µ-Wire – USB on an ATtiny 10

Atmels AVR ATtiny10 are surprisingly powerful devices that come in an extremely tiny SOT23 package with only 6 pins. The have 1kb of flash, 32 bytes of SRAM and use the reduced AVR core which only supports 16 instead of 32 register. It seems like Atmels idea of these devices is to use them as an advanced blinker, and to replace tiny logic circuits. But other people have shown that much more is possible. For example the noiseplug (video), a chiptune player, and a Simon Says game.

I previously used the ATtiny10 in the TinyTouchbutton, a touchbutton controlled light with WS2812 LEDs. This time I aimed higher: Is it possible to turn the ATtiny10 into a USB compatible device? My goal was to implement a subset of the little-wire functionality to control a WS2812 LED by USB. This takes 3 I/O lines, which is exactly the number of free pins on the ATtiny10.

Littlewire supports several functions to control WS2812 LEDs on arbitrary I/O ports. I simplified this to only supporting a single LED on a specific pin, however still retained protocol compatibility. This means that all the little-wire host-programs still work. The finished device can, for example, be used as an RGB indicator LED similar to the Blink(1).

My test setup is shown below. The ATtiny10 is almost the smallest part of the circuit. There are some discrete components on the rear-side of all PCBs, so do not be surprised about missing decoupling capacitors, zener diodes and resistors.

u-wire-test Continue reading “µ-Wire – USB on an ATtiny 10”

Interrupt free V-USB

Starting with V2.0, Micronucleus is going to use an interrupt free modification of the software USB implementation V-USB. This provides significant benefits for the bootloader, as it is not necessary anymore to patch the interrupt vector of the user program. A surprising side effect was a speed up of the V-USB data transmission,  which may also be helpful in other applications. Here, I try to give a rough overview about the meandering work that led to this achievement.

Previous versions of Micronucleus (and also the Trinket bootloader) use an ingenious mechanism devised by Louis of embedded creations to patch the interrupt vector transparently to the user program. Although this approach works very well, it still adds a lot of complexity to the bootloader, will add a couple of cycles of interrupt delay, and carries the risk of breaking the user program in a few rare cases. Removing this burden allows for a drastic reduction in code size and improved robustness. Continue reading “Interrupt free V-USB”

Follow up on Candle Flicker LEDs

I previously reported on reverse engineering a candle flicker LED. My approach was to extract the “flicker” pattern from the input current variation and to deduce the algorithm from statistical analysis.

Reverse engineering the controller chip

Of course there is another, more involved, approach. And that is to reverse engineer the circuit directly from the die. Andrew Zonenberg from Siliconpr0n decapsulated and imaged the controller chip from one of my LEDs. You can find his report here.

He managed to obtain very high-resolution optical microscopy images of the top-level metal. It turns out that the controller chip is manufactured in a relatively coarse CMOS process with one metal layer and 1-2 µm resolution. This is 1980ies technology. But of course, that is all that is needed for a circuit as simple as a flicker-LED.

candle_bf_neo40x_small Continue reading “Follow up on Candle Flicker LEDs”

Light_WS2812 library V2.0 – Part I: Understanding the WS2812

WS2812 LEDs are amazing devices – they combine a programmable constant current controller chip with a RGB LED in a single package.  Each LED has one data input and one data output pin. By connecting the data output pin to the data input pin of the next device, it is possible to daisy chain the LEDs to theoretically arbitrary length.

Unfortunately, the single-line serial protocol is not supported by standard microcontroller periphery. It has to be emulated by re-purposing suitable hardware or by software timed I/O toggling, also known as bit-banging. Bit-banging is the preferred approach on 8 bit microcontrollers. However,  this is especially challenging with low clock rates due to the relatively high data rate of the protocol. In addition, there are many different revisions of data sheets with conflicting information about the protocol timing. My contribution to this was the light_ws2812 library V1.0 for AVR and Cortex-M0, which was published a while ago. A V2.0 rewrite of the lib was in order due to various reasons. And, to do it right, I decided to reverse engineer and understand the WS2812 LED protocol to make sure the lib works on all devices.

ws2812_compared Continue reading “Light_WS2812 library V2.0 – Part I: Understanding the WS2812”

Breadboardable break-out board for the NXP LPC812

The NXP LPC800 series is an interesting entry in the Cortex M0+ microcontroller market, aiming to replace 8 bit microcontrollers at the low end. The largest member of the family, the LPC812 is a device with 16kb flash and 4kb SRAM. It is available in a TSSOP20 package which is really small, but still easily solderable. Since I prefer to work with microcontrollers with as little added clutter as possible, I designed a small break-out board for this device.

The board includes push buttons for reset and activating the serial bootloader. It has an integrated 500mA 3.3V LDO to supply both the MCU and connected devices from the USB port. The four pins on the top side (5V,RX,TX,GND) can be used to connect a cheap USB to serial adapter (<$2 on ebay) and program the device via the internal bootloader using FlashMagic.

The entire board with LPC812 is smaller than a DIP LPC1114. Due to it’s narrow design, it is even useful on very small 170 pin bread-boards.

The Github repository has all design data.

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