A USB HID Keypad for the Pico RP2040 using TinyUSB and the C/C++ SDK.
This project adapts the standard hid_composite example from TinyUSB to create a 12-key (0-9, ESC, ENTER) keypad using an efficient 4x3 button matrix. This approach reads 12 buttons using only 7 GPIO pins.
The keypad logic is defined in key_matrix.h. The project reads a 4x3 matrix of buttons and translates them into standard USB HID keypresses.
The keypad uses 4 pins for rows and 3 pins for columns.
- Rows (Outputs):
GP12,GP11,GP10,GP9 - Columns (Inputs):
GP15,GP14,GP13
Some keypads may also use:
- Rows (Outputs):
GP14,GP9,GP10,GP12 - Columns (Inputs):
GP13,GP15,GP11
The key mapping is defined in a 2D array inside key_matrix.h and corresponds to the physical layout below:
| GP15 (Col 0) | GP14 (Col 1) | GP13 (Col 2) | |
|---|---|---|---|
| GP12 (Row 0) | 1 | 2 | 3 |
| GP11 (Row 1) | 4 | 5 | 6 |
| GP10 (Row 2) | 7 | 8 | 9 |
| GP9 (Row 3) | ESC | 0 | ENTER |
or:
| GP13 (Col 0) | GP15 (Col 1) | GP11 (Col 2) | |
|---|---|---|---|
| GP14 (Row 0) | 1 | 2 | 3 |
| GP9 (Row 1) | 4 | 5 | 6 |
| GP10 (Row 2) | 7 | 8 | 9 |
| GP12 (Row 3) | ESC | 0 | ENTER |
The input pins for the matrix are configured differently from a simple button-to-ground setup. The rows act as outputs, and the columns act as inputs with internal pull-down resistors.
- Row Pins (GP12-GP9): Configured as outputs.
- Column Pins (GP15-GP13): Configured as inputs with internal pull-downs, meaning they read
LOW(0) by default.
When a button is pressed, it creates a connection between its corresponding row and column pin. The scanning code works by setting one row HIGH at a time and then reading the column pins. If a column pin also reads HIGH, the firmware knows that the button at that intersection is pressed.
PICO
|
+---------+---------+
| |
Row Pin o----+----[Button]----+----o Column Pin
(Output) | | (Input w/ Pull-Down)
The pins are polled once every 10ms.
The HID keycodes are defined in pico-sdk/lib/tinyusb/src/class/hid/hid.h. This list is a useful reference for customizing the key map.
//--------------------------------------------------------------------+
// HID KEYCODE
//--------------------------------------------------------------------+
#define HID_KEY_NONE 0x00
#define HID_KEY_A 0x04
#define HID_KEY_B 0x05
#define HID_KEY_C 0x06
#define HID_KEY_D 0x07
#define HID_KEY_E 0x08
#define HID_KEY_F 0x09
#define HID_KEY_G 0x0A
#define HID_KEY_H 0x0B
#define HID_KEY_I 0x0C
#define HID_KEY_J 0x0D
#define HID_KEY_K 0x0E
#define HID_KEY_L 0x0F
#define HID_KEY_M 0x10
#define HID_KEY_N 0x11
#define HID_KEY_O 0x12
#define HID_KEY_P 0x13
#define HID_KEY_Q 0x14
#define HID_KEY_R 0x15
#define HID_KEY_S 0x16
#define HID_KEY_T 0x17
#define HID_KEY_U 0x18
#define HID_KEY_V 0x19
