Matthew Petroff https://mpetroff.net mpetroff.net Sat, 31 Mar 2018 01:36:29 +0000 en-US hourly 1 Color Cycle Picker https://mpetroff.net/2018/03/color-cycle-picker/ https://mpetroff.net/2018/03/color-cycle-picker/#respond Sat, 31 Mar 2018 01:36:29 +0000 https://mpetroff.net/?p=2610 Continue reading ]]> The “category10” color palette, originally developed by Tableau, was adopted as the default color cycle for Matplotlib 2.0 and is also used by default by D3.js and Vega, along with other software packages. While more aesthetically pleasing than the old Matplotlib default, it is unfortunately not colorblind-friendly.1 In an effort to improve this and promote the development of colorblind-friendly color cycles for scientific visualization, I built a color cycle picker that incorporates color vision deficiency simulation and enforces a minimum perceptual distance between colors, for both normal and anomalous trichromats. This is accomplished by performing color vision deficiency simulations2 for various types of deficiencies and enforcing a minimum perceptual difference for the simulated colors using the CAM02-UCS3 perceptually uniform color space (each type of deficiency is treated separately). Additionally, a minimum lightness distance is enforced, for better grayscale printability. The tool allows colors to be picked from a visualization of the CAM02-UCS color gamut and assembled into a color cycle. This visualization is performed using hardware-accelerated WebGL to allow for real-time interactive adjustment of parameters; the resulting palette is also visualized. The minimum perceptual color distance, lightness distance, and color vision deficiency simulation parameters are all adjustable. A hosted copy is provided, and the code is available in a repository on GitHub.

Color Cycle Picker Screenshot


  1. Personally, I have difficulty telling the second and third colors apart.  

  2. G. M. Machado, M. M. Oliveira and L. A. F. Fernandes, “A Physiologically-based Model for Simulation of Color Vision Deficiency,” in IEEE Transactions on Visualization and Computer Graphics, vol. 15, no. 6, pp. 1291-1298, Nov.-Dec. 2009. doi:10.1109/TVCG.2009.113  

  3. Luo M.R., Li C. (2013) CIECAM02 and Its Recent Developments. In: Fernandez-Maloigne C. (eds) Advanced Color Image Processing and Analysis. Springer, New York, NY. doi:10.1007/978-1-4419-6190-7_2  

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Pannellum 2.4 https://mpetroff.net/2018/01/pannellum-2-4/ https://mpetroff.net/2018/01/pannellum-2-4/#comments Wed, 31 Jan 2018 21:14:03 +0000 https://mpetroff.net/?p=2597 Continue reading ]]> Yesterday, I released Pannellum 2.4.0. It doesn’t contain any major new features, although it does finally include translation support, which was an often requested feature. Also included are numerous minor improvements, a few new API functions, and quite a few bug fixes; see the changelog for full details. It had been more than a year since the last release—and I’ve been meaning to create a new release for a few months—so it was high time for a new release.

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Amazon Echo Button Teardown https://mpetroff.net/2017/12/amazon-echo-button-teardown/ https://mpetroff.net/2017/12/amazon-echo-button-teardown/#comments Sun, 31 Dec 2017 21:18:50 +0000 https://mpetroff.net/?p=2561 Continue reading ]]> Amazon recently released the Echo Button, a Bluetooth Low Energy device designed for use with Echo devices (which I don’t own). Although it uses Bluetooth instead of Wi-Fi, I thought it might be a better device to repurpose than the Dash Button, due to its larger size and easily replaceable battery. Thus, I bought one to take apart.

Echo Button outside

Amazon seemed really worried about the batteries falling out, since the battery door is held shut with both a plastic tab and one Phillips #1 screw. Underneath one of the two AAA batteries is a row of exposed test points. Four other Phillips #1 screws are hidden beneath the device’s rubber feet; removing these allows the device to be opened.1

With battery door open

Once opened, there are two parts—a top half with the large button, and a bottom half with the PCB and batteries.

