GY-63_MS5611/libraries/I2CKeyPad8x8/README.md

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# I2CKeyPad8x8

Arduino library for 8x8 or smaller KeyPad connected to an I2C PCF8575.


## Description

EXPERIMENTAL (first tests ==> OK)

The I2CKeyPad8x8 library implements the reading of a 8x8 keypad by means of a PCF8575.
Smaller keypads, meaning less columns or rows (e.g. 5x4) can be read with it too.

Relates to https://github.com/RobTillaart/I2CKeyPad. which is an version using PCF8574.


## Connection

The PCF8575 is connected between the processor and the (default) 8x8 keypad.
See the conceptual schema below. 

```
          PROC             PCF8575              KEYPAD
        +--------+        +--------+          +--------+
        |        |        |       0|----------|R       |
        |    SDA |--------|       .|----------|O       |
        |    SCL |--------|       .|----------|W       |
        |        |        |       7|----------|S       |
        |        |        |       .|          |        |
        |        |        |       .|          |        |
        |        |        |       8|----------|C       |
        |        |        |       .|----------|O       |
        |        |        |       .|----------|L       |
        |        |        |      15|----------|S       |
        +--------+        +--------+          +--------+ 
```


## Interface

- **I2CKeyPad8x8(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 PCF8575 with the given address is connected properly.
- **bool begin(uint8_t sda, uint8_t scl)** for ESP32.
The return value shows if the PCF8575 with the given address is connected properly.
- **bool isConnected()** returns false if the PCF8575 cannot be connected to.
- **uint8_t getKey()** Returns default 0..63 for regular keys, 
Returns 64 if no key is pressed and 65 in case of an error.
- **uint8_t getLastKey()** Returns the last **valid** key pressed 0..63. Initially it will return 64 (NOKEY).
- **bool isPressed()** Returns true if one or more keys of the keyPad is pressed, 
however it is not checked if multiple keys are pressed.


#### KeyMap functions

**loadKeyMap()** must be called before **getChar()** and **getLastChar()**!

- **char getChar()** returns the char corresponding to mapped key pressed.
- **char getLastChar()** returns the last char pressed.
- **bool loadKeyMap(char \* keyMap)** keyMap should point to a (global) char array of length 66.
This array maps index 0..63 on a char and index \[64\] maps to **I2CKeyPad8x8_NOKEY** (typical 'N') 
and index \[65\] maps **I2CKeyPad8x8_FAIL** (typical 'F'). index 66 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.


Note: a keyMap char array may be longer than 66 characters, but only the first 66 are used.
The length is **NOT** checked upon loading (as it may contain a NULL char).


#### Basic working

After the **keypad.begin()** the sketch calls the **keyPad.getKey()** to read values from the keypad. 
- If no key is pressed **I2CKeyPad8x8_NOKEY** code (16) is returned.
- If the read value is not valid, e.g. two keys pressed, **I2CKeyPad8x8_FAIL** code (17) is returned.
- Otherwise a number 0..63 is returned.

Note NOKEY and FAIL bot have bit 8 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 PCF8575 to generate interrupts on the PCF8575 when a key is pressed. 
This makes checking the keypad far more efficient as one does not need to poll over I2C.

See examples. (TODO)


## Operation

See examples


## Future


#### must
- update documentation

#### should
- test extensively
  - basic working (OK)
  - interrupts
  - keymapping
  - performance
- keep in sync with **I2CKeyPad** as much as possible.

#### would