How keyboards are made? This has been already discussed in Atmega 32u4 based Generic USB Keyboard project. A number pad is also a kind of keyboard having the keys for decimal digits and the basic arithmetic operations. Building from the keyboard project, a basic numeric keypad that will work with all the operating systems is designed in the following project. The keypad will have ten keys for the decimal digits and one key for multiplication, division, subtraction, addition and equals each. Each of these digits or operations has unique keycode assigned. The project utilizes 8-bit USB AVR – Atmega 32u4 as the USB controller chip to pass the keycodes to the computer in a format dictated by the USB protocol and uses AVR based Lightweight USB Framework (LUFA) as the firmware to implement the protocol itself.

Fig. 1: Prototype of Arduino Based USB Number Keypad 

The LUFA firmware is used and its HID device driver class for keyboard is modified to program the project. The numeric keypad has the keys for the following tasks – :

• Ten Digit Keys (0-9)

• Addition

• Subtraction

• Multiplication

• Division

• Equals

This number pad can be used with any USB enabled computing device and any operating system. The project uses tactile switches as keypad buttons, Atmega 32u4 as the controller chip (on board Arduino Pro Micro) and USB cable to connect with the personal computer.

PREREQUISITES

This project is based on Arduino Pro Micro which has the USB AVR – Atmega 32u4 as the sitting MCU. In order to understand this project, one must have basic knowledge of the AVR microcontrollers and the embedded C programming for AVRs. WinAVR Studio is used to write, edit and compile the project code, so closely following the project shall require familiarizing with the above stated IDE as well. Though LUFA framework takes care of implementing the USB protocol and has APIs to abstract the lower level codes, understanding USB protocol is recommended to understand how actually the project is working. In fact, if anyone has already worked on some other microcontroller, it will not be much pain to understand and follow this project as the project code is more or less about getting input from the GPIO pins of AVR MCU and modifying the LUFA device driver of generic keyboard accordingly.

Fig. 2: Image demonstrating working of Arduino Based USB Number Keypad 

COMPONENTS REQUIRED

1. Arduino Pro Micro

2. Breadboard

3. Connecting wires

4. Push buttons

5. Micro USB cable

6. 10K resistors

SOFTWARE TOOLS REQUIRED

1. WinAVR Studio

2. AVR Dude

3. LUFA Firmware

BLOCK DIAGRAM

Fig. 3: Block Diagram of Arduino Based USB Number Keypad 

CIRCUIT CONNECTIONS

The project uses Arduino Pro Micro as the USB controller chip. A set of fifteen tactile switches is connected to the port B, D, and F of the Arduino. The switches are connected to pins 1, 2, 4, 5 and 6 of the port B, 0, 1, 2, 3, 4 and 7 of Port D and 4, 5, 6 and 7 of Port F with functions assigned to them according to the following table -:

Fig. 4: Table listing Arduino pins and respective keypad functions

The tactile switches are connected between the port and ground. The pins of port B by default are connected to VCC and receive a HIGH logic. Pressing a tactile switch changes the status at the respective pin to LOW by short circuiting to the ground.

The Program code for the project is burnt to the Arduino Pro Micro using AVR Dude. The Arduino board is connected to the USB port of a PC by a USB cable.

HOW THE PROJECT WORKS

For configuring the controller chip to work as a Keypad controller, the  HID Class Driver for keyboard of the LUFA framework is used. The Human Interface Device (HID) class takes care of the transfers between the host device and the human controlled USB peripherals like USB Keyboard, Mouse or Joystick. The implementation of the USB protocol is carried out by the open-source drivers  of the LUFA framework.

Like any HID device, when the numeric keypad is attached to the host computer (PC), the host sends request for configuration details in the form of control transfer. The controller chip on keypad has to respond with appropriate descriptors to get configured and ready for further operations. Only after configuration, the keypad can transfer user inputs with the host in the form of interrupt transfers for executing the numeric operations. The process of identification and configuration of any USB device with the host is called enumeration.

