Hardware Hacking & Web-Technology

Slides from my talk at #jsunconf in Hamburg.

1. Martin Schuhfuss – @usefulthink something with raspberry-pi, hardware-hacking and hardware-hacking & web-technology
2. rpi-ws281x Martin Schuhfuss – @usefulthink
3. ws2812 LED-Controller ws2811 rpi- full-color LED with integrated controller
4. (image from http://www.adafruit.com/products/1138)
5. how it works
6. ws2812 how LEDs are connected LED 01 DIN DOUT LED 02 DIN DOUT LED 03 DIN DOUT +5V GND +5V GND +5V GND +5V GND DATA
7. ws2812 how colors are sent to the LEDs LED 01 DIN DOUT Register #000000 LED 02 DIN DOUT Register #000000 LED 03 DIN DOUT Register #000000 +5V GND +5V GND +5V GND DATA +5V GND
8. ws2812 how colors are sent to the LEDs LED 01 DIN DOUT Register #ff8800 #ff8800 1 LED 02 DIN DOUT Register #000000 LED 03 DIN DOUT Register #000000 — — +5V GND +5V GND +5V GND DATA +5V GND
9. ws2812 how colors are sent to the LEDs LED 01 DIN DOUT Register #ff8800 LED 02 DIN DOUT Register #000000 LED 03 DIN DOUT Register #000000 — +5V GND +5V GND +5V GND DATA +5V GND
10. ws2812 how colors are sent to the LEDs LED 01 DIN DOUT Register #ff8800 #00ffff 2 LED 02 DIN DOUT Register #00ffff LED 03 DIN DOUT Register #000000 #00ffff — +5V GND +5V GND +5V GND DATA +5V GND
11. ws2812 how colors are sent to the LEDs LED 01 DIN DOUT Register #ff8800 LED 02 DIN DOUT Register #00ffff LED 03 DIN DOUT Register #000000 +5V GND +5V GND +5V GND DATA +5V GND
12. ws2812 how colors are sent to the LEDs LED 01 DIN DOUT Register #ff8800 #0000ff 3 LED 02 DIN DOUT Register #00ffff LED 03 DIN DOUT Register #0000ff #0000ff #0000ff +5V GND +5V GND +5V GND DATA +5V GND
13. ws2812 how colors are sent to the LEDs LED 01 DIN DOUT Register #000000 reset 4 LED 02 DIN DOUT Register #000000 LED 03 DIN DOUT Register #000000 reset reset +5V GND +5V GND +5V GND DATA +5V GND
14. more detail… (image from http://sklep.atnel.pl/pl/p/WS2812B-TASMA-RGB-W-0,5m/98)
15. ws2812 HARDWARE ‣ SMD5050 Package ‣ ws2811 controller ‣ three LEDs
16. colors on the wire one-wire serial data-signal 1 0 1 1 0 0 1 0 1 0 0 0 0 0 0 0 1 1 1 1 0 1 0 0 8 0 2 b f 4 #80b2f4 in HTML-Notation duration: 30µs (33k color-values per second)
17. (image from http://www.electrobob.com/ws2812-level-translator/) this is what bits really look like. (scale: t = 0.5µs, U = 1V)
18. 3.75µ s 1.25µ s 0V +5V t wavelength λ pulsewidth frequency 800kHz wavelength 1.25µs 0 2.5µ s 5µ s 1 0 1 1 PWM-Signals transport binary data with just one wire
19. PWM-Signals transport binary data with just one wire 0V +5V λ = 1.25µs (±600ns) (f = 800kHz) 350ns (±150ns) 800ns (±150ns) 0 t
20. 0V +5V λ = 1.25µs (±600ns) (f = 800kHz) 750ns (±150ns) 600ns (±150ns) 1 t PWM-Signals transport binary data with just one wire
21. drivers
22. (image from http://www.electrobob.com/ws2812-level-translator/) the signal-level needs to be changed 1.6 Million times per second. problem
23. Arduino: no problem* ‣ CPU running at 16MHz ‣ 62 nanoseconds per instruction ‣ quite some time in between level changes (20 instructions per bit)… ‣ nothing else running on the CPU * requires assembler-programming to get this right :/
24. Arduino: but… ‣ no higher-level languages 
 (actually, just C and ASM) ‣ integration with stuff™ hardly possible ‣ booooring!
25. Raspberry Pi ‣ Broadcom BCM2xxx SoC ‣ 700MHz ARM CPU / 512MB RAM ‣ SD-Card as Harddrive ‣ 100MBit LAN / HDMI / USB / Audio ‣ runs raspbian OS ‣ …and is really cheap Ethernet HDMI micro-USB (power supply) SD-Card GPIO Status-LEDs USB Digital-Audio Analog-Audio
26. Raspberry Pi ‣ interface to external hardware ‣ controllable logic-pins ‣ sensors, motors, anything ‣ SPI / UART / I2C GPIO
27. Raspbian: problem ‣ because multitasking ‣ nearly impossible to get the timing right ‣ when processes run depends on lots of factors we can’t really control
28. Raspberry Pi PWM ‣ „serializer“-mode ‣ bits in data-registers represent signal-level per PWM-cycle ‣ only a few bytes in registers ‣ needs DMA to transport data
29. Raspberry Pi PWM 0V +5V PWM cycle: 416ns (frequency: 2.4 MHz) 0 t 1 0 0 bits written to PWM-Registers
30. Raspberry Pi PWM 0V +5V PWM cycle: 416ns (frequency: 2.4 MHz) 1 t 1 1 0 bits written to PWM-Registers
31. Raspbian: problem ‣ store prepared pixel-data in memory ‣ let the DMA-Controller transfer data to PWM-Module ‣ CPU or OS are not involved!
32. how it works…
33. lets just say it's complicated.
34. ‣ awesome C-Library by Jeremy Garff ‣ base for everything that follows rpi_ws281x // configuration and central data-structure ws2811_t ledstring = { .freq = TARGET_FREQ, .dmanum = DMA, .channel = { [0] = { .gpionum = GPIO_PIN, .count = NUM_LEDS, .invert = 0, .brightness = 255 }, [1] = { … } }, }; // setup all that complicated hardware-stuff ws2811_init(&ledstring); // write some RGB-values to the LED-array ws2811_led_t* leds = ledstring.channel[0].leds; leds[42] = 0xff0000; leds[23] = 0x0000ff; // send it away ws2811_render(&ledstring); // …sometime later: tear-down complicated stuff ws2811_fini(&ledstring);
35. let's do this in Javascript
36. ‣ native node.js-bindings for rpi_ws281x ‣ JS-interface mirrors the C-API ‣ wrapper handles only type-checking and conversions between V8-types and C rpi-ws281x-native var ws281x = { init: function(numLeds, options) { … }, /** @param {Uint32Array} ledData */ render: function(ledData) { … }, reset: function() { … } }; npm install
37. hello rainbow var ws281x = require('rpi-ws281x-native'),
 pixelData = new Uint32Array(100);
 
