151 lines
7.1 KiB
Markdown
151 lines
7.1 KiB
Markdown
Tutorial 1 - breadboard keyboard
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================================
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In this tutorial, you will build a breadboard keyboard with 4 keys.
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The keyboad will be used in tutorials 2 through 7.
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When you finish this tutorial you will have a working keyboard and an understanding of how a key matrix works.
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Why a solderless breadboard keyboard is useful
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----------------------------------------------
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Breadboard keyboards have key matrices and diodes just like the big keyboards.
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A breadboard is the easiest way to learn keyboard electronics.
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Learning is fun when mistakes are easily corrected.
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Compared to PCBs, breadboard keyboards make learning faster because:
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* Mistakes are easily corrected; no soldering and desoldering
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* Parts can be reused in many different configurations
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* A small keyboard is easier to trouble shoot
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Breadboard keyboards are useful for:
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* learning keyboard electronics - microcontroller, key matrix, diode, shift registers, I/O expander
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* learning the firmware development workflow
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* prototyping circuits before making a PCB
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Breadboard keyboard starter kit
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-------------------------------
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The parts needed to build the tutorial breadboard keyboards are listed in [breadboard_keyboard_supplies.ods](breadboard_keyboard_supplies.ods).
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The tutorials use a Teensy LC controller, but any Arduino-compatible controller with at least 2 KB SRAM should work.
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You will need two tools:
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* Wire cutters
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* A multi-meter for trouble shooting
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Wire striper, lead-forming tool, and Anti-static mat are optional.
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How a breadboard works
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To understand the breadboard keyboard you will need to know the internal parts of a breadboard:
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* bus strip
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* terminal strip
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These are explained in [How to Use a Breadboard](https://learn.sparkfun.com/tutorials/how-to-use-a-breadboard)
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Electrostatic discharge (ESD) safety
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------------------------------------
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Static electricity can damage a microcontroller in ways that are hard to trouble shoot.
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I live in a desert on a carpeted floor and get zapped by door knobs regularly.
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Here is the ESD precaution I take whenever I handle a microcontroller:
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1. Touch the bare metal on the back of my desktop computer (its grounded).
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2. Then touch the metal USB connector case on the microcontroller.
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Anti-static mat or anti-static wristband are also effective.
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Being tethered by an anti-static wristband can be inconvenient (wireless antistatic wrist straps are a scam).
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Not everyone needs to take ESD precautions:
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* http://forum.arduino.cc/index.php?topic=4643.0
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* https://forums.adafruit.com/viewtopic.php?f=8&t=12128
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Building a basic breadboard keyboard
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------------------------------------
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The basic breadboard keyboard has 4 switches.
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A Teensy LC microcontroller is on the left.
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A key matrix with 4 switches is to the right.
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The key matrix has two two columns.
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Short wires connect terminal strips into matrix columns.
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Jumper wires connect the columns to the microcontroller.
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Two bus strips are used as matrix rows.
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A jumper connects the top row to the microcontroller.
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A short wire connects the bottom row to the microcontroller.
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Switch-diode pairs, in series, connect rows to columns.
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Tutorials 2 and 3 use the same basic breadboard keyboard pictured above.
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Tutorials 4, 5, and 6 add more components to the basic breadboard keyboard.
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Positioning components as shown in the picture will provide space for those components.
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Breadboard keyboard assembly instructions:
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1. Shape leads to fit breadboard.
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* cut tactile-switch leads to length
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* bend and cut diode leads (save the cut offs for steps 2, 3, and tutorial 4)
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2. Insert parts into the breadboard as shown in the picture.
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* The breadboard is oriented with the red bus strips on top and blue bus strips on the bottom
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(this is important because tutorials will refer to the "red bus" and the "blue bus")
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* Teensy LC is on the left
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* switch leads are oriented to connect diodes to columns (pictured below)
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* diode cut offs connect terminal strips into columns
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* diodes connect switches to rows; orient diodes with cathode (banded end) towards the row (blue bus)
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3. Insert jumper wires to connect Arduino pins to the matrix rows and columns.
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* [Teensy LC pinout diagram](https://www.pjrc.com/teensy/card6a_rev2.png).
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* row_0 is the top row, and col_0 is the left column
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| Pin number | Connects to |
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|------------|-------------|
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| 0 | row_0 |
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| 1 | row_1 |
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| 14 | col_0 |
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| 15 | col_1 |
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Compiling and loading the keyboard firmware
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-------------------------------------------
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Follow the [keybrd Library User's Guide](../doc/keybrd_library_user_guide.md) to set up the Arduino environment.
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Compile and load the [keybrd_1_breadboard.ino](/tutorials/keybrd_1_breadboard/keybrd_1_breadboard.ino) sketch into the keyboard's controller.
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The operating system will take 1 to 6 seconds to recognize the USB keyboard.
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Then pressing the keys should type the characters 1, 2, a, b.
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Congratulations, you have a working keyboard.
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How a key matrix works
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----------------------
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Now we fill in some details of how it all works.
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This excellent article explains how key matrix, diodes, and ghosting work:
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[How a Key Matrix Work](http://pcbheaven.com/wikipages/How_Key_Matrices_Works/)
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In the article:
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> Output pins power columns and input pins detect the power on rows.
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The breadboard keyboards in this series of tutorials do it the other way:
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> Output pins power rows and input pins detect the power on columns.
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The keybrd library uses the word "strobe", which means powering one row for a very short time.
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Strobe pins are output pins connected to rows.
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One row at a time is strobed for the purpose of reading input pins.
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Exercises
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---------
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1) replace the diodes with wires (cutoffs) and intentionally cause ghosting.
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<br>
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<a rel="license" href="https://creativecommons.org/licenses/by/4.0/"><img alt="Creative Commons License" style="border-width:0" src="https://licensebuttons.net/l/by/4.0/88x31.png" /></a><br /><span xmlns:dct="http://purl.org/dc/terms/" property="dct:title">keybrd tutorial</span> by <a xmlns:cc="https://creativecommons.org/ns" href="https://github.com/wolfv6/keybrd" property="cc:attributionName" rel="cc:attributionURL">Wolfram Volpi</a> is licensed under a <a rel="license" href="https://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution 4.0 International License</a>.<br />Permissions beyond the scope of this license may be available at <a xmlns:cc="https://creativecommons.org/ns" href="https://github.com/wolfv6/keybrd/issues/new" rel="cc:morePermissions">https://github.com/wolfv6/keybrd/issues/new</a>.
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