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--- gpio_inputs_-_button_led_control [2016/08/09 20:33] – walkeradmin
+++ gpio_inputs_-_button_led_control [2023/03/09 22:35] (current) – external edit 127.0.0.1
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 In this section we will look at how to create an input pin, that is a GPIO pin that looks for an input (which will be a voltage). When we talk about voltages, the Raspberry Pi only sees a voltage in terms of an on (3.3v) or off (0v). However, other voltages will fall in to either the on or off state, and roughly speaking, these are:
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     Off =   0v - 1.2v
      On = 1.3v - 3.3v
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 **Remember, the GPIO pins are 3.3v as they are logic devices, attach more than 3.3v and you might have to buy a new Raspberry Pi!**
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+\\
+\\
+==== Pull Up, Pull Down ====
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+As we know, the value of a GPIO pin can be between 0v - 3.3v, this is a bit of a problem, because we need a pin to be at a known value so we don't get false positives, for this reason the Pi GPIO actually has built in Pull Up and Pull down resistors.
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+{{:pulluppulldown.png?400|}}
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+So for any input that we are waiting for a high signal (3.3v) we will use pull down so it stays a 0v, for any pin we are waiting for a low signal (0v) we will use a pull up so it stays at 3.3v (until a button press makes it low)
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+\\
+If you are using your Raspberry Pi via SSH or a Remote Desktop session, you need to enable remote access of the GPIO Pins, instructions for this are [[enable_remote_access_to_gpio_pins|here]]:
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+From the command line, create a new file for editing:
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+    sudo nano LED-Button.py
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+** You can download the code {{ :led-button.zip |Here}}: **
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+    #import modules
+    import RPi.GPIO as GPIO    # This imports the GPIO libarary that allows the use of the GPIO pins,
+                               # These libraries are built in to Raspbian.
+    GPIO.setmode (GPIO.BOARD)  # This sets the GPIO pin numbering. Our LED is connected to Pin 12,
+                               # so we can reference it by using BOARD as pin 12. However there is
+                               # another option (BCM) where we can reference a pin by it's name, pin
+                               # 12 is called GPIO18 (a reference to its place on the chip).
+    GPIO.setup(11, GPIO.IN, pull_up_down=GPIO.PUD_DOWN) # setup GPIO Pin 11 as an input, and set
+                                                        # the resistor to Pull Down (PUD_DOWN)
+                                                        # this is the pin the button is connected to
+                                                        # button is connected from pin 11 to the
+                                                        # +3.3v pin on the GPIO
+    GPIO.setup(12, GPIO.OUT)   # Sets the GPIO pin as output. This is connected to the LED, then
+                               # from the LED to 0v via a 330 Ohm resistor.
+    GPIO.output(12, 0)         # sets the GPIO Pin 12 to low (so 0v)
+    try:
+            while True:                             # start a loop
+                    if (GPIO.input(11) == 0):       # if GPIO pin 11 is a 0 (Low (0v)) then..
+                            GPIO.output(12,0)       # set Pin 12 to 0v (LED Stays off)
+                    else:                           # if GPIO pin is anything other than High (3.3v) then..
+                            GPIO.output(12,1)       # set Pin 12 to 3.3v (LED comes on)
+    except KeyboardInterrupt:                       # if Ctrl-C is pressed, exit loop
+            GPIO.cleanup()                          # reset GPIO pins to default state
+    #End
+\\
+\\
+==== The Button in Action ====
+Here is the button turning on the LED {{:led-button.mp4|950x574|autoplay,loop}}
+\\
+\\
+==== A Small Issue ====
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+While this code works without any real problems, because we are in a constant loop, this code is very heavy on CPU load, on the Pi Zero I am using this causes the processer to sit at 100 %, a better method is to use an **interrupt**
+\\
+\\
+This guide is comprised of information from a youtube video by **Gaven MacDonald**. Thanks Gaven.
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