I2CKeyPad

Arduino library for 4x4 (or smaller) keypad connected to an I2C PCF8574.

Description

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.

Breaking change

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).

Related

Relates strongly to https://github.com/RobTillaart/I2CKeyPad8x8. which is an 8x8 version using PCF8575.

• https://github.com/RobTillaart/PCF8574
• https://github.com/RobTillaart/AnalogKeypad
• https://github.com/RobTillaart/I2CKeyPad4x4
• https://github.com/RobTillaart/I2CKeyPad8x8
• https://github.com/WK-Software56/AdvKeyPad (derived work with keyboard alike interface)

Connection

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       |
        +--------+        +---------+          +---------+ 

I2C

I2C addresses

This library uses a PCF8574 or a PCF8574A chip. These devices are identical in behaviour although there are two distinct address ranges.

Be careful to select an unique I2C address for every device on the bus.

I2C multiplexing

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.

• https://github.com/RobTillaart/TCA9548

Interface

#include "I2CKeyPad.h"

Base

• I2CKeyPad(const uint8_t deviceAddress, TwoWire *wire = &Wire) The constructor sets the device address and optionally allows to selects the I2C bus to use.
• bool begin() The return value shows if the PCF8574 with the given address is connected properly. Call wire.begin() first!
• bool isConnected() returns false if the PCF8574 cannot be connected to.
• uint8_t getKey() Returns default 0..15 for regular keys, Returns I2C_KEYPAD_NOKEY (16) if no key is pressed and I2C_KEYPAD_FAIL (17) in case of an error, e.g. multiple keys pressed. If a debounce delay is set, it might return I2C_KEYPAD_THRESHOLD if called too fast.
• uint8_t getLastKey() Returns the last valid key pressed 0..15, or I2C_KEYPAD_NOKEY (16) which is also the initial value.
• bool isPressed() Returns true if one or more keys of the keyPad are pressed, however there is no check if multiple keys are pressed.

Mode functions

Experimental

• void setKeyPadMode(uint8_t mode = I2C_KEYPAD_4x4) sets the mode, default 4x4. This mode can also be used for 4x3 or 4x2 or 3x3 etc. Invalid values for mode are mapped to 4x4.
• uint8_t getKeyPadMode() returns the current mode.

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.

KeyMap functions

Note: loadKeyMap() must be called before getChar() and getLastChar()!

• char getChar() returns the char corresponding to mapped key pressed. It returns I2C_KEYPAD_THRESHOLD if called too fast.
• char getLastChar() returns the last char pressed. This function is not affected by the debounce threshold.
• bool loadKeyMap(char * keyMap) keyMap should point to a (global) char array of length 19. This array maps index 0..15 on a char and index [16] maps to I2CKEYPAD_NOKEY (typical 'N') and index [17] maps I2CKEYPAD_FAIL (typical 'F'). index 18 is the null char.

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.

Debouncing threshold

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.

• void setDebounceThreshold(uint16_t value = 0) set the debounce threshold, value in milliseconds, max 65535. The default value is zero, to reset its value.
• uint16_t getDebounceThreshold() returns the set debounce threshold.
• uint32_t getLastTimeRead() returns the time stamp of the last valid read key (or NOKEY). This variable is used for the debounce, and may be used for other purposes too. E.g. track time between keypresses.

If a debounce threshold is set, and getKey() or getChar() is called too fast, these functions will return I2C_KEYPAD_THRESHOLD (255).

Feedback welcome!

Basic working

After the keypad.begin() the sketch calls the keyPad.getKey() to read values from the keypad.

• If no key is pressed I2C_KEYPAD_NOKEY code (16) is returned.
• If the read value is not valid, e.g. two keys pressed, I2C_KEYPAD_FAIL code (17) is returned.
• If a debounce threshold is set, I2C_KEYPAD_THRESHOLD might be returned. See section above.
• Otherwise a number 0..15 is returned.

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.

Interrupts

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.

Future

Must

• update documentation

Should

• test extensively
  • basic working (OK)
  • interrupts
  • keymapping
  • performance
• improve error handling?
  • I2C_KEYPAD_ERR_MODE

Could

Wont

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Thank you,