Fig. 5: Image showing number 0 typed from Arduino USB Keypad

Any device using HID class for keyboards identifies the key pressed by the keycode or combination of keycodes sent from the controller chip of the device to the host in the data input report. Any keyboard device sends a usage report and data input report to the host and receives data output report from the host at the application layer to work like a keyboard. The reports are a medium at application layer as per the USB protocol to facilitate enumeration and communication between the host and the device. To learn about HID Class for Keyboard and how the usage report, data input report and data output report are structured in the HID Class for Keyboard, go through the Atmega 32u4 based Generic USB Keyboard project. To learn about the keycodes assigned to different ASCII characters and modifier keys on a generic keyboard, check out the HID Usage Table provided by the USB Implementers Forum.

The keycode that have to be passed to the host on pressing a key is managed by the program code of USB controller chip. For this project, each key has a unique keycode which needs to be passed by the controller chip on detecting the pressing of respective button The buttons on the keypad passes the keycodes for the following keys.

Fig. 6: Table listing Arduino pins and respective keypad functions and keycodes

The numeric keypad is just a custom built keyboard. A keyboard is HID class USB device and LUFA framework has HID class related modules  in the LUFA-Source-Folder /LUFA/Drivers/USB/Class/Device folder. Other device class related module are also in the same folder. The LUFA framework has demo projects for different USB device classes in the LUFA-Source-FolderDemosDeviceClassDriver folder. For implementing the project, demo project for keyboard provided in the LUFA framework is modified and complied. The demo project for keyboard is in the LUFA-Source-FolderDemosDeviceClassDriverKeyboard folder. The folder contains keyboard.c file which will be modified to work for the numeric keypad.

How Keyboard.c identifies HID device being Keyboard

The keyboard.c uses Keyboard_HID_Interface interface in HID_Device_USBTask() function which is being imported from the HIDDeviceClass.c (from LUFA-Source-Folder LUFADriversUSBClassDevice) to configure the device as keyboard. The interface abstracts the low-level descriptor codes and identifies the device as keyboard through an InterfaceNumber variable.

From Where Keyboard.C gets the USAGE and Data Reports Descriptors

In the LUFA framework’s demo project for Keyboard, descriptor.c file is imported in keyboard.c to send the relevant usage and data reports descriptors to the host device. The descriptor.c defines a KeyboardReport[] structure  which is used in the CALLBACK_HID_Device_CreateHIDReport() function of the keyboard.c to generate keyboard specific usage and data reports descriptors. Inside descriptor.c the KeyboardReport[] structure has the values returned by HID_DESCRIPTOR_KEYBOARD () function. The HID_DESCRIPTOR_KEYBOARD() is defined in HIDClassCommon.h (located in LUFA-Source-FolderLUFADriversUSBClassCommon folder). The keyboard.c imports keyboard.h which imports usb.h. USB.h imports HIDCLass.h. In HIDClass.h is imported HIDClassDevice.h if the USB_CAN_BE_DEVICE is true for the controller chip to being a USB device not the host. The HIDClassDevice.h imports HIDClassCommon.h where the HID device specific descriptor fields have been defined.

HOW THE DEVICE WORKS

The AVR microcontroller is programmed to get the user inputs from the tactile switches that work as the keypad buttons. The main() function and CALLBACK_HID_Device_CreateHIDReport() function of the keyboard.c are modified to customize the program code to send the respective keycodes in the data input report. Check out the program code to see the modifications implemented for this numeric keypad.

Fig. 7: Image showing numerals typed from Arduino based USB Keypad

PROGRAMMING GUIDE

For building the project download the LUFA framework from the github.com. The demo project provided with the LUFA framework is modified to make this numeric keypad. In the extracted LUFA zip file, open Demos/Device/ClassDriver/Keyboard folder. The folder has the following files and folders.

Fig. 8: Screenshot of LUFA Library Folder on Windows

Of these, Keyboard.h, Keyboard.c and Makefile needs to be modified for this project. The modified files (provided at the bottom of the article in zip format) can also be downloaded from the engineersgarage and replaced with the original files. Either open the files in WinAVR Studio or Notepad++ and modify original files or replace files with the already modified one. The modified or replaced Keyboard.c needs to be compiled from within the LUFA’s Source folder to get the object code.