Halves separated

The top half consists of three plastic parts, three button contacts, and four springs.

Top half parts

The bottom half consists of one plastic piece, with the battery compartment, and the PCB, secured with two more Phillips screws.

Bottom half parts

The device can be easily disassembled and reassembled with standard tools and without damaging it.

All parts

The PCB is fairly spartan, consisting of a combined microcontroller / Bluetooth Low Energy SoC, three RGB LEDs,2 a trace antenna, and supporting components. For easy hackability, there’s a Tag-Connect SWD footprint, as well as a U.FL antenna connector and numerous cuttable traces / solder jumpers. The SoC is a Cypress CYW20735 “single-chip Bluetooth transceiver for wireless input devices.” There appear to be freely available development tools for it.

PCB top

The bottom of the PCB includes a set of test points, some of which are accessible from within the battery compartment. In particular, the SWD header is accessible via these test points with the following mapping:

 TMF2: SWDIO
 TMF9: SWCLK
TMF10: GND
TMF11: RESET
TMF12: VCC
TMF22: SWO

PCB bottom

As far as software goes, the device broadcasts as a Bluetooth Low Energy gamepad with ID EchoBtn2V8.3 I was able to successfully pair it to a computer, but I have not yet tried to use it as an input device. I have also not yet tried to connect a debugger to the SoC.


  1. There’s no glue or ultrasonic welding. 

  2. There’s also a fourth, unpopulated footprint. 

  3. The last three characters might be specific to my device. 

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Light Bulb PCB https://mpetroff.net/2017/11/light-bulb-pcb/ https://mpetroff.net/2017/11/light-bulb-pcb/#respond Sun, 05 Nov 2017 18:45:39 +0000 https://mpetroff.net/?p=2538 Continue reading ]]> As part of a Halloween costume (I was a “bright idea”), I designed a light bulb PCB, which was mostly just an excuse to try out PCBmodE. It consists of seven addressable RGB LEDs, an ATtiny85 microcontroller, an ambient light sensor, and a rechargeable battery. The battery and an old hard drive magnet, for mounting the PCB, are attached to the back via double-sided tape. As one might expect, PCBmodeE worked well for this artistic circuit board design, given that it was designed to be used for something like this, but KiCad is much easier to use for just about everything else.

Light Bulb PCB: Front

Light Bulb PCB: Back

The ambient light sensor proved less useful than I had hoped—the LEDs were too bright to use with all but their dimmest settings, and the light sensor’s optimal range didn’t align well with the lightning levels I was interested in. I also should have placed a copper pour behind the soldermask for the majority of the bulb, since it would have made for a better yellow color. Finally, the footprint I made for the microcontroller footprint is too narrow, but it’s close enough that I was still able to solder the microcontroller in place; a slightly wider footprint for the ambient light sensor would have also made soldering easier. Since this was a one-off, and it’s now past Halloween, there’s no reason for me to revise the PCB to fix these shortcomings.

The design files are in a GitHub repository.

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Reserva Nacional Los Flamencos https://mpetroff.net/2017/10/reserva-nacional-los-flamencos/ https://mpetroff.net/2017/10/reserva-nacional-los-flamencos/#respond Tue, 31 Oct 2017 22:44:26 +0000 https://mpetroff.net/?p=2523 Continue reading ]]> While recently in San Pedro de Atacama, Chile, I drove out towards Argentina to look at the national flamingo reserve, which consists of a number of salt lakes (with flamingos). There are also other interesting geologic formations including rocks sticking out of the desert, the “Monjes de la Pacana.” Here are some photos of the reserve.Laguna Aguas Calientes

Monjes de la Pacana

Monjes de la Pacana

Laguna Aguas Calientes

Monjes de la Pacana

Monjes de la Pacana

Monjes de la Pacana

Laguna de Pujsa

Andean Gulls

Laguna de Pujsa

Flamingos at Laguna de Pujsa

Laguna de Pujsa

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