Arduino library for 8x8 or smaller KeyPad connected to an I2C PCF8575.
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.
Since 0.3.0 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/I2CKeyPad. which is an 4x4 version using PCF8574.
- https://github.com/RobTillaart/PCF8575
- https://github.com/RobTillaart/AnalogKeypad
- https://github.com/RobTillaart/I2CKeyPad4x4
- https://github.com/RobTillaart/I2CKeyPad8x8
The PCF8575 is connected between the processor and the (default) 8x8 keypad. See the conceptual schema below. It might take some trying to get the correct pins connected.
PROC PCF8575 KEYPAD
+--------+ +---------+ +---------+
| | | 0 |<-------->| R |
| SDA |<------>| . |<-------->| O |
| SCL |<------>| . |<-------->| W |
| | | 7 |<-------->| S |
| | | | | |
| | | 8 |<-------->| C |
| | | . |<-------->| O |
| | | . |<-------->| L |
| | | 15 |<-------->| S |
+--------+ +---------+ +---------+
This library uses a PCF8575 chip.
| Type | Address-range | Notes |
|---|---|---|
| PCF8575 | 0x20 to 0x27 | same range as PCF8574 ! |
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 "I2CKeyPad8x8.h"- 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. Call wire.begin() first!
- bool isConnected() returns false if the PCF8575 cannot be connected to.
- uint8_t getKey() Returns default 0..63 for regular keys, Returns I2C_KEYPAD8X8_NOKEY (64) if no key is pressed and and I2C_KEYPAD8X8_FAIL (17) in case of an error, e.g. multiple keys pressed. If a debounce delay is set, it might return I2C_KEYPAD8X8_THRESHOLD if called too fast.
- uint8_t getLastKey() Returns the last valid key pressed 0..63, or I2C_KEYPAD8X8_NOKEY (64) 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.
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 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).
Experimental
Since version 0.3.0, 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_KEYPAD8x8_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_KEYPAD8x8_THRESHOLD (255).
Feedback welcome!
After the keypad.begin() the sketch calls the keyPad.getKey() to read values from the keypad.
- If no key is pressed I2C_KEYPAD8x8_NOKEY code (16) is returned.
- If the read value is not valid, e.g. two keys pressed, I2C_KEYPAD8x8_FAIL code (17) is returned.
- If a debounce threshold is set, I2C_KEYPAD8x8_THRESHOLD might be returned. See section above.
- Otherwise a number 0..63 is returned.
Note NOKEY and FAIL both 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.
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 the device over I2C. See examples.
- update documentation
- keep in sync with I2CKeyPad as much as possible.
- test extensively
- basic working (OK)
- interrupts
- keymapping
- performance
- improve error handling?
- I2C_KEYPAD_ERR_MODE
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