Control USB-powered devices with a Raspberry Pi
Power Point
Command-line tools and Node-RED on a Raspberry Pi let you control projects that use the USB ports.
For home automation projects, a Raspberry Pi offers a simple, low-cost approach to managing and controlling a wide variety of devices. Typically these devices are either digitally wired 0-5V devices such as motion detectors, or wireless Ethernet devices such as smart plugs. It's important to note that a Raspberry Pi can also control USB-powered devices, such as USB fans, lights, and low-end controllers.
In this article, I look at how to monitor, control, and measure USB power in two Raspberry Pi projects. The first project uses Node-RED to create a web dashboard to monitor and control USB lights. The second project turns on USB cooling fans according to the Pi's CPU temperature.
Controlling USB Ports
A number of techniques allow you to control USB ports, and I found that one of easiest approaches is to use the uhubctl
[1] utility, which lets you view and control local USB ports and ports on smart USB hubs. To load this utility, enter:
sudo apt-get install libusb-1.0-0-dev git clone https://github.com/mvp/uhubctl cd uhubctl make sudo make install
Figure 1 shows the output on a Raspberry Pi 4 with no USB devices connected. The Pi 4 has two internal USB hubs: Hub 1 connects to all the USB ports with the USB 2.10 standard, and hub 2 controls all the ports with the USB 3.00 standard and the Ethernet jack.
For the Raspberry Pi 3 and 4, the power on all USB ports is ganged together through port 2, so unfortunately it is not possible to power up and down an individual USB port.
The commands to turn on or off or toggle the USB ports and keep the Ethernet jack powered are:
sudo uhubctl -l 1-1 -p 2 -a on sudo uhubctl -l 1-1 -p 2 -a off sudo uhubctl -l 1-1 -p 2 -a toggle
These commands return messages showing the current status, the power requested state, and the new status.
Monitoring USB Power
The uhubctl
command lets you check the status of Pi port 2, the ganged power port (Figure 2). With some Bash statements, the power status is parsed to show just the off or power message. The Bash statement
$ sudo uhubctl | grep 'Port 2' | awk '{print $4}' off
shows the power status on a Node-RED dashboard.
Node-RED USB Control Dashboard
Node-RED [2] is a visual programming tool included with the full desktop Raspberry Pi install. If Node-RED has not been installed, see the online docs [3].
A number of low-cost USB lighting options can be used with a Raspberry Pi (Figure 3), including LED strips, wire lights, and small USB lamps. Node-RED doesn't have a node to monitor or control USB power, but Bash commands can be used directly in Node-RED.
A simple Node-RED dashboard can be created to turn Raspberry Pi USB ports on and off and check the status of power on these ports. The logic (Figure 4) would include two dashboard button nodes, one dashboard text node, and two exec nodes. The uhubctl
utility can be used directly in the exec nodes.
The first exec node contains the Bash command to turn the USB ports on or off (Figure 5). The on or off string is sent from the dashboard buttons as a msg.payload
message that is appended to the command in the exec node. The output from the first exec node triggers the second exec node to get the latest USB port status.
The USB power status message can be made more presentable by editing the Value format field in the dashboard text node. For this example, I used an <h1>
heading and uppercase
formatting (Figure 6).
Once the logic is complete, the Deploy button on the right side of the menubar will make the dashboard available to web clients at: https://raspberry_pi_address:1880/ui. For this project, I added an enhancement to include a countdown or sleep timer (Figure 7).
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Support Our Work
Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.
News
-
Canonical Bumps LTS Support to 12 years
If you're worried that your Ubuntu LTS release won't be supported long enough to last, Canonical has a surprise for you in the form of 12 years of security coverage.
-
Fedora 40 Beta Released Soon
With the official release of Fedora 40 coming in April, it's almost time to download the beta and see what's new.
-
New Pentesting Distribution to Compete with Kali Linux
SnoopGod is now available for your testing needs
-
Juno Computers Launches Another Linux Laptop
If you're looking for a powerhouse laptop that runs Ubuntu, the Juno Computers Neptune 17 v6 should be on your radar.
-
ZorinOS 17.1 Released, Includes Improved Windows App Support
If you need or desire to run Windows applications on Linux, there's one distribution intent on making that easier for you and its new release further improves that feature.
-
Linux Market Share Surpasses 4% for the First Time
Look out Windows and macOS, Linux is on the rise and has even topped ChromeOS to become the fourth most widely used OS around the globe.
-
KDE’s Plasma 6 Officially Available
KDE’s Plasma 6.0 "Megarelease" has happened, and it's brimming with new features, polish, and performance.
-
Latest Version of Tails Unleashed
Tails 6.0 is based on Debian 12 and includes GNOME 43.
-
KDE Announces New Slimbook V with Plenty of Power and KDE’s Plasma 6
If you're a fan of KDE Plasma, you'll be thrilled to hear they've announced a new Slimbook with an AMD CPU and the latest version of KDE Plasma desktop.
-
Monthly Sponsorship Includes Early Access to elementary OS 8
If you want to get a glimpse of what's in the pipeline for elementary OS 8, just set up a monthly sponsorship to help fund its continued existence.