#define HID_KEY_W 0x1A
#define HID_KEY_X 0x1B
#define HID_KEY_Y 0x1C
#define HID_KEY_Z 0x1D
#define HID_KEY_1 0x1E
#define HID_KEY_2 0x1F
#define HID_KEY_3 0x20
#define HID_KEY_4 0x21
#define HID_KEY_5 0x22
#define HID_KEY_6 0x23
#define HID_KEY_7 0x24
#define HID_KEY_8 0x25
#define HID_KEY_9 0x26
#define HID_KEY_0 0x27
#define HID_KEY_ENTER 0x28
#define HID_KEY_ESCAPE 0x29
#define HID_KEY_BACKSPACE 0x2A
#define HID_KEY_TAB 0x2B
#define HID_KEY_SPACE 0x2C
#define HID_KEY_MINUS 0x2D
#define HID_KEY_EQUAL 0x2E
#define HID_KEY_BRACKET_LEFT 0x2F
#define HID_KEY_BRACKET_RIGHT 0x30
#define HID_KEY_BACKSLASH 0x31
#define HID_KEY_EUROPE_1 0x32
#define HID_KEY_SEMICOLON 0x33
#define HID_KEY_APOSTROPHE 0x34
#define HID_KEY_GRAVE 0x35
#define HID_KEY_COMMA 0x36
#define HID_KEY_PERIOD 0x37
#define HID_KEY_SLASH 0x38
#define HID_KEY_CAPS_LOCK 0x39
#define HID_KEY_F1 0x3A
#define HID_KEY_F2 0x3B
#define HID_KEY_F3 0x3C
#define HID_KEY_F4 0x3D
#define HID_KEY_F5 0x3E
#define HID_KEY_F6 0x3F
#define HID_KEY_F7 0x40
#define HID_KEY_F8 0x41
#define HID_KEY_F9 0x42
#define HID_KEY_F10 0x43
#define HID_KEY_F11 0x44
#define HID_KEY_F12 0x45
#define HID_KEY_PRINT_SCREEN 0x46
#define HID_KEY_SCROLL_LOCK 0x47
#define HID_KEY_PAUSE 0x48
#define HID_KEY_INSERT 0x49
#define HID_KEY_HOME 0x4A
#define HID_KEY_PAGE_UP 0x4B
#define HID_KEY_DELETE 0x4C
#define HID_KEY_END 0x4D
#define HID_KEY_PAGE_DOWN 0x4E
#define HID_KEY_ARROW_RIGHT 0x4F
#define HID_KEY_ARROW_LEFT 0x50
#define HID_KEY_ARROW_DOWN 0x51
#define HID_KEY_ARROW_UP 0x52
#define HID_KEY_NUM_LOCK 0x53
#define HID_KEY_KEYPAD_DIVIDE 0x54
#define HID_KEY_KEYPAD_MULTIPLY 0x55
#define HID_KEY_KEYPAD_SUBTRACT 0x56
#define HID_KEY_KEYPAD_ADD 0x57
#define HID_KEY_KEYPAD_ENTER 0x58
#define HID_KEY_KEYPAD_1 0x59
#define HID_KEY_KEYPAD_2 0x5A
#define HID_KEY_KEYPAD_3 0x5B
#define HID_KEY_KEYPAD_4 0x5C
#define HID_KEY_KEYPAD_5 0x5D
#define HID_KEY_KEYPAD_6 0x5E
#define HID_KEY_KEYPAD_7 0x5F
#define HID_KEY_KEYPAD_8 0x60
#define HID_KEY_KEYPAD_9 0x61
#define HID_KEY_KEYPAD_0 0x62
#define HID_KEY_KEYPAD_DECIMAL 0x63
#define HID_KEY_EUROPE_2 0x64
#define HID_KEY_APPLICATION 0x65
#define HID_KEY_POWER 0x66
#define HID_KEY_KEYPAD_EQUAL 0x67
#define HID_KEY_F13 0x68
#define HID_KEY_F14 0x69
#define HID_KEY_F15 0x6A
#define HID_KEY_F16 0x6B
#define HID_KEY_F17 0x6C
#define HID_KEY_F18 0x6D
#define HID_KEY_F19 0x6E
#define HID_KEY_F20 0x6F
#define HID_KEY_F21 0x70
#define HID_KEY_F22 0x71
#define HID_KEY_F23 0x72
#define HID_KEY_F24 0x73
#define HID_KEY_CONTROL_LEFT 0xE0
#define HID_KEY_SHIFT_LEFT 0xE1
#define HID_KEY_ALT_LEFT 0xE2
#define HID_KEY_GUI_LEFT 0xE3
#define HID_KEY_CONTROL_RIGHT 0xE4
#define HID_KEY_SHIFT_RIGHT 0xE5
#define HID_KEY_ALT_RIGHT 0xE6
#define HID_KEY_GUI_RIGHT 0xE7