paul's blog

Better SPI Bus Design in 3 Steps

Most Arduino SPI tutorials show this simple but poor SPI bus design:

A much better SPI bus design can prevent conflicts.  3 simple improvements are needed:

  1. Use pullup resistors on all chip select signals.

  2. Verify tri-state behavior on MISO: use a tri-state buffer chip if necessary.

  3. Protect bus access with SPI.beginTransaction(settings) and SPI.endTransaction().

Click "Read more" for details on these 3 steps.

Making nRF8001 (Bluetooth LE) and SD cards play nice together

Been working on making Adafruit_nRF8001 and the SD library work together.  Details are on this forum thread, and also this one.

Windows 10 Preview Build 9860 *finally* fixes USB Serial

I am happy to report Windows 10 Preview build 9860 fixes the long-standing USB serial bugs, which impact nearly all Arduino compatible boards.

  • The driver loads automatically.  No 3rd party INF is required.
  • The surprise removal bug is finally fixed (was present in build 9841, is fixed in 9860)
  • The seconds-long pause when detecting a new USB device for the very first time appears to be gone.

Windows 10 is finally going to support all class-compliant USB serial (eg, CDC-ACM) as well as Linux and Mac OS-X.  Very exciting.

Embrace Heart Lighting

Earlier this summer, I worked on a tiny piece of the Embrace sculpture, for Burning Man 2014.

Inside were 2 hearts, one made here in Portland by Lostmachine Andy & other burners at Flat Rat Studios.  I made electronics to gradually fade 4 incandescent light bulbs in heart beating patterns.

Click "Read more" for technical details and many more wonderful photos (taken by Sarah Taylor)....

Node-RED Hacking - Audio Library Front-End

When I started the Audio library, a nice GUI (like Puredata or Max/MSP) seemed an impossibly distant dream.  Then, in this forum thread, I learned of the open source Node-RED project.

Over the last few days I've been coming up to speed on modern Javascript tools like jQuery and D3, to hack Node-RED into a GUI front-end.  Much work still needs to be done before this is usable, but I'm pretty excited about the possibilities!

Update: a live demo page is now available.  :)

Display & SPI Optimization

Recently I've been working on an optimized ILI9341 display library, to take advantage of Teensy 3.1's more capable SPI hardware.  Here's a quick video demo, so you can see how much of a difference it makes.

In the transition from 8 to 32 bit microcontrollers, on-chip SPI ports usually gain more sophisticated features.  Special programming is needed to fully levergage these more powerful features.  Merely recompiling code designed for simple SPI hardware on 8 bit hardware rarely acheives the best performance.  As you can see in the video, optimizing for these features makes a pretty dramatic improvement.

Click "Read more" for the all the technical details...

SPI Transactions in Arduino

For the last several weeks, I've been working on SPI transactions for Arduino's SPI library, to solve conflicts that sometimes occur between multiple SPI devices when using SPI from interrupts and/or different SPI settings.

To explain, a picture is worth 1000 words.  In this screenshot, loop() repetitively sends 2 bytes, where green is its chip select and red is the SPI clock.  Blue is the interrupt signal (rising edge) from a wireless module.  In this test, the interrupt happens at just the worst moment, during the first byte while loop() is using the SPI bus!

Click "Read mode" for lots more detail.....

RFM69 Wireless & SPI Bus Sharing (feedback wanted...)

Recently I've been working to improve the Arduino SPI library, to better support multiple SPI devices with different settings, and SPI devices requiring interrupts.

Today I discovered a new problem while testing the HopeRF RFM69 wireless module.

Click "Read more" for details and the workaround I found....

Large LCD Reverse Engineering

Years ago, around the time DorkbotPDX's meetup moved from Vendetta to NW Lucky Lab, Ben Bleything brought LCDs from decommissioned point-of-sale terminals to the meetup.  I did some reverse engineering to get them working!

At the time, I wrote 3 blog articles aboug the reverse engineering effort.  Only one of them survived from the early days of this website.  Recently, I found the original text those old 3 articles, and also a small pile of the LCDs... which I'll be giving away at upcoming meetings!

Click "Read more" for those 3 original articles with the fine details of reverse engineering (and source code) for these old LCDs....

Maker Faire 2014

Maker Faire went really well.  I had a booth about the new audio library, and we also built a OctoWS2811 LED display for Freescale's booth.

Click "Read more" for more photos...

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