Arduino library for 4x4 (or smaller) keypad connected to an I2C PCF8574.
The I2CKeyPad library implements the reading of a 4x4 keypad by means of a PCF8574. Smaller keypads, meaning less columns or rows (4x3) can be read with it too.
Since 0.3.2 the library allows a 5x3, 6x2 or 8x1 or smaller keypad to be connected too.
Since 0.5.0 the library can set a debounce threshold. If this is set (> 0) the getKey() and getChar() functions can return I2C_KEYPAD_THRESHOLD (255).
Relates strongly to https://github.com/RobTillaart/I2CKeyPad8x8. which is an 8x8 version using PCF8575.
The PCF8574 is connected between the processor and the (default) 4x4 keypad. See the conceptual schema below. It might take some trying to get the correct pins connected.
PROC PCF8574 KEYPAD
+--------+ +---------+ +---------+
| | | 0 |<-------->| R |
| SDA |<------>| 1 |<-------->| O |
| SCL |------->| 2 |<-------->| W |
| | | 3 |<-------->| S |
| | | | | |
| | | 4 |<-------->| C |
| | | 5 |<-------->| O |
| | | 6 |<-------->| L |
| | | 7 |<-------->| S |
+--------+ +---------+ +---------+
This library uses a PCF8574 or a PCF8574A chip. These devices are identical in behaviour although there are two distinct address ranges.
Type | Address-range | Notes |
---|---|---|
PCF8574 | 0x20 to 0x27 | same range as PCF8575 ! |
PCF8574A | 0x38 to 0x3F |
Be careful to select an unique I2C address for every device on the bus.
Sometimes you need to control more devices than possible with the default address range the device provides. This is possible with an I2C multiplexer e.g. TCA9548 which creates up to eight channels (think of it as I2C subnets) which can use the complete address range of the device.
Drawback of using a multiplexer is that it takes more administration in your code e.g. which device is on which channel. This will slow down the access, which must be taken into account when deciding which devices are on which channel. Also note that switching between channels will slow down other devices too if they are behind the multiplexer.
#include "I2CKeyPad.h"
Experimental
Supported modi
There are 4 modi supported, and every mode will also support smaller keypads. E.g. a 4x3 keypad can be read in mode 4x4 or in mode 5x3.
modi | value | definition | notes |
---|---|---|---|
4x4 | 44 | I2C_KEYPAD_4x4 | default, also for 4x3 4x2 4x1 3x3 3x2 3x1 etc. |
5x3 | 53 | I2C_KEYPAD_5x3 | also for 5x2 or 5x1 etc. |
6x2 | 62 | I2C_KEYPAD_6x2 | also for 6x1 etc. |
8x1 | 81 | I2C_KEYPAD_8x1 | not real matrix, connect pins to switch to GND. |
Note: loadKeyMap() must be called before getChar() and getLastChar()!
WARNING
If there is no key map loaded the user should NOT call getChar() or getLastChar() as these would return meaningless bytes.
char normal_keymap[19] = "123A456B789C*0#DNF"; // typical normal key map (phone layout)
char repeat_keymap[19] = "1234123412341234NF"; // effectively 4 identical columns
char partial_keymap[19] = "1234 NF"; // top row
char diag_keymap[19] = "1 2 3 4NF"; // diagonal keys only
In the examples above a 'space' key might be just meant to ignore. However functionality there is no limit how one wants to use the key mapping. It is even possible to change the mapping runtime after each key.
Note: a keyMap char array may be longer than 18 characters, but only the first 18 are used. The length is NOT checked upon loading.
Note: The 5x3, 6x2 and the 8x1 modi also uses a key map of length 18.
Experimental
Since version 0.5.0, the library implements an experimental debounce threshold which is non-blocking.
If a key bounces, it can trigger multiple interrupts, while the purpose is to act like only one keypress. The debounce threshold results in a fast return of getKey() (with I2C_KEYPAD_THRESHOLD) if called too fast.
The default value of the debounce threshold is zero to be backwards compatible. The value is set in milliseconds, with a maximum of 65535 ==> about 65 seconds or 1 minute. A value of 1 still allows ~1000 getKey() calls per second (in theory). A value of 65535 can be used e.g. for a delay after entering a wrong key code / password. Setting a high value might result in missed keypresses so use with care.
The default value of the debounce threshold is zero to be backwards compatible.
If a debounce threshold is set, and getKey() or getChar() is called too fast, these functions will return I2C_KEYPAD_THRESHOLD (255).
Feedback welcome!
After the keypad.begin() the sketch calls the keyPad.getKey() to read values from the keypad.
Note NOKEY and FAIL both have bit 4 set, all valid keys don't. This allows fast checking for valid keys.
Only if a key map is loaded, the user can call getChar() and getLastChar() to get mapped keys.
The library enables the PCF8574 to generate interrupts on the PCF8574 when a key is pressed. This makes checking the keypad far more efficient as one does not need to poll the device over I2C. See examples.
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