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# 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%   | preferred max
| 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°. (not tested)


## Operational

See examples..