Modifying Keyboard.h

The Keyboard.h library file is imported in the Keyboard.c file and includes a set of additional libraries and defines the constants and functions for the keyboard device. These include the additional libraries for the joystick, button and LEDs which should be commented out as the project is not using these HID features. So open Keyboard.h and make the following changes – :

• Comment the #include library statements for Joystick.h, LEDS.h, and Buttons.h (The include statements for these libraries are commented as any joystick, buttons board and LED board is not used in the project)

Save the file with changes.

Modifying Keyboard.C file

Again in the Keyboard.c, the code sections for Joystick, button board and LEDs need to be commented out.  So open Keyboard.c and make the following changes – :

• In the main loop, comment the LEDs_SetAllLEDs()

• In SetupHardware() function, comment the Joystick_Init(), LEDs_Init(), Buttons_Init()

• In EVENT_USB_Device_Connect() function, comment the LEDs_SetAllLEDs()

• In EVENT_USB_Device_Disconnect() function, comment LEDs_SetAllLEDs()

• In EVENT_USB_Device_ConfigurationChanged() function, comment the LEDs_SetAllLEDs()

In Keyboard.c the main() function executes the functioning of the Keypad. Inside the main function, Port B, D and F where the tactile switches have been connected needs to be defined as input and all the pins of port B has to be raised to HIGH logic by default as the microcontroller will need to detect LOW logic for input from the tactile switches. Therefore, modify the body of main() function as the code given below.

Inside the infinite for loop the HID_Device_USBTask() function is called where Keyboard_HID_Interface interface is passed as parameter. The interface identifies the device as keyboard and abstracts the low level program code specific to keyboard HID class. The function is coming from the HIDClassDevice.c module (located in LUFA/Drivers/USB/Class/Device/HIDClassDevice.c) and is used for general management task for a given HID class interface, required for the correct operation of the interface. It should be called in the main program loop, before the master USB management task USB_USBTask(). The  USB_USBTask() is the main USB management task. The USB driver requires this task to be executed continuously when the USB system is active (device attached in host mode, or attached to a host in device mode) in order to manage USB communications. The function is defined in USBTask.c (Located in LUFA-Source-FolderLUFADriversUSBCore folder).

For creating Keyboard Data Input report to pass the keycodes according to the pressed keypad button CALLBACK_HID_Device_CreateHIDReport() needs to be modified. The default file has the function body to detect joystick movement as well.

Fig. 9: Screenshot of CALLBACK_HID_Device_CreateHIDReport Function of LUFA library

The numeric keypad is using tactile switches to get the hint of keycode that needs to be passed. Therefore, LOW bit at each button is detected and the corresponding keycode is sent via data input report for the keyboard HID Class. So replace the body of the CALLBACK_HID_Device_CreateHIDReport() function with the following code -:

In the body _BV() function is used to map the respective bit as a byte with only the respective bit changed in the returned byte. In the code, the constants to represent the following numeric keys are used (defined in HIDCommonClass.h, header file located in  LUFA-Source-FolderLUFADriversUSBClassCommon folder).

Fig. 9: Table listing keys and respective constants used in LUFA

The Data Output Report is not utilized in the project execution therefore the CALLBACK_HID_Device_ProcessHIDReport() function which process Data Output report has been kept unchanged.

Save the file and create Make file for the project.

Modifying Make File

In the Keyboard folder there is a make file that needs to be edited. The file can be edited using Notepad++. The following information needs to be edited –

• MCU = atmega32u4

• ARCH = AVR8

• BOARD = LEONARDO

• F_CPU = 16000000

Save the file and exit. Now all the files are edited completely for the numeric keypad project.

Compiling Keyboard.c

For compiling the source code, WinAVR Programmers Notepad or Arduino IDE can be used. Open the modified Keyboard.c file and compile the code.

