rotaryDecoder

Arduino library for a PCF8574 based rotary decoder - supports 4 RE.

Description

Experimental - not tested yet

Interface

rotaryDecoder(const int8_t address, TwoWire *wire = Wire);
bool begin(uint8_t sda, uint8_t scl, uint8_t cnt = 4) ESP32 ea initializes the class. sets I2C pins. cnt is the number of rotary encoders connected. returns true if the PCF8574 is on the I2C bus.
bool begin(uint8_t cnt = 4) UNO ea. initializes the class. cnt 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 inital state of the 4 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. These will add +1 or -1 depending on direction.
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

uint32_t getValue(uint8_r re) returns the RE counter.
void setValue(uint8_r re, uint32_t val = 0) (re)set the internal counter to val, default 0

Debugging

int8_t getLastPosition(uint8_r re)

Performance

As the decoder is based upon a PCF8574, a I2C device, the performance is affected by the clockspeed 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 (with no updates it is ~8 us faster). Note that above 500KHz the gain becomes less while reliability of signal decreases. (500KHz is ~3x faster than 100 KHz)

I2C speed	time (us)	delta	%%
100 KHz	247
200 KHz	146	99	40%
300 KHz	110	36	24%
400 KHz	95	15	14%
500 KHz	84	11	12%
600 KHz	79	5	6%
700 KHz	73	6	8%

At @400KHz it can update 4 rotary encoders in ~100us. 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..

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