Does the WS2812 have integrated Gamma-Correction?

A while ago, I used transient current analysis to understand the behavior of the WS2812 a bit better (and to play around with my new oscilloscope). One intersting finding was that the translation of the 8 bit input value for the PWM register is mapped in a nonlinear way to the output duty cycle. This behavior is not documented in the data sheet or anywhere else. Reason enough to revisit this topic.

Measured PWM duty cycle vs. set value for WS2812S

Analyzing a Copper String Light with unusual Phosphor Converted LEDs

After being amazed about finding a really clever implementation of powerline controlled LEDs in a low cost RGB “copper string light”, I bought a few other products in hope to find more LEDs with integrated ICs. At less than $4.00 including shipping, this was by far the cheapest LED string I bought. This one did not have any ICs inside, but I was still surprised about finding rather unusual phosphor converted LED technology in it.

Controlling RGB LEDs With Only the Powerlines: Anatomy of a Christmas Light String

The RGB curtain predictably turns into a mess of wires when not used according to instructions.

As should be obvious from this blog, I am somewhat drawn to clever and minimalistic implementations of consumer electronics. Sometimes quite a bit of ingeniosity is going into making something “cheap”. The festive season is a boon to that, as we are bestowed with the latest innovation in animated RGB Christmas lights. I was obviously intrigued, when I learned from a comment on GitHub about a new type of RGB light chain that was controlled using only the power lines. I managed to score a similar product to analyze it.

The TransistorPixel

What would it take to build an addressable LED like the WS2812 (aka Neopixel) using only discrete transistors? Time for a small “1960 style logic meets modern application” technology fusion project.

Ultra Low Power LED Flasher using the Padauk PFS154

Flashing a LED is certainly among the first set of problems any burgeoning electronics specialist is tackling, may it be by using an ancient NE555 or, more recently, a microcontroller to control the LED. As it turns out, we can turn any trivial problem into a harder one by changing its constraints.

Power Analysis: Probing WS2812 RGB LEDs

Power analysis is a technique to probe the inner workings of an integrated circuit by measuring changes in the supply current. Whenever a logic gate switches, it will cause a tiny current spike that can be measured externally. By inspecting the temporal variation, especially in reaction to an external signal, it is often possible to deduce information about the construction of the IC.

A few years ago I used a logic analyzer to investigate the protocol of the, then new, WS2812 RGB LED. So, why not revisit this topic to test my newly acquired deep sampling oscilloscope?

Building a Chaotic Oscillator from Common Components

Sometimes you find things you have not even been looking for…

A chaotic oscillator is an electronic circuit that can exhibit “chaotic“, nonperiodic behavior. A commonly cited example is Chua’s circuit, but there are many others. I always regarded these as carefully designed, rather academic, examples. So I was a bit surprised to observe apparently chaotic behavior in a completely unrelated experiment.

Intelligent 7-Segment Display

Time for another project with a super-low-cost microcontroller. But what to design? Ever since seeing a project where a $0.03 MCU controls $40 worth of intelligent RGB LEDs, I have been wondering whether this is the right place to use these devices. At this price point, doesn’t it seem to make more sense to dedicate one MCU to one LED each and use it to implement a fancy node-controller? It has always appealed to me to design my own protocol. However, just copying a WS2812 RGB LED or similar seemed to be a bit pointless…

What made the 1960s CDC6600 supercomputer fast?

Anybody who has ever taken an advanced computer architecture class has heard of the CDC6600, which was the world’s fastest computer from 1964 to 1969. It was the machine that put Seymour Cray on the map as a supercomputer architect. The design of the machine is well documented in a book by James Thornton, the lead designer, and is therefore publically accessible. Among several architectural concepts that later found use in RISC, the CDC6600 is known for introducing the Scoreboard. Which is, along with Tomasulo’s algorithm, one of the earliest concepts for out-of-order processing.

Besides the architectural progress, the CDC6600 was impressive for its clock speed of 10 MHz. This may not sound much, but consider that this was a physically very large machine entirely built from discrete resistors and transistors in the early 1960s. Not a single integrated circuit was involved. For comparison, the PDP-8, released in 1965 and also based on discrete logic, had a clock speed of 1.5 MHz. The first IBM PC, released 20 years later, was clocked at less than half the speed of the CDC6600 despite being based on integrated circuits. The high clockrate is even more impressive when comparing it to more recent (hobbyist) attempts to design CPUs with discrete components such as the MT15, the Megaprocessor or the Monster6502. Although these are comparatively small designs based on modern components, none of them get to even a tenth of the CDC6600 clock speed.

A LED-Candle based on the 3 cent MCU

After having reviewed sub $0.10 microcontrollers recently, it’s time for some projects using the Padauk PFS154 and PMS150C. Considering my previous investigation of electronic and non-electronic candles, it appears only natural to chose this as a target for the lowest cost microcontrollers.