Update README files for sharp displays.

README.md

@@ -1,6 +1,6 @@
 A lightweight and minimal MicroPython GUI library for display drivers based on
-the `framebuf` class. With the exception of the Nokia 5110, such drivers are
-currently for color and monochrome OLED displays. This is coincidental.
+the `framebuf` class. Various display technologies are supported, primarily
+small color OLED's.
 
 These images don't do justice to the OLED displays which are visually
 impressive with bright colors and extreme contrast. For some reason they are
@@ -54,6 +54,9 @@ display driver is subclassed from the `framebuf` class. Examples are:
  * A driver for [Adafruit 1.5 inch OLED](https://www.adafruit.com/product/1431)
  and [Adafruit 1.27 inch OLED](https://www.adafruit.com/product/1673) may be
  found [here](./drivers/ssd1351/README.md).
+ * A driver for Sharp ultra low power consumption monochrome displays such as
+ [2.7 inch 400x240 pixels](https://www.adafruit.com/product/4694)
+ is [here](./drivers/sharp/README.md).
 
 Widgets are intended for the display of data from physical devices such as
 sensors. The GUI is display-only: there is no provision for user input. This
@@ -462,6 +465,10 @@ For a driver to support `nanogui` it must be subclassed from
 the display size in pixels. This, and a `show` method, are all that is required
 for monochrome drivers.
 
+Refresh must be handled by a `show` method taking no arguments; when called,
+the contents of the buffer underlying the `FrameBuffer` must be copied to the
+hardware.
+
 For color drivers, to conserve RAM it is suggested that 8-bit color is used
 for the `framebuf`. If the hardware does not support this, conversion to the
 supported color space needs to be done "on the fly" as per the SSD1351 driver.
@@ -476,10 +483,6 @@ form acceptable to the driver. For 8-bit rrrgggbb this can be:
 ```
 This should be amended if the hardware uses a different 8-bit format.
 
-Refresh must be handled by a `show` method taking no arguments; when called,
-the contents of the buffer underlying the `FrameBuffer` must be copied to the
-hardware.
-
 The `Writer` (monochrome) or `CWriter` (color) classes and the `nanogui` module
 should then work automatically.
 

drivers/sharp/README.md

@@ -71,7 +71,8 @@ The datasheet specifies a minimum refresh rate of 1Hz.
 
  1. `sharptest.py` Basic functionality test.
  2. `clocktest.py` Digital and analog clock display.
- 3. `clock_batt.py` As above but designed for low power operation.
+ 3. `clock_batt.py` As above but designed for low power operation. Pyboard
+ specific.
 
 `sharptest` should not be run for long periods as it does not regularly refresh
 the display. It tests `writer.py` and some `framebuffer` graphics primitives.
@@ -124,6 +125,28 @@ the 2.7 inch display this is 400*240//8 = 12000 bytes in size. This should be
 instantiated as soon as possible in the application to ensure that sufficient
 contiguous RAM is available.
 
+## 4.1 Micropower applications
+
+These comments largely assume a Pyboard host. The application should import
+`upower` from 
+[micropython-micropower](https://github.com/peterhinch/micropython-micropower).
+This turns the USB interface off if not in use to conserve power. It also
+provides an `lpdelay` function to implement a delay using `pyb.stop()` to
+conserve power.
+
+In tests the `clock_batt` demo consumed 700μA between updates. A full refresh
+every 30s consumed about 48mA for 128ms. These figures correspond to a mean
+current consumption of 904μA implying about 46 days operation per AH of
+battery capacity. LiPo cells of 2AH capacity are widely available offering a
+theoretical runtime of 92 days between charges.
+
+Lower currents might be achieved using standby but I have major doubts. This is
+because it is necessary to toggle the VCOM bit at a minimum of 1Hz. Waking from
+standby uses significan amounts of power as the modules are compiled. Even if
+frozen bytecode is used, there is still significant power usage importing
+modules and instantiating classes; this usage is not incurred in the loop in
+the demo.
+
 # 5. Resources
 
 [Schematic for 2.7" unit](https://learn.adafruit.com/assets/94077)

drivers/sharp/clock_batt.py

@@ -61,26 +61,22 @@ def aclock():
     lbldat = Label(wri, 100, 230, 100)
     hrs = Pointer(dial)
     mins = Pointer(dial)
-    secs = Pointer(dial)
 
     hstart =  0 + 0.7j  # Pointer lengths and position at top
     mstart = 0 + 0.92j
-    sstart = 0 + 0.92j 
     while True:
         t = rtc.datetime()  # (year, month, day, weekday, hours, minutes, seconds, subseconds)
-        hang = -t[4]*pi/6 - t[5]*pi/360  # Angles of hour and minute hands
+        hang = -t[4]*pi/6 - t[5]*pi/360  # Angles of hands in radians
         mang = -t[5] * pi/30
-        sang = -t[6] * pi/30
-        if abs(hang - mang) < pi/360:  # Avoid overlap of hands
-            hang += pi/18
+        if abs(hang - mang) < pi/360:  # Avoid visually confusing overlap of hands
+            hang += pi/30  # by making hr hand lag slightly
         hrs.value(hstart * uv(hang))
         mins.value(mstart * uv(mang))
-        secs.value(sstart * uv(sang))
-        lbltim.value('{:02d}.{:02d}.{:02d}'.format(t[4], t[5], t[6]))
+        lbltim.value('{:02d}.{:02d}'.format(t[4], t[5]))
         lbldat.value('{} {} {} {}'.format(days[t[3] - 1], t[2], months[t[1] - 1], t[0]))
         refresh(ssd)
-        # Power saving: only refresh every 10s
-        for _ in range(10):
+        # Power saving: only refresh every 30s
+        for _ in range(30):
             upower.lpdelay(1000)
             ssd.update()  # Toggle VCOM
 

drivers/sharp/clocktest.py

@@ -64,11 +64,14 @@ def aclock():
     sstart = 0 + 0.92j 
     while True:
         t = utime.localtime()
-        # Add 0.5min offset to hour hand. This avoids a confusing display by
-        # ensuring hour and minute hand never exactly overlap
-        hrs.value(hstart * uv(-t[3]*pi/6 - t[4]*pi/360) - pi/720)
-        mins.value(mstart * uv(-t[4] * pi/30))
-        secs.value(sstart * uv(-t[5] * pi/30))
+        hang = -t[4]*pi/6 - t[5]*pi/360  # Angles of hour and minute hands
+        mang = -t[5] * pi/30
+        sang = -t[6] * pi/30
+        if abs(hang - mang) < pi/360:  # Avoid overlap of hr and min hands
+            hang += pi/30  # which is visually confusing. Add slight lag to hts
+        hrs.value(hstart * uv(hang))
+        mins.value(mstart * uv(mang))
+        secs.value(sstart * uv(sang))
         lbltim.value('{:02d}.{:02d}.{:02d}'.format(t[3], t[4], t[5]))
         lbldat.value('{} {} {} {}'.format(days[t[6]], t[2], months[t[1] - 1], t[0]))
         refresh(ssd)