MicroPlot on the PyPortal - progress and frustration

By -

Update: I got a fix within minutes of posing the problem on the Adafruit discord channel!

Here's the correct bitmap:

The problem is now solved,

MicroPlot now runs well on the Adafruit PyPortal and  Clue as well as the Pimoroni Pico Explorer base, but I've been tearing my hair out trying to solve a problem saving bitmaps.

The bitmap problem

Here's a screenshot of a display on the PyPortal together with the bitmap file which should show what's on the screen. I could not work out what's going wrong.

The code creates the plot and then uses the screenshot code that Adafruit provides.

import math
from plotter import Plotter
from plots import LinePlot
import board
import digitalio
import busio
import adafruit_sdcard
import storage
from adafruit_bitmapsaver import save_pixels


def plot():
    sines = list(math.sin(math.radians(x))
                 for x in range(0, 361, 4))
    lineplot = LinePlot([sines],'MicroPlot line')
    plotter = Plotter()
    lineplot.plot(plotter)


def save():
    spi = busio.SPI(board.SCK, MOSI=board.MOSI, MISO=board.MISO)
    cs = digitalio.DigitalInOut(board.SD_CS)
    sdcard = adafruit_sdcard.SDCard(spi, cs)
    vfs = storage.VfsFat(sdcard)
    storage.mount(vfs, "/sd")
    save_pixels("/sd/screenshot.bmp")


plot()
save()
print('done')

What works, what doesn't?

When I first wrote about MicroPlot it ran on the Pico. The code worked but I knew it would need refactoring as I extended it to cover other plot types and other devices.

Past experience has taught me the value of automated tests for embedded projects. I wondered if I could capture MicroPlot's output in bitmap files and use them in tests. I didn't know much about the format of Bitmap files so I started to look for code I could borrow and adapt.

I soon discovered that bitmap files could use different ways of encoding colour, and the simplest, smallest format created monochrome bitmaps.  I soon got a Bitmap file-saver working reliably on the Pico. As you can see, it works, and you can find the code in the MicroPlot project on GitHub.

Soon after that I discovered some Adafruit colour bitmap saver code and adapted it to run on the Pico. As you can see, it too worked well.

But...

When I ran the unmodified Adafruit code on the PyPortal, it scrambled the image, as shown earlier.

I've checked that I am using the latest production versions of the Adafruit code. Can anyone suggest what I'm doing wrong? The code (mine and Adafruit's) looks sensible, but it seems to corrupt every screenshot  bitmap that I try to take.

If you can spot the problem, let me know in the comments, tweet to @rareblog or respond to my cry for help on Discord.





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