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diff --git a/posts/wifi-led-driver/index.html b/posts/wifi-led-driver/index.html new file mode 100644 index 0000000..c7b8053 --- /dev/null +++ b/posts/wifi-led-driver/index.html @@ -0,0 +1,183 @@ +<!DOCTYPE html> +<html lang="en-us"> + <head> + <meta charset="utf-8"> + <meta name="viewport" content="width=device-width, initial-scale=1"> + <title>Wifi Led Driver | blog.jaseg.de</title> + <link rel="stylesheet" href="/css/style.css" /> + <link rel="stylesheet" href="/css/fonts.css" /> + + <header> + <nav> + <ul> + + + <li class="pull-left "> + <a href="https://blog.jaseg.de/">/home/blog.jaseg.de</a> + </li> + + + + + </ul> + </nav> +</header> + + </head> + + <body> + <br/> + +<div class="article-meta"> +<h1><span class="title">Wifi Led Driver</span></h1> + +<h2 class="date">2018/05/02</h2> +<p class="terms"> + + + + + +</p> +</div> + + + +<main> +<div class="document"> + + +<div class="section" id="project-motivation"> +<h2>Project motivation</h2> +<!-- FIXME finished project picture with LED tape --> +<figure> + <img src="images/board_in_case.small.jpg"> + <figcaption>The completed driver board installed in the 3D-printed case. This device can now be connected to + 12V and two segments of LED tape that can then be controlled trough Wifi. The ESP8266 module goes on the pin + header on the left and was removed for this picture. + </figcaption> +</figure><p>After the <a class="reference external" href="https://blog.jaseg.de/posts/multichannel-led-driver/">multichannel LED driver</a> was completed, I was just getting used to controlling LEDs at 14-bit resolution. +I liked the board we designed in this project, but at 32 channels it was a bit large for most use cases. Sometimes I +just want to pop a piece of LED tape or two somewhere, but I don't need a full 32 channels of control. I ended up +thinking that a smaller version of the 32-channel driver that didn't require a separate control computer would be +handy. So I sat down and designed a variant of the design with only 8 channels instead of 32 and an on-board <a class="reference external" href="https://en.wikipedia.org/wiki/ESP8266">ESP8266</a> +module instead of the <a class="reference external" href="https://en.wikipedia.org/wiki/RS-485">RS485</a> transceiver for WiFi connectivity.</p> +</div> +<div class="section" id="the-electronics"> +<h2>The Electronics</h2> +<p>The schematic was mostly copy-pasted from the 32-channel design. The PCB was designed from scratch. This time, I went +for a 5x7cm form factor to allow for enough room for all connectors and to give the <a class="reference external" href="https://en.wikipedia.org/wiki/ESP8266">ESP8266</a>'s WiFi antenna enough +space. The board has two 5-pin <a class="reference external" href="https://www.phoenixcontact.com/online/portal/de?uri=pxc-oc-itemdetail:pid=1757019&library=dede&tab=1">Phoenix-style</a> for two RGB-White (RGBW) tapes and one 2-pin <a class="reference external" href="https://www.phoenixcontact.com/online/portal/de?uri=pxc-oc-itemdetail:pid=1757019&library=dede&tab=1">Phoenix-style</a> connector for +12V power input. The control circuitry and the serial protocol are unchanged, but the <a class="reference external" href="http://www.st.com/resource/en/datasheet/stm32f030f4.pdf">STM32</a> now talks to an <a class="reference external" href="http://www.watterott.com/de/ESP8266-WiFi-Serial-Transceiver-Modul">ESP-01</a> +module running custom firmware.</p> +<p>The LEDs are driven using a <a class="reference external" href="http://www.ti.com/lit/ds/symlink/sn74hc595.pdf">74HC595</a> shift register controlling a bunch of <a class="reference external" href="http://aosmd.com/pdfs/datasheet/AO3400.pdf">AO3400</a> <a class="reference external" href="https://en.wikipedia.org/wiki/MOSFET">MOSFETs</a>, with resistors in front of +the <a class="reference external" href="https://en.wikipedia.org/wiki/MOSFET">MOSFETs</a>' gates to slow down the transitions a bit to reduce brighntess nonlinearities and <a class="reference external" href="https://en.wikipedia.org/wiki/Electromagnetic_interference">EMI</a> resulting from +ringing of the LED tape's wiring inductance.</p> +<p>The board has two spots for either <a class="reference external" href="https://en.wikipedia.org/wiki/Resettable_fuse">self-resettable fuses (polyfuses)</a> or regular melting-wire <a class="reference external" href="https://en.wikipedia.org/wiki/Fuse_(electrical)">fuses</a> in +a small <a class="reference external" href="https://en.wikipedia.org/wiki/Surface-mount_technology">SMD</a> package, one for each RGBW output. For low currents the self-resettable fuses should be okay but at higher +currents their <a class="reference external" href="http://m.littelfuse.com/~/media/electronics/datasheets/resettable_ptcs/littelfuse_ptc_16r_datasheet.pdf.pdf">trip times get long enough that they become unlikely to trip in time to save anything</a>, so plain old non-resettable fuses would be the way to go there.</p> +<!-- FIXME finished board photos --> +<!