6.2 KiB
rotaryDecoderSwitch
Arduino library for a PCF8574 based rotary decoder - supports 2 rotary encoders with a switch.
Description
This experimental library uses a PCF8574 to read the pulses of a rotary encoder. As a PCF8574 has 8 lines up to 2 decoders with a switch can be read over I2C. The PCF interrupt line can be used to detect changes in the position of the encoders or if a switch is pressed.
If only 1 rotary encoders is connected one should use the lower bit lines as the library assumes these are used. Furthermore it is advised to connect the free PCF8574 pins to GND so you will not get unintended interrupts.
Strongly related to https://github.com/RobTillaart/rotaryDecoder
The interface is kept the same as much as possible.
// connect up to 2 rotary encoders with a switch to 1 PCF8574.
//
// RotaryEncoder PCF8574 UNO REMARKS
// -----------------------------------------------------------
// 1 pin A pin 0
// 1 pin B pin 1
// 1 switch pin 2 (switch to gnd)
// pin 3 (reserved)
// 2 pin A pin 4
// 2 pin B pin 5
// 2 switch pin 6 (switch to gnd)
// pin 7 (reserved)
//
// SDA A4
// SCL A5
//
Note the above mapping is sort of compatible to using the rotaryDecoder class and using device 0 and 2 only,
Related
Interface
#include "rotaryDecoderSwitch.h"
Constructor
- rotaryDecoderSwitch(const int8_t address, TwoWire *wire = Wire); constructor to set the address and optional the Wire bus.
- bool begin(uint8_t count = 2) UNO ea. initializes the class. count is the number of rotary encoders connected. returns true if the PCF8574 is on the I2C bus.
- bool isConnected() returns true if the PCF8574 is on the I2C bus.
Core functions
- void readInitialState() read the initial state of the 2 rotary encoders. Typically called in setup only, or after a sleep e.g. in combination with setValue()
- bool checkChange() polling to see if one or more RE have changed, without updating the counters.
- void update() update the internal counters of the RE, and the flags if a key is pressed. The counters will add +1 or -1 depending on direction. Need to be called before getValue() or before getKeyPressed(). Note that update() must be called as soon as possible after the interrupt occurs (or as often as possible when polling).
- void updateSingle() update the internal counters of the RE. This will add +1 +2 or +3 as it assumes that the rotary encoder only goes into a single direction.
Counters & keypresses
- uint32_t getValue(uint8_r re) returns the RE counter. (re = 0 or 1).
- void setValue(uint8_r re, uint32_t val = 0) (re)set the internal counter to val, default 0
- bool isKeyPressed(uint8_t re) returns true is the switch is pressed of the RE selected (re = 0 or 1). Note one needs to call update() first!
Debugging
- int8_t getLastPosition(uint8_r re) (re = 0 or 1). returns last position.
- int8_t getRaw()
Performance
As the decoder is based upon a PCF8574, a I2C device, the performance is affected by the clock speed of the I2C bus. All four core functions have one call to _read() which is the most expensive part.
Early tests gave the following indicative times (Arduino UNO) for the update() function. Note that above 500KHz the gain becomes less while reliability of signal decreases. (500KHz is ~3x faster than 100 KHz) As 400 KHz is a standard I2C clock speed it is the preferred one.
| I2C speed | time (us) | delta | %% | Notes |
|---|---|---|---|---|
| 100 KHz | 234 | |||
| 200 KHz | 136 | 98 | 42% | |
| 300 KHz | 100 | 36 | 26% | |
| 400 KHz | 85 | 15 | 15% | preferred max |
| 500 KHz | 78 | 7 | 8% | |
| 600 KHz | 67 | 11 | 14% | (strange outlier) |
| 700 KHz | 63 | 4 | 6% |
(test results differ slightly from the rotaryEncoder class)
At @400KHz it can update 2 rotary encoders in less than 90 us. At a 50% update percentage this implies a max of about 5000 update() calls per second in theory. to be tested in practice
Note that a high speed drill goes up to 30000 RPM = 500 RPS = 2000 interrupts per second, assuming 4 pulses == 360<36>. (not tested)
Operational
See examples..
Future
Must
- update documentation
- add schema
- keep in sync with rotaryDecoder library
Should
- think of what to do with the two "idle lines"
Could
Wont
Support
If you appreciate my libraries, you can support the development and maintenance. Improve the quality of the libraries by providing issues and Pull Requests, or donate through PayPal or GitHub sponsors.
Thank you,