Arduino library for a PCF8574 based rotary decoder - supports 4 rotary encoders.
This experimental library uses a PCF8574 to read the pulses of a rotary encoder. As a PCF8574 has 8 lines up to 4 decoders can be read over I2C. The PCF interrupt line can be used to detect changes in the position of the encoders.
If less than 4 rotary encoders are 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.
#include "rotaryEncoder.h"- rotaryDecoder(const int8_t address, TwoWire *wire = Wire);
- bool begin(uint8_t count = 4) UNO ea. initializes the class. count is the number of rotary encoders connected. (Max 4 per PCF8574) Returns true if the PCF8574 is on the I2C bus.
- bool isConnected() returns true if the PCF8574 is on the I2C bus.
- void readInitialState() read the initial 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 internal counters.
- void update() update the internal counters of the RE. The counters will add +1 or -1 depending on rotation 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.
- uint32_t getValue(uint8_r re) returns the RE counter.
- void setValue(uint8_r re, uint32_t value = 0) (re)set the internal counter to value, default 0
Warning the write1(pin, value) might alter the state of the rotary encoder pins. So this functionality should be tested thoroughly for your application. Especially the write() is experimental, see issue #10, feedback welcome.
Read1() and write1() are functions to access the pins of the PCF8574 that are not used for rotary encoders. The user must guard that especially writing the pins do not interfere with the rotary encoder pins.
- uint8_t read1(uint8_t pin) reads a single pin (0..7). Returns HIGH or LOW.
- bool write1(uint8_t pin, uint8_t value) writes a single pin (0..7). Value should be LOW (0) or HIGH (other values).
- uint8_t read8() read all pins in one I2C IO action. When one need to access multiple input pins this is faster but need some bit masking.
- bool write8(uint8_t value) writes to multiple pins at once, e.g. to control multiple LEDs in one IO action. As said before the user must guard not to interfere with the rotary encoder pins.
- int8_t getLastPosition(uint8_r re) Returns last position.
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 \read8() 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 500 KHz the gain becomes less while reliability of signal decreases. (500 KHz is about 3x faster than 100 KHz in practice.) As 400 KHz is a standard I2C clock speed it is the preferred one.
| I2C speed | time (us) | delta | %% | Notes |
|---|---|---|---|---|
| 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 400 KHz 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)
- update documentation
- picture how to connect e.g two rotary encoders which pins to used
- test with a high speed drill like a Dremel-tool.
- invert flag to adjust to RE that give their pulse just the other way around?
- setInvert(bool); getInvert();
- per channel / all?
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