RGBLEDs < AFNOG

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---+ RGB LEDs
---++ Introduction

When construction the <i>virtual world demo </i>we will use two different types of sensors
   * an RGB color sensor giving us the color of a paper sheet
   * an ultrasonic distance sensor determining the distance between the paper sheet and the sensor.
Before using this information however we will have to understand the sensors and their readout and as a preliminary experiment we will read the color of the paper sheet and light an rgb color LED with the same color. Switching to a paper sheet with a different color will also light the LED in the same different color.

There are quite a few different types of breakout boards implementing RGB LEDs on the market which have to connected to the controller in different ways. Most of them just consist of 3 LEDs of the base colors implemented in a single package. Some of the breakout boards however have the necessary current limiting resistors already on board while for others they must be provided externally.

There is also a type of "intelligent" LED where the RGB values are provided in a serial data stream.
| <p><img alt="" height="227" src="%ATTACHURL%/ky-009.png" width="326" /></p> <p>KY-009 SMD LED needing external resistors</p> | <p><img alt="" height="230" src="%ATTACHURL%/lilyPadTriColorLED.png" width="269" /></p> <p>Lily Pad Tri-Color LED</p> |
| <p><img alt="" height="236" src="%ATTACHURL%/2018-01-30-182614_520x384_scrot.png" width="320" /></p> <p>Standard 3 color LED with resistors on board</p> | <p><img alt="" height="240" src="%ATTACHURL%/rgbLED-1.png" width="327" /></p> <p>WS2812 "intelligent" LED</p> |
For you information, here is the [[http://www.seeedstudio.com/document/pdf/WS2812B%20Datasheet.pdf][WS2812 data sheet]]
---++ Programming the LEDs

It is an excellent introductory exercise to try programming the LEDs and we will go about it in steps. First the device must be connected to the Raspberry Pi controller which is done through the cobbler and the bread board. Depending on the breakout board used we will need additional external 330 Ohm resistors on each of the color components (KY-009). Then we connect as follows:
   * - -&gt; Gnd
   * red -&gt; gpio 18
   * green -&gt; gpio 17
   * blue -&gt; gpio 22
This cabling is of course only true for the KY-009 and the "standard rgd LED". In contrast to these devices which have a common cathode the !LilyPad has a common anode and must be connect to Vcc instead of Gnd. The WS2812 is complete different and is programmed with a serial protocol. To check the device we can temporarily connect these pins to Vcc (or ground in case of the Lily Pad, make sure the current limiting resistor is there, either on the breakout board or externally added by you) in which case we should see the corresponding color come up on the LED. Once connected to the gpio pins we can start programming.

Making a LED light up is one of the most simple programming exercises possible and therefore ideally suited to get us going with Python programming.

The following programs work for common cathode LEDs (KY-009 and Standard 3 color LED) only for which the GND pin is common. For Common Anode LEDs, which have a common Vcc like the the Lily Pad one you must pull the individual red, green, blue pins low to make the LED light up.

| <img alt="" height="267" src="%ATTACHURL%/commonCathode.png" width="219" /> | <img alt="" height="267" src="%ATTACHURL%/commonAnode.png" width="224" /> |
 

Three programs will be developed with increasing difficulty:
   * [[%ATTACHURL%/rgbLED.py.txt][rgbLED.py]] uses 3 bit binary numbers, where each bit corresponds to one of the three LEDs. A total number of 7 (+ all LEDs dark) can be displayed this way. First the [[http://abyz.me.uk/rpi/pigpio/python.html][pigpio library ]]is included and then the connections to the gpio pins defined and each of these pins set to OUTPUT. Then we switch the LEDs on, where the binary number 001 means that only <span class="WYSIWYG_COLOR" style="color: darkgreen;">green</span> is on, 010 only%RED% red%ENDCOLOR% is on 100 only %BLUE%blue%ENDCOLOR% is on. A combination of bits like 011 or 110 mean a combination of %GREEN%green%ENDCOLOR% and %RED%red%ENDCOLOR% or %RED%red%ENDCOLOR% and %BLUE%blue %ENDCOLOR%respectivly.
   * [[%ATTACHURL%/fullColors.py.txt][fullColors.py]] is a program that changes the light intensity from total dark to full color intensity for each of the 3 LEDs using %BLUE%P%ENDCOLOR%ulse %BLUE%W%ENDCOLOR%idth %BLUE%M%ENDCOLOR%odulation (PWM).
   * [[%ATTACHURL%/rgbColorIntensities.py.txt][rgbColorIntensities.py]] finally combines both methods and allows the user to define an arbitrary color by entering rgb values through the command line.
You may download the file [[%ATTACHURL%/rgbLED.tar.gz][rgbLED.tar.gz]] containing all three programs.

-- %USERSIG{UliRaich - 2018-01-30}%

---++ Comments

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Attachments

Topic attachments
I	Attachment	History	Action	Size	Date	Who
png	2018-01-30-182614_520x384_scrot.png	r1	manage	143.8 K	2018-01-30 - 17:27	UliRaich
png	commonAnode.png	r1	manage	23.7 K	2018-03-06 - 13:30	UliRaich
png	commonCathode.png	r1	manage	23.7 K	2018-03-06 - 13:30	UliRaich
txt	fullColors.py.txt	r1	manage	0.7 K	2018-01-30 - 19:24	UliRaich
png	ky-009.png	r1	manage	145.5 K	2018-01-30 - 17:15	UliRaich
png	lilyPadTriColorLED.png	r1	manage	152.5 K	2018-01-30 - 17:15	UliRaich
txt	rgbColorIntensities.py.txt	r1	manage	1.0 K	2018-01-30 - 19:24	UliRaich
png	rgbLED-1.png	r1	manage	128.6 K	2018-01-30 - 17:15	UliRaich
txt	rgbLED.py.txt	r1	manage	0.6 K	2018-01-30 - 19:24	UliRaich
gz	rgbLED.tar.gz	r1	manage	0.7 K	2018-01-30 - 19:26	UliRaich

Topic revision: r5 - 2018-03-06 - UliRaich