BURNING HEX CODE

The hex file is generated on compiling the keyboard.c file. For burning the object code to microcontroller open the Command Prompt, change the current directory to the directory containing the Hex file. This can be done using command: CD <address of the directory>. Now reset the Arduino and instantly run the command: : avrdude -v -p atmega32u4 -c avr109 -P COM20 -b 57600 -D -Uflash:w:Keyboard.hex:i after replacing the COM Port with the recognized one.

If the uploading process is successful, the Arduino board will be shown as HID Keyboard in the Device Manager. There is no need of installing any driver in the computer as Generic HID Keyboard is used for the project implementation. Use the numeric keypad similar to number pad of any generic USB keyboard.

Project Source Code

###


/*

             LUFA Library
     Copyright (C) Dean Camera, 2015.
  dean [at] fourwalledcubicle [dot] com
           www.lufa-lib.org

*/
/*

  Copyright 2015  Dean Camera (dean [at] fourwalledcubicle [dot] com)
  Permission to use, copy, modify, distribute, and sell this
  software and its documentation for any purpose is hereby granted
  without fee, provided that the above copyright notice appear in
  all copies and that both that the copyright notice and this
  permission notice and warranty disclaimer appear in supporting
  documentation, and that the name of the author not be used in
  advertising or publicity pertaining to distribution of the
  software without specific, written prior permission.
  The author disclaims all warranties with regard to this
  software, including all implied warranties of merchantability
  and fitness.  In no event shall the author be liable for any
  special, indirect or consequential damages or any damages
  whatsoever resulting from loss of use, data or profits, whether
  in an action of contract, negligence or other tortious action,
  arising out of or in connection with the use or performance of
  this software.

*/

/** file

 *
 *  Main source file for the Keyboard demo. This file contains the main tasks of
 *  the demo and is responsible for the initial application hardware configuration.
 */


#include "Keyboard.h"


/** Buffer to hold the previously generated Keyboard HID report, 
for comparison purposes inside the HID class driver. */

static uint8_t PrevKeyboardHIDReportBuffer[sizeof(USB_KeyboardReport_Data_t)];


/** LUFA HID Class driver interface configuration and state information. This structure is

 *  passed to all HID Class driver functions, so that multiple instances of the same class

 *  within a device can be differentiated from one another.

 */

USB_ClassInfo_HID_Device_t Keyboard_HID_Interface =

{

.Config =

{

.InterfaceNumber              = INTERFACE_ID_Keyboard,

.ReportINEndpoint             =

{

.Address              = KEYBOARD_EPADDR,

.Size                 = KEYBOARD_EPSIZE,

.Banks                = 1,

},

.PrevReportINBuffer           = PrevKeyboardHIDReportBuffer,

.PrevReportINBufferSize       = sizeof(PrevKeyboardHIDReportBuffer),

},

};



/** Main program entry point. This routine contains the overall program flow, including initial

 *  setup of all components and the main program loop.

 */

int main(void)

{

SetupHardware();


DDRB = 0x00;

DDRD = 0x00;

DDRF = 0x00;

PORTB = 0xff;

PORTD = 0xff;

PORTF = 0xff;

//LEDs_SetAllLEDs(LEDMASK_USB_NOTREADY);

GlobalInterruptEnable();


for (;;)

{

HID_Device_USBTask(&Keyboard_HID_Interface);

USB_USBTask();

}

}


/** Configures the board hardware and chip peripherals for the demo's functionality. */

void SetupHardware()

{

#if (ARCH == ARCH_AVR8)

/* Disable watchdog if enabled by bootloader/fuses */

MCUSR &= ~(1 << WDRF);

wdt_disable();


/* Disable clock division */

clock_prescale_set(clock_div_1);

#elif (ARCH == ARCH_XMEGA)

/* Start the PLL to multiply the 2MHz RC oscillator to 32MHz and switch the CPU core to run from it */

XMEGACLK_StartPLL(CLOCK_SRC_INT_RC2MHZ, 2000000, F_CPU);

XMEGACLK_SetCPUClockSource(CLOCK_SRC_PLL);


/* Start the 32MHz internal RC oscillator and start the DFLL to increase it to 48MHz 
using the USB SOF as a reference */

