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Encoders: add to algorithm notes.

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Peter Hinch 2022-04-06 17:55:34 +01:00
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encoders/ENCODERS.md
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@ -31,7 +31,7 @@ latency or input pulse rates.
# 2. Basic encoder script # 2. Basic encoder script
This comes from `encoder_portable.py` in this repo. It uses the simplest and This comes from `encoder_portable.py` in this repo. It uses the simplest and
fastest algorithm I know. It should run on any MicrPython platform, but please fastest algorithm I know. It should run on any MicroPython platform, but please
read the following notes as there are potential issues. read the following notes as there are potential issues.
```python ```python
@ -40,7 +40,6 @@ from machine import Pin
class Encoder: class Encoder:
def __init__(self, pin_x, pin_y, scale=1): def __init__(self, pin_x, pin_y, scale=1):
self.scale = scale self.scale = scale
self.forward = True
self.pin_x = pin_x self.pin_x = pin_x
self.pin_y = pin_y self.pin_y = pin_y
self._pos = 0 self._pos = 0
@ -51,13 +50,13 @@ class Encoder:
self.x_interrupt = pin_x.irq(trigger=Pin.IRQ_RISING | Pin.IRQ_FALLING, handler=self.x_callback) self.x_interrupt = pin_x.irq(trigger=Pin.IRQ_RISING | Pin.IRQ_FALLING, handler=self.x_callback)
self.y_interrupt = pin_y.irq(trigger=Pin.IRQ_RISING | Pin.IRQ_FALLING, handler=self.y_callback) self.y_interrupt = pin_y.irq(trigger=Pin.IRQ_RISING | Pin.IRQ_FALLING, handler=self.y_callback)
def x_callback(self, pin): def x_callback(self, pin_x):
self.forward = pin() ^ self.pin_y() forward = pin_x() ^ self.pin_y()
self._pos += 1 if self.forward else -1 self._pos += 1 if forward else -1
def y_callback(self, pin): def y_callback(self, pin_y):
self.forward = self.pin_x() ^ pin() ^ 1 forward = self.pin_x() ^ pin_y() ^ 1
self._pos += 1 if self.forward else -1 self._pos += 1 if forward else -1
def position(self, value=None): def position(self, value=None):
if value is not None: if value is not None:
@ -178,7 +177,7 @@ are shown in this state diagram.
![Image](./state_diagram.png) ![Image](./state_diagram.png)
The truth table includes the previous (`xp` and `yp`) and current (`x` and `y`) The truth table includes the previous (`xp` and `yp`) and current (`x` and `y`)
values of the signals. It includes all logically possible cobinations of these values of the signals. It includes all logically possible combinations of these
signals. These include cases where no change occurs (marked `n`) and cases signals. These include cases where no change occurs (marked `n`) and cases
which are physically impossible (`x`). The latter arise because both signals which are physically impossible (`x`). The latter arise because both signals
cannot change state simultaneously. cannot change state simultaneously.
@ -223,7 +222,7 @@ the edge occurs and consequently varies in real time. Another ISR may be
running. Higher priority interrupts may be pending service. In the case of soft running. Higher priority interrupts may be pending service. In the case of soft
IRQ's garbage collection may be in progress. IRQ's garbage collection may be in progress.
Consider the fllowing ISR: Consider the following ISR:
```python ```python
def x_callback(self, pin_x): def x_callback(self, pin_x):
forward = pin_x() ^ self.pin_y() forward = pin_x() ^ self.pin_y()