-- FIXME board with test tape picture --> +<figure> + <figure class="side-by-side"> + <img src="images/schematic.png"> + <figcaption> + The schematic of the driver board, with the ESP8266 on the top left, the STM32 microcontroller for LED + modulation below, the shift register in the middle and the LED drivers and outputs on the right. + <a href="resource/schematic_and_pcb.pdf">Download PDF</a> + </figcaption> + </figure><figure class="side-by-side"> + <img src="images/layout.png"> + <figcaption> + The board layout with the top side being visible. The top side contains the footprint for the ESP8266, the + microcontroller, fuses, filter cap, connectors and the shift register. The LEDs are connected on the left, + with one connector per LED tape segment. The power input connector is on the bottom right. The LED driver + MOSFETs are in small SOT-23 packages on the back of the board. Since this board is not intended for + super-high currents, the MOSFETs are adequately cooled just through the board's copper planes. + <a href="resource/schematic_and_pcb.pdf">Download PDF</a> + </figcaption> + </figure> +</figure><figure> + <img src="images/boards.small.jpg"> + <figcaption>The completed PCBs of this project (front) and the `multichannel LED driver`_ project the driver + circuitry was derived from (back). + </figcaption> +</figure></div> +<div class="section" id="the-firmware"> +<h2>The Firmware</h2> +<p>The <a class="reference external" href="http://www.st.com/resource/en/datasheet/stm32f030f4.pdf">STM32</a> firmware only had to be slightly modified to accomodate the reduced channel count since the protocol remains +unchanged. The ESP firmware is based on <a class="reference external" href="https://github.com/Spritetm/esphttpd">esphttpd</a> by <a class="reference external" href="http://spritesmods.com/">Spritetm</a>. The modifications to the webserver firmware are pretty +basic. First, the UART console has been disabled since I use the UART to talk to the STM32. The few bootloader messages +popping out the UART on boot are not an issue, since they're unlikely to contain the fixed 32-bit address prefix the +serial protocol requires for the <a class="reference external" href="http://www.st.com/resource/en/datasheet/stm32f030f4.pdf">STM32</a> to do anything.</p> +<p>Second, I added LED control by adding drivers for the serial protocol and a bunch of colorspace conversion functions. +When I first tested the prototype software, I noticed that color reproduction was extremely poor. When I just sent a +<a class="reference external" href="https://en.wikipedia.org/wiki/HSL_and_HSV">HSV</a> rainbow fade from a python command line, the result looked totally wrong. The fade did not seem to go at a constant +speed and some colors, in particular yellow, orange and greens, were not visible at all. The problem turned out to be a +stark mismatch of the red, green and blue channels of the LED tape and less-than-optimal color reproduction of the pure +colors. I decided to properly measure the LED tape's color reproduction so I could compensate for it in software. This +turned out to be an extremely interesting project, the details of which you can read in my <a class="reference external" href="https://blog.jaseg.de/posts/led-characterization/">LED characterization</a> +article.</p> +<p>Third, I updated the built-in websites with some ad-hoc documentation on how to use the thing and a basic interface for +LED control.</p> +<!-- FIXME screenshot of firmware website --> +</div> +<div class="section" id="making-an-enclosure"> +<h2>Making an enclosure</h2> +<p>To be actually useful, the driver needed a robust enclosure. Bare PCBs are nice for prototyping, but for actually +putting the thing anywhere it needs a case to protect it against random destruction.</p> +<p>The board has four mounting holes with comfortable spacing in its corners to allow easy mounting inside a 3D-printed +case. The case itself is described in an <a class="reference external" href="http://www.openscad.org/">OpenSCAD</a> script. To make it look a little nicer, a little 3D relief is laid +into the lid. The 3D relief is generated with a bit of blender magic. The source <a class="reference external" href="https://en.wikipedia.org/wiki/STL_(file_format)">STL</a> model is loaded into blender, then +blender's amazingly flexible rendering system is used to export a depth map of a projection of the model as a <a class="reference external" href="https://en.wikipedia.org/wiki/Portable_Network_Graphics">PNG</a> file. +This depth map is then imported as a triangle mesh into <a class="reference external" href="http://www.openscad.org/">OpenSCAD</a>.</p> +<p>For the relief to look good, I chose a rather high resolution for the depth map. This unfortunately leads to extreme +memory use and processing time on the part of <a class="reference external" href="http://www.openscad.org/">OpenSCAD</a>, but since I have access to a sufficiently fast machine that is +not a problem. Just be careful if you try opening the <a class="reference external" href="http://www.openscad.org/">OpenSCAD</a> file on your machine, <a class="reference external" href="http://www.openscad.org/">OpenSCAD</a> will probably crash +unless you're on a beefy machine or interrupt it when it starts auto-rendering the file.</p> +<p>The board is mounted into the enclosure using knurled insert nuts that are pressed into a 3D-printed hole using a bit of +violence.</p> +</div> +</div> +</main> + + <footer> + +<script> +(function() { + function center_el(tagName) { + var tags = document.getElementsByTagName(tagName), i, tag; + for (i = 0; i < tags.length; i++) { + tag = tags[i]; + var parent = tag.parentElement; + + if (parent.childNodes.length === 1) { + + if (parent.nodeName === 'A') { + parent = parent.parentElement; + if (parent.childNodes.length != 1) continue; + } + if (parent.nodeName === 'P') parent.style.textAlign = 'center'; + } + } + } + var tagNames = ['img', 'embed', 'object']; + for (var i = 0; i < tagNames.length; i++) { + center_el(tagNames[i]); + } +})(); +</script> + + + <div id="license-info"> + ©2020 by Jan Götte. 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