XMEGACLK_StartInternalOscillator(CLOCK_SRC_INT_RC32MHZ);

XMEGACLK_StartDFLL(CLOCK_SRC_INT_RC32MHZ, DFLL_REF_INT_USBSOF, F_USB);


PMIC.CTRL = PMIC_LOLVLEN_bm | PMIC_MEDLVLEN_bm | PMIC_HILVLEN_bm;

#endif


/* Hardware Initialization */

//Joystick_Init();

//LEDs_Init();

//Buttons_Init();

USB_Init();

}


/** Event handler for the library USB Connection event. */

void EVENT_USB_Device_Connect(void)

{

//LEDs_SetAllLEDs(LEDMASK_USB_ENUMERATING);

}


/** Event handler for the library USB Disconnection event. */

void EVENT_USB_Device_Disconnect(void)

{

//LEDs_SetAllLEDs(LEDMASK_USB_NOTREADY);

}


/** Event handler for the library USB Configuration Changed event. */

void EVENT_USB_Device_ConfigurationChanged(void)

{

bool ConfigSuccess = true;


ConfigSuccess &= HID_Device_ConfigureEndpoints(&Keyboard_HID_Interface);


USB_Device_EnableSOFEvents();


//LEDs_SetAllLEDs(ConfigSuccess ? LEDMASK_USB_READY : LEDMASK_USB_ERROR);

}


/** Event handler for the library USB Control Request reception event. */

void EVENT_USB_Device_ControlRequest(void)

{

HID_Device_ProcessControlRequest(&Keyboard_HID_Interface);

}


/** Event handler for the USB device Start Of Frame event. */

void EVENT_USB_Device_StartOfFrame(void)

{

HID_Device_MillisecondElapsed(&Keyboard_HID_Interface);

}


/** HID class driver callback function for the creation of HID reports to the host.

 *

 *  param[in]     HIDInterfaceInfo  Pointer to the HID class 
interface configuration structure being referenced

 *  param[in,out] ReportID    Report ID requested by the host if non-zero, 
otherwise callback should set to the generated report ID

 *  param[in]     ReportType  Type of the report to create, 
either HID_REPORT_ITEM_In or HID_REPORT_ITEM_Feature

 *  param[out]    ReportData  Pointer to a buffer where the created report should be stored

 *  param[out]    ReportSize  Number of bytes written in the report (or zero if no report is to be sent)

 *

 *  return Boolean c true to force the sending of the report, 
c false to let the library determine if it needs to be sent

 */

bool CALLBACK_HID_Device_CreateHIDReport(USB_ClassInfo_HID_Device_t* const HIDInterfaceInfo,

                                         uint8_t* const ReportID,

                                         const uint8_t ReportType,

                                         void* ReportData,

                                         uint16_t* const ReportSize)

{

USB_KeyboardReport_Data_t* KeyboardReport = (USB_KeyboardReport_Data_t*)ReportData;



uint8_t UsedKeyCodes = 0;


  if(!(PIND & _BV(PD3))) { 

// add keycode for numeric 0 in the report

KeyboardReport->KeyCode[UsedKeyCodes++] = HID_KEYBOARD_SC_KEYPAD_0_AND_INSERT;

}

else if(!(PIND & _BV(PD2))) { 

// add keycode for numeric 1 in the report

KeyboardReport->KeyCode[UsedKeyCodes++] = HID_KEYBOARD_SC_KEYPAD_1_AND_END;

}

else if(!(PIND & _BV(PD1))) { 

// add keycode for numeric 2 in the report

KeyboardReport->KeyCode[UsedKeyCodes++] = HID_KEYBOARD_SC_KEYPAD_2_AND_DOWN_ARROW;

}

else if(!(PIND & _BV(PD0))) { 

// add keycode for numeric 3 in the report

KeyboardReport->KeyCode[UsedKeyCodes++] = HID_KEYBOARD_SC_KEYPAD_3_AND_PAGE_DOWN;

