Qwiic Keypad Hookup Guide

Introduction

Keypads are very handy input devices, but who wants to tie up 7 GPIO pins, wire up a handful of pull-up resistors, and write firmware that wastes valuable processing time scanning the keys for inputs? Let’s make the development process easier! The SparkFun Qwiic Keypad comes fully assembled and uses the simple Qwiic interface. No soldering, no voltage translation, no figuring out which I²C pin is SDA or SCL, just plug and go!

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SparkFun Qwiic Keypad - 12 Button

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The SparkFun Qwiic Keypad comes fully assembled and makes the development process for adding a 12 button keypad easy.

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The Qwiic Keypad reads and stores the last 15 button presses in a First-In, First-Out (FIFO) stack, so you don’t need to constantly poll the keypad from your microcontroller. This information, then, is accessible through the Qwiic interface. Qwiic Keypad even has a software configurable I²C address so you can have multiple I²C devices on the same bus.

Required Materials

The SparkFun Qwiic Keypad does need a few additional items for you to get started; a Qwiic enabled microcontroller and a Qwiic cable. You may already have a few of these items, so feel free to modify your cart based on your needs.

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SparkFun RedBoard Qwiic

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Additional Hardware for Example 5

Note: If you want to do the Example 5, then you will need to solder and connect a wire to the INT and Pin 2 on the RedBoard Qwiic. You may already have a few of these items, so feel free to modify your cart based on your needs.

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Suggested Reading

If you're unfamiliar with jumper pads or I²C be sure to checkout some of these foundational tutorials.

Additional Reading for Example 5

The Qwiic Keypad utilizes the Qwiic connect system. We recommend familiarizing yourself with the Logic Levels and I²C tutorials (above) before using it. Click on the banner above to learn more about our Qwiic products.

Hardware Overview

Keypad

This is a basic 12 button keypad that has been designed for easy user input and functionality. The buttons are set up in a matrix format. This allows the ATtiny84 to scan the 7 output pins to see which of the 12 buttons are being pressed.

Each of the keypad's 12 buttons has been labeled 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, *, and # and has been formatted to into the same layout as a telephone keypad. Each keypress resistance ranges between 10 - 150Ω.

Power LED

There is a power status LED to help make sure that your Qwiic Keypad is getting power. You can power the board either through the polarized Qwiic connector system or the breakout pins (PWR and GND) provided. The Qwiic system is meant to run on 3.3V, be sure that you are NOT using another voltage when using the Qwiic system. Qwiic Keypad is very low power and uses less than 4mA at 3.3V.

ATtiny84

With the pre-installed firmware, the ATtiny84 acts as an intermediary (microcontroller) multiplexing the buttons for inputs. This allows the Qwiic Keypad to store the button presses in the FIFO stack to be read over I²C. Although the ATtiny84 has a wide voltage range, since this is a Qwiic product, users should power the board with the labeled 3.3V.

First-In, First-Out (FIFO) Stack

In the firmware, the FIFO stack stores the most recent 15 button inputs. Once the stack is full, any previous inputs are overwritten. The FIFO stack is manually incremented using the FIFO Command register. If there are no more values stored in the FIFO stack, the output will be 0x00 or Null.

Qwiic and I²C

I²C Address

In the firmware, the Qwiic Keypad’s I²C address is configurable so you can add a bunch of them to the same bus without collision issues.

Factory Default I²C Slave Address: 0x4B

I²C Registers

Connections

The simplest way to use the Qwiic Keypad is through the Qwiic connect system. The connectors are polarized for the I²C connection and power. (*They are tied to their corresponding breakout pins.)

However, the board also provides six labeled breakout pins. You can connect these lines to the I²C bus of your microcontroller and power pins (3.3V and GND), if it doesn't have a Qwiic connector. The interrupt and reset pins are also broken out to use for triggered events.

