7 steps to add multiple ToF LiDAR sensors to a micro:bit

By -
I'm happy with the solution I came up with to attach multiple Time-of-Flight (ToF) sensors to a Raspberry Pi or CircuitPython board.

Now I want to add one or more ToF sensors to Anastasia, my Python-powered micro:bit robot.

Anastasia needs at least one distance sensor to stop her running into things.

Since she can travel backwards as fast as she goes forwards, she really needs two sensors: one looking forwards, and one looking behind.

I've been looking for a simple solution but I have hit a snag.

I've found several Python drivers for the VL53L0X chip I'm using, but none will run on the micro:bit.

Some are Python wrappers for C code; others are just too big to fit on the micro:bit.

I finally came up with an approach which looks as if it may work.

The goal is to use a board with an Arduino-ish clone, programmed in C, driving the sensors and returning results via SPI.

Seven steps to ToF success


I've broken the project plan into seven steps which will build up into a complete solution.

  1. Arduino driving one sensor
  2. Arduino with more than one sensor
  3. Arduino(s) with one as SPI slave
  4. Arduino with more than one sensor that's interrupt-friendly
  5. Arduino with more than one sensor as SPI slave
  6. Arduino with level shifter and micro:bit
  7. 8MHz 3V3 Arduino and micro:bit
So far I've got, and run, sample code for the first three steps. The code so far has all come from reliable sources on the web. The core driver code and code for multiple sensors are Adafruit Arduino libraries for the VL53L0X. The SPI slave code comes from Nick Gammon's excellent site.

Step 4 needs a bit more thought. It's tempting to return floating-point values that show the measured distances, but there's a potential snag. The SPI save code is interrupt-driven, and I'd need to make sure that the code does not try to return a multi-byte value while that value is changing.

Concurrency rules


Rule one of concurrent programming is to avoid it if you can! Concurrent code is often hard to write, hard to read, and hard to test.

What I'll do is allow an SPI request that specifies which sensor to read. I'll return a single byte of data which will be a scaled distance measurement. If a valid distance can't be read I will return a value of zero.

I will be working on this over the next day or two and will report progress as I go.

Update


I forgot to mention that the code I'm using/developing is on GitHub.


Comments

Post a Comment

Popular posts from this blog

Controlling a Raspberry Pi Pico remotely using PySerial

By -
Image
Update : I'm using thie code below in another project, and found that I had not correctly fixed the reported bug. The new version passes automated tests, and I am pretty sure it works OK. I have changed the name of the class to Talker  since it can both send and receive information. Apologies to all concerned for the bug! Introduction You can use a Raspberry Pi Pico as a powerful peripheral to a host - a Raspberry Pi, a Jetson Nano, a laptop or workstation. In this article you'll see how to interact with a Pico running MicroPython or CircuitPython by writing some Python code that runs on the host. The software is easy to use. It enables you to send a Python statement to the Pico and read the results. The statement can be any valid MicroPython code. Setting up the host and the Pico For this article I've used a Raspberry Pi as the host, but any computer running Windows, Linux or Mac OS will do so long as it has Python 3.5 or later installed. In particular, you can use this t...
Read more

Five steps to connect Jetson Nano and Arduino

By -
Image
Yesterday's post showed how to link a micro:bit to the Jetson Nano. One of the members of the (unofficial) NVIDIA Jetson Nano group on Facebook asked about connecting an Arduino to the Jetson. Here's a simple recipe for getting data from the Arduino to the Jetson Nano. It should work on all the Jetson models, not just the Nano, but I only have Nanos to hand. On request, I've added a recipe at the end of this post which sends data from the Jetson Nano to the Arduino; it turns the default LED on the Arduino on or off. The recipe for sending data from the Arduino to the Jetson has just 5 stages: Program the Arduino. (I used the ASCIITable example). Connect the Arduino to the Jetson using a USB connector Install pyserial on the Jetson Download a three-line Python script Run the script.   Programming the Arduino I used an Arduino Uno, and checked it on a verteran Duemilanove (above), but any Arduino should work. You'll need to do this step usi...
Read more

Raspberry Pi Pico project 2 - MCP3008

By -
Image
This post show you how to drive the MCP3008 8-channel ADC using a Raspberry Pi Pico. I'll start with a personally embarrassing and annoyingly relevant story. I'll also tell you about a minor 'gotcha' when using SPI on the Pico, and how you can avoid it. Finally, I've include the code and fritzing diagram I used to test the interface. First, the story. Back in 2012, when the Raspberry Pi was fresh and new, I was running a startup called Quick2Wire.  We made add-on boards for the Pi. Just before Christmas we sent out our first batch of boards to a small army of beta-testers. The beta boards didn't work. Somehow a single trace on the pcb had got deleted and one of the GPIO pins was isolated. The boards were still usable and it wasn't too hard to solder in a jumper wire to replace the missing trace, but it was very embarrassing. It wasn't just that we'd shipped boards with a defect. The really annoying thing was that I'd set up an  automated loop-bac...
Read more