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@@ -40,7 +40,7 @@ This configuration has a few advantages:
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- there is no keyboard scan....which helps keep scan-noise out of the power supply; helpful in an audio environment
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- can easily be set to wake-on-interrupt, which means that you can power down between keystrokes
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-See [KeyBounce](#keyboard-bounce) below.
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+See [KeyBounce](#keyboard-debounce) below.
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Of course, this solution does not apply to a keyboard which has *rows* and *columns*.
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@@ -91,7 +91,7 @@ idle CPU pin can be programmed as a logic
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input, and have interrupts enabled.
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Once a logic "high" is sensed, the CPU pin can be changed to an A/D pin,
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and the voltage
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-measured (after a short pause). The 1nF capacitor helps with keyboard bounce;
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+measured (after a short pause). The 1nF capacitor helps with keyboard debounce;
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the time constant is ~10us.
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Of course, if the user presses multiple keys simultaneously, the measurement will correspond to the highest voltage on that chart.
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@@ -135,7 +135,7 @@ This scheme can be configured for interrupt triggering
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columns are set to input+pullup+interrupt.
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Any keypress will then pull at least one column line low. Once the
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interrupt is triggered, change to the logic described above, scan the keyboard
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-[over the [debounce period](#keyboard-bounce) and then restore they keyboard
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+[over the [debounce period](#keyboard-debounce) and then restore they keyboard
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to the "ready-for-interrupt" configuration.
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### 3x4 plus Ground [new design]
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@@ -264,6 +264,20 @@ can happen.
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[Here](keyboard.c) is some example code to illustrate this decode; in C;
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look for the symbol **FOUR_PIN**. Here is a working prototype. 
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+### Interrupts
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+
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+These small keypads can be scanned continuously; you probably want to revisit the
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+keypad every 50ms or so to make sure you don't miss any keypresses.
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+
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+Changing to an interrupt-driven scheme allows you to relax about missing any keys;
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+you are guaranteed to get an interrupt on each key press. It also allows you to
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+power down the system until a key is pressed.
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+
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+Most of the designs above allow for an interrupt-driven configuration. Simply
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+set the column pins as "input-pullup-interrupt".
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+
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+Bear in mind: if the user presses a 2nd key while the 1st key is still depressed,
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+an interrupt will *not* be generated.
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### Keyboard Debounce
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@@ -298,10 +312,6 @@ One involves using an SPI output and a shift register
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<https://hackaday.com/2015/04/15/simple-keypad-scanning-with-spi-and-some-hardware/>
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This design requires an external chip ($0.10), 8 diodes and 4 resistors.
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-### Interrupts
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-
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-
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-
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### Reading DIP switches
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