add toggleButton example

1_Basic_GPIO/digitalIn.md

@@ -24,3 +24,42 @@ The usual `gpio_init` and `gpio_set_dir` are used to initialize and set the dire
 The same code can be used for controlling the fan from earlier experiment. LED connected to the `ledPin` is replaced with connection to the gate pin of the mosfet.
 
 - insert gif of controlling fan with button
+
+## ToggleButton
+
+Instead of setting the fan status to be the same as the the button status, this example toggles everytime the button is pressed.
+
+Below code demonstrates using a button to toggle the state of the fan between on and off.
+
+```c
+    int buttonStatus = gpio_get(buttonPin);
+    bool outputStatus = false;
+    int state = buttonStatus * 2 + gpio_get(buttonPin);
+    while (true)
+    {
+        state = buttonStatus * 2 + gpio_get(buttonPin);
+        switch (state)
+        {
+        case 1:
+            outputStatus = !outputStatus;
+            gpio_put(ledPin, outputStatus);
+            buttonStatus = 1;
+            sleep_ms(10);
+            break;
+        case 2:
+            buttonStatus = 0;
+            sleep_ms(10);
+        default:
+            break;
+        }
+    }
+```
+
+To toggle the state on button state changes, change in button press is recorded using `buttonStatus` variable.
+
+If the button is pressed, `buttonState` will be `0` and new state will be `1`. Hence, the value in the `status` variable will be `1`. When this happens, the fan state is toggled. Output doesn't change when the button is released.
+
+
+Small delay is added to mitigate switch bouncing, as explained in [Circuit Basics blog on switch de-bouncing](https://www.circuitbasics.com/how-to-use-switch-debouncing-on-the-arduino/).
+
+ - insert gif of fan toggling.