Interrupt Pin

The interrupt pin (active low) is used to indicate that there are available entries in the FIFO stack. Effectively, if it is tied to an interrupt on your microcontroller and you are using it to increment the FIFO stack, then it will get triggered every time a button is pressed. The INT pin is pulled up with a 4.7kΩ resistor and will be low if there are entries. The INT pin will return high once the FIFO has been cleared.

Reset Pin

Reset pin tied to the reset pin on the ATtiny. When pulled low, this will effectively reset the Qwiic Keypad and restart the device, loading the I²C address that was stored in EEPROM. It is mostly, broken out for reprogramming the ATtiny84.

Jumpers

There are jumpers on the board allowing the user to select between different I²C addresses as well as to remove the pull up resistors from the I²C pins, if needed.

I²C Address

Bridging the I²C address jumper changes the slave address from the value stored in EEPROM to the I²C Jumper Default (or alternate): 0x4A.

• Open/Cut: Factory or Set I²C Slave Address: 0x4B (Factory Set) or 0x## (User Set)
• Bridged: I²C Jumper Default Slave Address: 0x4A (Alternate)

I²C Pull-Up

Cutting the I²C jumper will remove the 2.2kΩ pull-up resistors from the I²C bus. If you have many devices on your I²C bus you may want to remove these jumpers. Not sure how to cut a jumper? Read here!

Hardware Assembly

With the Qwiic connector system, assembling the hardware is simple. All you need to do is connect your Qwiic Keypad to Qwiic enabled microcontroller with a Qwiic cable. Otherwise, you can use the I²C pins, if you don't have a Qwiic connector on your microcontroller board. Just be aware of your input voltage and any logic level shifting you may need to do.

Arduino Library

The easiest way to install the Arduino library is by searching SparkFun Qwiic Keypad inside the Arduino library manager. To manually install, head on over to the GitHub repository or feel free to download the library here!

Library Functions

The Arduino library is commented and the functions should be self-explanatory. However, below is a detailed list of the available library functions.

.begin() or .begin(Wire, deviceAddress)
Creates a connection to an I²C device over the I²C bus using the default or specified I²C address.

.isConnected()
Tries to connect to the device at the I²C address stored in the library.

.getVersion()
Returns a string of the firmware version number.

.setI2CAddress(newAddress)
Changes the I²C address to newAddress. Once changed, the new I²C address is saved in the EEPROM of the Qwiic Keypad. Reconnects to device using new I²C address. (The new address is printed out in the Serial Monitor.)

.getButton()
Returns the button at the top of the stack (aka the oldest button). In order to read this register for the first time, the FIFO needs to be incremented with the .updateFIFO() function first.

.getTimeSincePressed()
This function reads the register that holds the time since the button (at the top of the FIFO stack) was pressed. In the firmware, the ATtiny85 actually responds to a request event (register read) and calculates the time since the button was pressed at that moment and updated the register. Like the .getButton() function, in order to use this function for the first time, the FIFO needs to be incremented with the .updateFIFO() function first.

.updateFIFO()
Used to increment the FIFO stack- In the library, this function sets the updateFIFO register to 0x01. Once there is a request event (i.e .getButton() or .getTimeSincePressed()), the FIFO is incremented and the firmware clears the updateFIFO register back to 0x00.

Examples

There are six examples in the Qwiic Keypad Arduino Library to get you started with using Qwiic Keypad. These example files are named with self-explanatory titles, but in case you want more information, see the descriptions below.

• Example1_ReadButton

  This example connects to the Qwiic Keypad using the default I²C address saved in the library. The sketch loops through reading the register for the button at the top of the FIFO stack and incrementing the FIFO. The example then prints out the value over the Serial Monitor. The * is represented by a space and the # is represented with a new line (or carriage return).

• Example2_ReadWithTime

  This example operates exactly like the Example1_ReadButton, except the time since the button was pressed is outputted with the button that was pressed in the Serial Monitor. With a ~1 second delay between checks for button presses.

• Example3_ChangeI2CAddress

  Caution: Will not work if I²C address jumper is bridged.

