had to download a getscancodes tool, and then compile it:

wget 'http://downloads.sourceforge.net/project/keytouch/getscancodes/getscancodes%201.0/getscancodes-1.0.tar.gz?r=http%3A%2F%2Fkeytouch.sourceforge.net%2Fdl-getscancodes.php&ts=1412723944&use_mirror=kent' -O getscancodes-1.0.tar.gz
tar -xvzf getscancodes-1.0.tar.gz
cd getscancodes/
make

With the new binary, and the event19 from above, I ran:

sudo ./getscancodes /dev/input/event19

Which showed:

458807 (0x70037)
458793 (0x70029)
458814 (0x7003e)
458827 (0x7004b)
458830 (0x7004e)

With these numbers, I now had enough information to edit the /lib/udev/hwdb.d/60-keyboard.hwdb file that I mentioned earlier.

After that, I had to run:

sudo udevadm hwdb --update

This consolidated the modified rules and made the keymapping active. My presenter tool now sends the correct key codes again.

The changes will persist after rebooting as well.

Shortlink

This article has a short URL available: https://drck.me/r400-b4d

Comments

My 60-keyboard.hwdb had evdev:input:b0003v046DpC52D* in it. Did you have that before your edits or did you have keyboard:usb:v046DpC52Dd*dc*dsc*dp*ic*isc*ip*in00*

One other thing which may be of interest. My old presenter went walkies, and I bought a new one which looks the same, but its USB ID is 046d:c538, not 046d:c52d. You might want to make a note about this to help people who find your web page but don't understand the significance of the string in (either your or my version of) 60-keyboard.hwdb.

Cheers.

One other thing. I believe the politically correct thing to do is not to edit the file in /lib, but to put your definition in a file in /etc/udev/hwdb.d/60-keyboard.hwdb

I tried that and (after running udevadm hwdb --update as you say) it works on my system.

Q: if you have the image of the R400 visible on your screen and you look away a bit, does it look like Darth Vader to you? ;-)

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