A headless Raspberry Pi creates a web server that allows multiple users to control a robot. Users can control motors, speak using a speaker, and view a webcam.
Control a Raspberry-Pi-powered robot over the Internet or over any network via a WebSocket. See the webserver folder. I use pigpio to control a servo motor and motor driver via Raspberry Pi's pins, including hardware PWM on GPIO12 and GPIO13. I use child_process to speak via espeak and USB speakers. Install espeak via: sudo apt install espeak . I also can display video from a webcam. The first step to setting up a webcam server is installing motion via: sudo apt install motion .
The Raspberry Pi will run Node.js code. Install Node.js and required modules via...
sudo apt install nodejs npm
npm install socket.io
npm install pigpio
Run it via: sudo node webserver.js . Note that pigpio, halt, and reboot require sudo. I recommend using systemctl to start the code at startup (sudo is then not needed before node since systemctl is run as root). You can also automatically start the motion server via systemctl.
Once the code is running, just type the Pi's IP address into the web browser of any device that has access to that IP address! The following should appear...
Nice features...
- When one user moves a slider, the slider moves for all users.
- The vertical slider automatically goes back to the middle when you are no longer holding it.
Fixing various connection issues...
- If you don't have access to the router, things might still work on a local network. On Google Chrome, if http://raspberrypi.local works on at least one device, you can find the Pi's IP address by going to chrome://net-internals/#dns . If that doesn't work, I installed a free Android app, WiFiman, that, for devices on the same WiFi network, lists names (such as Raspberry Pi) and their IP addresses via its Discovery tab. I believe you can get this app on Apple too.
- If the webcam never shows on other devices, find the line stream_localhost on in /etc/motion/motion.conf, change on to off, then restart motion.
- If the webcam doesn't work on Google Chrome when using raspberrypi.local and the webcam never works when using the IPv6 address, find the line ipv6_enabled off in /etc/motion/motion.conf, change off to on, then restart motion.
- In /etc/motion/motion.conf, I also had to set both the framerate and stream_maxrate to 15 for the video not to have a huge lag. Setting ffmpeg_output_movies to off can also be smart so that videos aren't saved on the Pi.
- If you are connecting a computer to the Pi via a phone's hotspot and the connection is finicky, try unplugging the computer's Ethernet cable!
In the code, I have commented out initially calling setGPIO(). The servo would sometimes keeping spinning as if I was giving it a longer than 2 ms on signal for PWM. The problem was that, on startup, my code was set to run automatically be systemd (with After=network.target setting), and the PWM would start correctly when setGPIO() was called, but then there would be a final quick pop on the speakers and the PWM would permanently start to get a too low frequency (measured by oscilloscope), and there would be nothing short of sudo systemctl restart webserver that could reset the frequency, though perhaps calling pigpio's configureClock() in the code would fix it? A fix is to not run setGPIO() or interact with the robot at all until the pop on the speakers is heard, so I commented out the setGPIO() that occurs when the code starts. If the PWM is first used after the pop, then everything is good! Another fix could be to figure out systemd to make the webserver start later! Let me know what you figure out! If your motors do weird things before setGPIO() is called, please uncomment it!
The Node.js code runs a servo motor that connects to a geared DC motor to control the front wheels. As long as you only are controlling a single servo motor and a single DC motor, I expect the code to work just fine as is, though different DC motor drivers can require modifications to the code. The hardware we used...
- Raspberry Pi 3B, which has WiFi and two hardware-PWM channels
- access to the router to (1) give the Pi a static IP address and possibly to also, if you are wanting to allow control from the Internet, (2) direct inbound traffic to the Pi. If you only want to control it via a local network and want the freedom to move to various locations, you can use a smartphone's hotspot as the router then use the phone to find the Pi's IP address. I don't think it works on all devices or perhaps even all routers, but I can sometimes connect to the Pi without needing a static (knowable) IP address by using raspberrypi.local as the location.
- S05NF STD servo motor. This one is nice because it does nothing if the PWM signal is either always low or always high. 3.3V or 5V work nicely for the signal pin.
- If 3.3V doesn't work nicely for the signal pin of your servo, try creating a small circuit to change the 3.3V PWM to 5V: https://electronics.stackexchange.com/questions/359994/amplify-pwm-signal-from-exactly-0-3-3v-to-0-5v/360046#360046. Play around with resistances to get the correct low and high voltages being careful not to put any resistance smaller than around 330 ohms. Using a cheap level shifter, a SN74AHCT125N (well documented by Adafruit), instead of the small circuit will work much better! You cannot just use any level shifter because the PWM wire of the servo motor draws some current, and this one is good.
