One of the tricky things about making transitions through the canvas is finding cable parts that make right-angle type turns on each side. The ribbon cable system I showed in the last section may be the best set of parts Adafruit currently offers for these right-angle USB cable turns.

But another way of making right (or left, or up, or down) cable turns is to find (or fabricate) a custom cable with the desired length and orientation.

This picture shows a whole bunch of USB cables I have collected that have various styles of right/left/up/down turns.

You can find these at sites like Amazon by searching for "short left right angle micro USB cable" or similar. These often come in pairs with both the "left" and "right" versions. I look for the pairs because it's sometimes hard to figure out which of the two I will need until I have them in hand.

I am going to use one of the "angled USB adapters" shown here - whichever one happens to angle the way I want.

In addition to one of the USB adapters shown above, I will use the following Adafruit parts. You may already have some of these from the earlier experiments in interior lighting. If so, you can repurpose them here as I did.

1 x Adafruit GEMMA M0
Gemma M0 with DotStar RGB LED
1 x USB cable - 6" A/MicroB
USB cable for Gemma M0
1 x Snap-In Panel Mount Cable - USB A Extension Cable
another of the USB panel mount cables

These pictures shows the parts described above. As with the CPX, I tested the full cable assembly for the Gemma M0 before committing any of it to the canvas.

Here I measured and then cut another 1.1 by 1.9 cm hole in the canvas. I'm placing this one a little lower than the other. As before, I've checked both side of the canvas to make sure the cable will not bump into anything on the inside.

These pictures show how I've snapped the panel mount USB cable into the canvas - after making sure the orientation of the cable works with the USB adapter I chose.

Then I connected the cable assembly with the Gemma M0. This is another situation where I needed to do a lot of "cable massage" to get the short USB cable into the curly shape you can see here.

I think one set of the nylon screw parts will be enough to keep the Gemma M0 attached to the canvas. These pictures show how I marked a spot on the canvas to attach the Gemma M0 through the hole near the 'A' in 'GEMMA' on the silk screen.

Now we can try out lighting tests with the DotStar RGB LED on the Gemma M0.  See this Gemma M0 guide page for all the details. You may need to first copy the adafruit_dotstar library to your Gemma M0. With that library you should be able to see some color from the DotStar in the CircuitPython REPL with commands like this:

import adafruit_dotstar
led = adafruit_dotstar.DotStar(board.APA102_SCK, board.APA102_MOSI, 1)
led[0] = (80, 0, 80)

Here I will once more attach the NeoTrellis M4 to the Raspberry Pi using the nylon screw set. The first picture shows both USB cables, but I will only use the longer cable for this.

I want the NeoTrellis M4 to sit vertically, behind the rPi and the USB cables sprouting out of it. Note that I am connecting to a different corner of the rPi than in previous instances where I mounted the NeoTrellis M4.

I threaded the USB cable for the NeoTrellis M4 through the USB speaker cable and then arranged it so the extra cabling rests on the bottom of the canvas frame, as shown here.

This picture shows what it looks like when you boot a Raspberry Pi with 3 CircuitPython devices attached.

Note how we can print out the boot_out.txt files to see which of the CIRCUITPY directories corresponds to which device.

Also note how we have the 3 ttyACM devices in /dev. I don't know how to tell which is which other than using screen to connect to the REPL of each one.

Here I am conducting light tests with all three CircuitPython devices.

I am now going to declare this CompuCanvas finished from a hardware point of view. The Python light show code could be tweaked endlessly, but I will leave that as an exercise to the reader.

Here are several more pictures with different lighting configurations.

Now with the physical construction of this CompuCanvas finished, we are almost at the end of this guide.

But there is one loose end to return to: the configuration of the USB speaker. The next (and final) section will detail how to test and configure the USB audio.

This guide was first published on Dec 11, 2019. It was last updated on Dec 11, 2019.
This page (More External Features) was last updated on Dec 24, 2019.