 ws281x.init(100);
 
 // ---- animation-loop
 var offset = 0;
 setInterval(function () {
 for (var i = 0; i < 100; i++) {
 pixelData[i] = rainbowColor((offset + i) % 256);
 }
 
 offset = (offset + 1) % 256;
 ws281x.render(pixelData);
 }, 30);

38. ‣ API is a bit too low-level ‣ need to manually manage the data-array ‣ numbers as colors are complicated ‣ no shapes, nothing useful. problems hello rainbow
39. hello web-technology ‣ want to draw lines, shapes, text, … ‣ need fast primitive draw-commands ‣ maybe even support for images?
40. hello <canvas>-API ‣ stable and fast ‣ even more features than we need ‣ works in every browser ‣ complete implementation for node.js available
 (via node-canvas npm module)
41. hello <canvas>-API var ws281x = require('rpi-ws281x'),
 canvas = ws281x.createCanvas(10,10),
 ctx = canvas.ctx;
 
 var c1 = new ws281x.Color('red'),
 c2 = new ws281x.Color('blue');
 
 function rnd(max) { return (max || 1) * Math.random(); }
 function rndi(max) { return Math.round(rnd(max)); }
 
 setInterval(function() {
 var c = ws281x.Color.mix(c1,c2, rnd());
 
 ctx.clearRect(0,0,10,10);
 ctx.fillStyle = 'rgb(' + c.rgb.join(',') + ')';
 ctx.fillRect(rndi(10)-2, rndi(10)-2, rndi(10), rndi(10));
 
 canvas.render();
 }, 1000/5);
42. <canvas>-API ‣ did I say this works in the browser? ‣ let's add a WebSocket and do this…
43. thank you! come to me if you have any questions… <3 Martin Schuhfuss – @usefulthink