add SD card example for Inky Frame

micropython/examples/inky_frame/README.md

@@ -10,6 +10,7 @@
   - [PlaceKitten](#placekitten)
   - [Quote of the Day](#quote-of-the-day)
   - [Random Joke](#random-joke)
+  - [SD Card Test](#sd-card-test)
   - [XKCD Daily](#xkcd-daily)
 
 ## PicoGraphics
@@ -30,7 +31,9 @@ Finally for examples loading images, you'll need `sdcard.mpy` from `common/lib`.
 ### Button Test
 [button_test.py](button_test.py)
 
-This example shows you a simple, non-interrupt way of reading Inky Frame's buttons with a loop that checks to see if buttons are pressed.
+Inky Frame's buttons (and the RTC alarm, busy signal from the screen and external trigger from the hack header) are connected to a shift register to help conserve pins, and to allow these inputs to wake the board up from sleep.
+
+This example demonstrates a simple way of reading when a button has been pushed by reading the shift register and checking if the bit in a specific position is 0 or 1.
 
 ### Daily Activity
 [inky_frame_daily_activity.py](inky_frame_daily_activity.py)
@@ -38,7 +41,7 @@ This example shows you a simple, non-interrupt way of reading Inky Frame's butto
 Generate a random activity from Bored API.
 
 ### Image Gallery
-[/image_gallery](/image_gallery)
+[/image_gallery](../inky_frame/image_gallery)
 
 This photo frame example displays local images on Inky Frame and lets you switch between them with the buttons. Use `image_gallery.py` if your images are stored on your Pico, or `image_gallery_sd.py` if the images are on your SD card.
 
@@ -74,6 +77,11 @@ Jokes are rendered into images "offline" by our feed2image service for two reaso
 
 For bugs/contributions or to complain about a joke, see: https://github.com/pimoroni/feed2image
 
+### SD Card Test
+[sd_test.py](sd_test.py)
+
+This simple example shows how to read and write from the SD card on Inky Frame.
+
 ### XKCD Daily
 [inky_frame_xkcd_daily.py](inky_frame_xkcd_daily.py)
 

micropython/examples/inky_frame/sd_test.py

@@ -0,0 +1,26 @@
+# This simple example shows how to read and write from the SD card on Inky Frame.
+from machine import Pin, SPI
+import sdcard
+import os
+
+# set up the SD card
+sd_spi = SPI(0, sck=Pin(18, Pin.OUT), mosi=Pin(19, Pin.OUT), miso=Pin(16, Pin.OUT))
+sd = sdcard.SDCard(sd_spi, Pin(22))
+os.mount(sd, "/sd")
+
+# create a file and add some text
+# if this file already exists it will be overwritten
+with open("/sd/inkytest.txt", "w") as f:
+    f.write("Hello Inky!\r\n")
+    f.close()
+
+# open the file and append some text (useful for logging!)
+with open("/sd/inkytest.txt", "a") as f:
+    f.write("We're appending some text\r\n")
+    f.close()
+
+# read the file and print the contents to the console
+with open("/sd/inkytest.txt", "r") as f:
+    data = f.read()
+    print(data)
+    f.close()