I want to create a stop motion movie of sourdough growing over night. Don't ask. Since I'm very comfortable with the OS, I am using Raspberry Pi as the hardware platform. And since everyone will tell you that _Lighting_ is important for any kind of filmmaking I played around with ways to toggle power on the USB ports to control USB-powered lamps.
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The package `libusb-dev` is only one
```bash
sudo apt install libusb-dev
```
away. Luckily, Joel Dare (aka "codazoda") already wrote a handy program to access those C-bindings ((https://github.com/codazoda/hub-ctrl.c/blob/master/hub-ctrl.c)):
```bash
pi@sauercam:~ $ git clone https://github.com/codazoda/hub-ctrl.c
Cloning into 'hub-ctrl.c'...
remote: Enumerating objects: 13, done.
remote: Counting objects: 100% (13/13), done.
remote: Compressing objects: 100% (12/12), done.
remote: Total 62 (delta 3), reused 5 (delta 1), pack-reused 49
Unpacking objects: 100% (62/62), done.
pi@sauercam:~ $ cd hub-ctrl.c/
pi@sauercam:~/hub-ctrl.c $ gcc hub-ctrl.c -l usb -o hub-ctrl
pi@sauercam:~/hub-ctrl.c $ sudo mv hub-ctrl /usr/bin/
```
This will produce an ELF binary named `hub-ctrl` and place it in your path. Now let's figure out how the Raspberry Pi Model 1 B 2.0 (CPU Revision `000e`) and 2 Model B 1.1 (CPU Revision `a01041`) are structured wrt USB:
```bash
pi@sauercam-000e:~ $ lsusb -t
/: Bus 01.Port 1: Dev 1, Class=root_hub, Driver=dwc_otg/1p, 480M
|__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/5p, 480M
|__ Port 1: Dev 3, If 0, Class=Vendor Specific Class, Driver=smsc95xx, 480M
pi@sauercam-a01041:~ $ lsusb -t
/: Bus 01.Port 1: Dev 1, Class=root_hub, Driver=dwc_otg/1p, 480M
|__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/5p, 480M
|__ Port 1: Dev 3, If 0, Class=Vendor Specific Class, Driver=smsc95xx, 480M
|__ Port 2: Dev 5, If 0, Class=Hub, Driver=hub/4p, 480M
```
I know for a fact that the Ethernet card is connected via USB on the Raspberry Pi so for the B 2.0 we are probably out of luck: it only has one bus with one hub with one port. If we disable it to switch USB lamps off, we will also disable the Ethernet connection. For the 2 Model B 1.1 it looks a bit differently though: there are two ports available. Let's try the second one:
```bash
sudo hub-ctrl -b 001 -d 002 -P 2 -p 0 # re-enable with: -p 1
```
And now it's disco time:
```bash
awk -v n=10 -v seed="$RANDOM" 'BEGIN { srand(seed); for (i=0; i<n; ++i) printf("%.4f\n", rand() / 3) }' | while read amount; do sleep $amount; hub-ctrl -b 001 -d 002 -P 2 -p 1; hub-ctrl -b 001 -d 002 -P 2 -p 0; done
```
<img decoding="async" src="/wp-content/uploads/2020/09/disco.gif" class="aligncenter size-full" style="position:relative;border:4px solid #ddd;width:480px;height:270px;z-index:20;display:block" />
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