- DRV8833 motor driver. Adafruit sells one in a nice breakout board. This one has MOSFETs as its transistors, so it works well with our 5V motors.
- dual-shaft geared DC motor with a wheel attached on each side. An L bracket (from Adafruit) was used to connect it to the servo motor.
- $13 USB speakers from Amazon. The Node.js code can easily be changed to use non-USB speakers, but USB speakers are great because they are powered through the USB!
- $5 USB webcam from Amazon
- Ayeway PD-2620W battery pack. The 26,800 mAh capacity is way more than we need, and we only used the 5 volts from any of the 3 blue USB ports, which have a 3-amp-total maximum. USB cables were used to power things. The cables can be spliced to more convenient wires that are thick and short enough to carry requires current. Grounds between USB cables were connected on a mini breadboard (the same one that had the DRV8833 and SN74AHCT125N) to create a common ground. The Raspberry Pi initially got a dedicated USB cable to power it (motors were powered from another cable from the same battery). Even so, when the DC motor was stalled or was not allowed to spin freely, the battery was likely delivering approximately its 3-amp limit, and the Raspberry Pi would not get enough voltage causing the webcam to not function well (though I blame the very cheap webcam because nicer webcams are less finicky). We fixed this by using a dedicated 2-amp battery for the Raspberry Pi.
- 2 rigid (non-swivel) casters with a wheel diameter of 32 mm
CodingKraken, https://github.com/CodingKraken, wrote an impressive modular scripting language for controlling a robot (unpublished by him), which I used to make the webserverScript folder! This currently-3-command language can be useful if the webcam has a huge delay or if you want to have fun trying to program obstacle courses! The scripting language is simple, and its documentation can be interactively used by typing the help command.
If your or another user's script is running, the Running box will be checked preventing new scripts from being run and preventing the "Reset GPIO settings" button from working. Updates on the progress of the script are sent to all users. It would be easy for you to change the Node.js code to have the "Reset GPIO settings" button always work, but then you should change the code so that pressing the button would remove all scheduled actions.
The code finds any improper syntax before starting to run the first line of your script. If improper syntax is found, the code will not run and the user (and not other users) will instead receive details on how to fix their script. This output of details will work even if another script is running, though it may get clobbered by the output from the script.
If you want to control a different servo motor or motors (or control the one I used differently), search for all instances of pinServo in all of the JavaScript files. If you want to control a different DC motor or motors (or control the one I used differently), search for all instances of pinMotor in all of the JavaScript files.
If you want to create a new command (such as pause or say), create its file in the commands folder. In the file, export config, run, and errorCheck. See existing command files for guidance. Your command's name, aliases, and any arguments should be lowercase because the .toLowerCase() method is used on the user's script.
You can test this code at Replit.com if you make a Node.js project. In webserver.js, set hardware to false, change port from 80 to 8080, set HTMLfolder and CommandsFolder to correct relative folder, and run node webserver.js in the Shell (no sudo).
To send audio, the Pi needs a USB microphone. Luckily, many USB webcams have built-in microphones!
Instead of sending the audio itself, I was hoping to do speech-to-text code. I tried AssemblyAI during April, 2023, but they no longer seem to have a free trial despite what their website says (when I try to connect my Pi, it tells me to pay them). However, I would rather not send a bunch of data over the Internet, so an offline approach might seem best. I installed SpeechCat (spchcat) on the Pi, but, as expected, it was extremely slow (there was a 30 second delay, which seemed to grow as it ran) on my Pi 3B and took up much computing power. SpeechCat is extremely easy to install and run (though getting it to install on my 64-bit OS required a few tricks), but I would need a much better processor with a good fan.
We can send audio directly over a network or over the Internet via VLC...
cvlc alsa://plughw:1 --sout '#transcode{vcodec=none,acodec=mp3,ab=128,channels=2,samplerate=44100}:std{access=http,mux=mp3,dst=:8087}'
For my microphone, after doing arecord -l and arecord -L and experimenting, I learned that plughw:CARD=C920,DEV=0 is what works for my specific microphone, though the plughw:1 in the above command works too! By the way, if plughw:1 isn't working for the USB speakers, you can do something similar for speakers using aplay -l and aplay -L. On Chrome (but not on Firefox and barely on Safari), viewing a webpage that contains
<audio controls>
<source src="http://<ip address>:8087" type="audio/mpeg">
</audio>
works okay as long as you play the audio immediately once the page starts or move the progress slider all the way to the right. Instead of this webpage, if you have VLC installed on your computer, to hear the audio, just open VLC then open network http://<IP address>:8087
Please let me know if you find a better solution!