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--- led_pwm_control [2017/01/23 17:27] – created walkeradmin
+++ led_pwm_control [2017/01/23 19:01] – [LED States] walkeradmin
@@ Line 1: / Line 1: @@
 ====== LED PWM Control ======
+<color #db5f0b>Jan 2017</color>
+\\
+----
+Turning on LEDs using the GPIO on the Raspberry Pi is pretty simple. You just turn on or off the relevant GPIO pin, and your LED (connected via a 330r resistor) will come on and go off.
+\\
+\\
+This is great until you want to control the brightness of the LED. You can control the LED Brightness using timers in Python (the slower/faster you pulse the GPIO, the brightness changes). There are a few issues though:
+\\
+\\
+As you slow the frequency, the LED flickers.
+As you speed up the LED, it does eventually start to dim, but uses all the Pi cpu resources (well on zero it does).
+\\
+\\
+So the most elegant solution is to use the PWM function. Its very simple to use, however there are only a couple of pins on the GPIO that support it. This is hardware based PWM, so it doesn't consume CPU resource.
+\\
+\\
+----
+==== Using PWM from the Command Line ====
+\\
+I have not used this in Python yet, so for now I am doing it from the command line, using the [[gpio_control_from_command_line|WiringPi]] libraries. Check out the [[gpio_control_from_command_line|WiringPi]] page if you need to set this up (takes about 20 seconds).
+\\
+\\
+I found this information regarding the Raspberry Pi GPIO for the Pi2. I have not found the same information for the Pi 3 yet.
+\\
+\\
+----
+There are two hardware PWM channels on the BCM2385/6.
+\\
+\\
+PWM0, which can be set to use GPIOs 12, 18, 40, and 52. Only 12 (pin 32) and 18 (pin 12) are available on the B+/2B, and PWM1 which can be set to use GPIOs 13, 19, 41, 45 and 53. Only 13 is available on the B+/2B, on pin 35 (but I think PWM1 is used for something - is it the audio output?)
+----
+\\
+For this example I am going to use GPIO12 (or Physical Pin32).
+\\
+\\
+The steps to use the GPIO in PWM mode are very simple:
+\\
+\\
+  * Setup the Pin as an Output
+  * Setup the Pin in PWM Mode
+  * Start the PWM
+----
+==== Setup the GPIO Pin as an Output ====
+\\
+For this we need to just type in the following line:
+\\
+    gpio -g mode 12 out
+\\
+This sets the mode to Output
+\\
+----
+==== Set the GPIO Pin Mode to PWM ===
+\\
+    gpio -g mode 12 pwm
+\\
+This sets the GPIO Pin mode to PWM.
+\\
+----
+==== Set the PWM Frequency ====
+\\
+The PWM frequency is a 10 Bit number, so has a range of 0-1023
+\\
+    gpio -g pwm 12 50
+\\
+The Higher the number, the brighter the LED. Simple.
+\\
+\\
+----
+==== LED States ====
+\\
+{{:led_001.jpg?125|}}{{:led_010.jpg?125|}}{{:led_050.jpg?125|}}{{:led_100.jpg?125|}}{{:led_250.jpg?125|}}{{:led_500.jpg?125|}}{{:led_999.jpg?125|}}
+\\
+\\
+----------PWM-001------------PWM-010------------PWM-050------------PWM-0100--------------PWM-250--------------PWM-500--------------PWM-999------------