}

else if(!(PIND & _BV(PD4))) { 

// add keycode for numeric 4 in the report

KeyboardReport->KeyCode[UsedKeyCodes++] = HID_KEYBOARD_SC_KEYPAD_4_AND_LEFT_ARROW;

}

else if(!(PIND & _BV(PD7))) { 

// add keycode for numeric 5 in the report

KeyboardReport->KeyCode[UsedKeyCodes++] = HID_KEYBOARD_SC_KEYPAD_5;

}

else if(!(PINB & _BV(PB4))) { 

// add keycode for numeric 6 in the report

KeyboardReport->KeyCode[UsedKeyCodes++] = HID_KEYBOARD_SC_KEYPAD_6_AND_RIGHT_ARROW;

}

else if(!(PINB & _BV(PB5))) { 

// add keycode for numeric 7 in the report

KeyboardReport->KeyCode[UsedKeyCodes++] = HID_KEYBOARD_SC_KEYPAD_7_AND_HOME;

}

else if(!(PINB & _BV(PB6))) { 

// add keycode for numeric 8 in the report

KeyboardReport->KeyCode[UsedKeyCodes++] = HID_KEYBOARD_SC_KEYPAD_8_AND_UP_ARROW;

}

else if(!(PINB & _BV(PB2))) { 

// add keycode for numeric 9 in the report

KeyboardReport->KeyCode[UsedKeyCodes++] = HID_KEYBOARD_SC_KEYPAD_9_AND_PAGE_UP;

}

else if(!(PINB & _BV(PB1))) { 

// add keycode for dot in the report

KeyboardReport->KeyCode[UsedKeyCodes++] = HID_KEYBOARD_SC_KEYPAD_DOT_AND_DELETE;

}

else if(!(PINF & _BV(PF7))) { 

// add keycode for - in the report

KeyboardReport->KeyCode[UsedKeyCodes++] = HID_KEYBOARD_SC_KEYPAD_MINUS;

}

else if(!(PINF & _BV(PF6))) { 

// add keycode for + in the report

KeyboardReport->KeyCode[UsedKeyCodes++] = HID_KEYBOARD_SC_KEYPAD_PLUS;

}

else if(!(PINF & _BV(PF5))) { 

// add keycode for del in the report

KeyboardReport->KeyCode[UsedKeyCodes++] = HID_KEYBOARD_SC_DELETE;

}

else if(!(PINF & _BV(PF4))) { 

// add keycode for enter in the report

KeyboardReport->KeyCode[UsedKeyCodes++] = HID_KEYBOARD_SC_KEYPAD_ENTER;

}



*ReportSize = sizeof(USB_KeyboardReport_Data_t);

return false;

}


/** HID class driver callback function for the processing of HID reports from the host.

 *

 *  param[in] HIDInterfaceInfo  Pointer to the HID class interface 
configuration structure being referenced

 *  param[in] ReportID    Report ID of the received report from the host

 *  param[in] ReportType  The type of report that the host has sent,
 either HID_REPORT_ITEM_Out or HID_REPORT_ITEM_Feature

 *  param[in] ReportData  Pointer to a buffer where the received report has been stored

 *  param[in] ReportSize  Size in bytes of the received HID report

 */

void CALLBACK_HID_Device_ProcessHIDReport(USB_ClassInfo_HID_Device_t* const HIDInterfaceInfo,

                                          const uint8_t ReportID,

                                          const uint8_t ReportType,

                                          const void* ReportData,

                                          const uint16_t ReportSize)

{

uint8_t* LEDReport = (uint8_t*)ReportData;


if (*LEDReport & HID_KEYBOARD_LED_CAPSLOCK)

{ // switch on the LED for Caps Lock

PORTD |= 0x02; // make PD1 high

}

else

{ // switch off the LED

PORTD &= 0xfd; // make PD1 low

}


}

###

 

Circuit Diagrams

Circuit-Diagram-Arduino-Based-USB-Number-Keypad-

Project Datasheet

https://www.engineersgarage.com/wp-content/uploads/2019/10/Numeric-Keypard-Codes.zip

Project Video

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Filed Under: Electronic Projects

 

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