  This example connects to the Qwiic Keypad using the default I²C address set in the library and then prints out the I²C address and firmware version over the Serial Monitor. The sketch then, takes an input from the Serial Monitor to change the I²C address using a decimal value (DEC). Once the I²C address is changed, it is stored in the EEPROM of the Qwiic Keypad. After, the sketch connects to the keypad using the new I²C address and reads the registers for the firmware version again. The example then prints out those values over the Serial Monitor again.

• Example4_I2CScanner

  This example is from the I²C scanner example from the Arduino Playground webpage. The sketch scans for devices on the I²C bus and reports them on the Serial Monitor. This is useful for users who have forgotten the changed I²C address of their boards.

• Example5_InterruptRead

  Note: This example is requires soldering. A wire must be soldered to the INT pin and connected to an interrupt pin on your microcontroller. As written, the example assumes you are using a Arduino UNO based board, like our RedBoard. The sketch designates Pin 2 as the interrupt pin.

  This example operates exactly like the Example1_ReadButton, except that instead of constantly polling the keypad for button presses in the main loop, it responds to the interrupt (INT) pin. Utilizing an interrupt allows the MCU to execute a specific set of instructions (i.e. button read), outside of the main loop. For more details on interrupts, check out this tutorial on Processor Interrupts with Arduino .

• Example6_Keycode

  This example is a use case example, in which the user must input the correct key code: 1, 2, 3, 4. The sketch also implements a timeout, so that the user must input the correct code within 30 seconds.

Arduino Examples

Example 1: Read Button

The code for Example1_ReadButton connects to the Qwiic Keypad and prints out the value over the Serial Monitor. Below is a sample readout from the Serial Monitor using sequential button presses of: 1, 2, 3, 4, 5, 6, 7, 8, 9, *, 0, and #.

Example 2: Read with Time

The code for Example2_ReadWithTime operates exactly like the Example1_ReadButton, except the time between since the last button press is printed. Below is a sample readout.

Example 3: Change I²C Address

The code for Example3_ChangeI2CAddress connects to the Qwiic Keypad using the default I²C address set in the library and then prints out the I²C address and firmware version over the Serial Monitor. The sketch then, takes an input from the Serial Monitor to change the I²C address using a decimal value (DEC). Once the I²C address is changed, it is stored in the EEPROM of the Qwiic Keypad. After, the sketch connects to the keypad using the new I²C address and reads the registers for the firmware version again. The example then prints out those values over the Serial Monitor again. As shown in the sample readout below, the input value must between 8-119 (DEC) of unreserved I²C addresses.

Example 4: I²C Scanner

The forth example, Example4_I2CScanner, scans for devices on the I²C bus and reports them on the Serial Monitor. This is useful for users who have forgotten the changed I²C address of their boards.

Example 5: Read with Interrupt Pin

The code for Example5_InterruptRead operates similar to Example1_ReadButton, except that instead of constantly polling the keypad for button presses in software, it responds to a hardware trigger on the interrupt (INT) pin. For more details on interrupts, check out this tutorial on Processor Interrupts with Arduino .

Example 6: Key in Code

The last example, Example6_Keycode, is a use case example, in which the user must input the correct key code: 1, 2, 3, 4.

Resources and Going Further

For more information, check out the resources below:

• GitHub Product Repo
• Schematic (PDF)
• Eagle Files (ZIP)
• Keypad Pinout
• SparkFun Qwiic Keypad Arduino Library GitHub Repository
• SparkFun Qwiic Keypad Python Package GitHub Repository
• SFE Product Showcase

Need help getting started with Arduino and I²C? Check out these resources here:

• Arduino I²C Scanner Example
• Arduino Wire Library Reference Page
• Arduino Wire Library (In-Depth) Reference

Need some inspiration for your next project? Check out this Hotkey Project, similar to this blog post by ALEX THE GIANT from a few years ago.

Check out some of these other Qwiic product tutorials:

Or check out this blog post.