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Tutorial 6 - Active high
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Pull-up resistors
-----------------
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There are many sources that explain "pull-up resistors", so I won't repeat it here.
Here is a [good tutorial on Pull-up Resistors ](https://learn.sparkfun.com/tutorials/pull-up-resistors/what-is-a-pull-up-resistor ).
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Active low
----------
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Most the keyboards up to this point in the tutorial series have used active low with internal pull-up resistors.
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"Active low" means that if a switch is pressed (active state), the read pin is low.
When the switch is released (inactive state), the pull-up resistor pulls the read pin high.
Arduino boards have internal pull-up resistors, which saves on parts and labor compared to manually adding external pull resistors.
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To make a key matrix active low:
* Orient diodes with cathode (banded end) towards the strobe pins (row)
* Instantiate the scanner in the sketch with strobeOn LOW, like this:
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```
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Scanner_uC scanner(LOW, readPins, readPinCount);
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```
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Active high
-----------
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"Active high" means that if a switch is pressed (active), the read pin is high.
When the switch is released (inactive), the pull-down resistor pulls the read pin low.
Arduino boards do not have internal pull-down resistors.
If you want to use active low, you will have to add external pull-down resistors to the read pins.
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To make a key matrix active high:
* Add an external 10k Ohm pull-down resistor to each read pin
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* Orient diodes with cathode (banded end) towards the read pins
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* Instantiate the scanner in the sketch with strobeOn HIGH, like this:
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```
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Scanner_uC scanner(HIGH, readPins, readPinCount);
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```
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Making a breadboard keyboard active-high
----------------------------------------
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Make the following changes to the basic breadboard keyboard described in [tutorial_1_breadboard_keyboard.md ](tutorial_1_breadboard_keyboard.md ):
* Add an external 10k Ohm pull-down resistor (red bus) to each read pin
* Orient diodes with cathode (banded end) towards the read pins
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keybrd sketch with active-high
------------------------------
The [keybrd_6_active_high.ino ](keybrd_6_active_high/keybrd_6_active_high.ino ) sketch will run on the above breadboard keyboard.
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< br >
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