RVR Programming
In order to operate the RVR in both manual and auto modes, we will have to write two programs - one that runs on our phones and one that runs on the micro:bit itself. Using our phones, we will be able to manually drive the RVR for certain parts of the competition. For other parts we will need the RVR to drive itself. For this, we'll program the micro:bit to control the RVR.
If you've completed the RVR assembly, you probably noticed that we installed a remote trigger at the rear of the RVR. We will use that trigger to switch between manual and auto modes. By turning on the IR transmitter on the back of the RVR (using a program on our phone), the remote trigger will sense the IR light and signal the micro:bit to run its obstacle avoidance algorithm. When we turn off the IR transmitter (again, using the program on your phone), the micro:bit will stop executing the obstacle avoidance algorithm.
Sphero EDU App
In order to manually drive the RVR (and the Sphero mini's), you will need to download and install the Sphero EDU app. It's available at the following links for iPhone/iPad and Android, respectively.
Apple app store link: https://apps.apple.com/us/app/sphero-edu/id1017847674
Google Play link: https://play.google.com/store/apps/details?id=com.sphero.sprk
The app is fairly straightforward. Once you've downloaded it, you'll need to create an account. After signing in, you can manually drive the robots, or you can write programs to automate their actions. That's what we'll do. Our program is very simple, though. All we need to do is turn on or off the IR transmitter on the back of the RVR. The Sphero app uses block coding to write these programs. Below is a screen shot of the program you should create.
As you can see, it's a very simple program. When you press "start", the RVR begins emitting IR light out of the IR transmitter mounted on the rear of the RVR. The littleBit i7 remote trigger detects that light and signals the micro:bit to start its obstacle avoidance algorithm. The RVR will continue to run this algorithm until you press "Stop".
micro:bit Program
This is where the real magic happens. This program will enable the RVR to drive itself, while (hopefully) avoid crashing into obstacles (walls). In the most simple terms, whenever the RVR is emitting IR light (controlled by the program running on our phone) the micro:bit will execute the obstacle avoidance. The program that we'll write will tell the RVR to drive forward while monitoring the proximity sensors. If both sensors are detecting an obstacle, the RVR will turn left. If only one sensor is detecting an obstacle, the RVR will turn the direction opposite of that sensor (i.e. if the left-hand sensor detects an obstacle, the RVR will turn right and vice versa) . When the IR light is turned off (the program running in the Sphero EDU app on your phone is "stopped"), the micro:bit will stop running the obstacle avoidance algorithm.
Here's the block code of the program:
This program is available here. Simply download the .hex file, then plug the micro:bit into your computer and copy/paste the .hex file onto the micro:bit. It will automatically install.
The current version of the micro:bit code, as of 9/13/21, is REV A.
Improve the RVR Performance (optional)
The basic obstacle avoidance program is provided for you above, but if you want to boost the performance of the RVR, you can recreate the program and tweak the values yourself!
In order to create the program shown above, you will need to navigate to the Microsoft MakeCode website: https://makecode.microbit.org/. and click "New Project". Now that you have a new project open, you need to add an extension specific to the Sphero RVR. To do so, click "Advanced" in the tray, then click "Extensions". The extension isn't listed by default, but it's easy to find. Simply copy and paste this URL into the search bar and hit search: https://github.com/sphero-inc/sphero-sdk-microbit-makecode.git. Then click on the "SpheroRVR" search result. The extension will be automatically downloaded and installed for you.
Now you can click and drag the appropriate blocks to build the wall following algorithm. Once you have an algorithm you'd like to test, simply save the .hex file, plug in the micro:bit to the computer, and click and drag the .hex file onto the micro:bit. It will automatically install.
Some tips for building your own program:
The "heading" and "count" variable were created under the Variables tab
Make sure the analog pins you select correspond to how the sensors are plugged in to the micro:bit. If you followed the build tutorial correctly, the analog pins are correctly called out in the block code shown above.
Try changing the proximity sensor sensitivity and the speed to see if you can make your RVR the fastest and most reliable!
If you have questions you can always reach out to us through the Microsoft Teams VRC Portal.
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