Create code.py for new guide

Example of accessing the Tiny Code Reader from Useful Sensors on a Trinkey using CircuitPython. Pete Warden

Reading_QR_Codes/code.py

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+# SPDX-FileCopyrightText: 2023 Pete Warden
+# SPDX-License-Identifier: Apache-2.0
+#
+# Example of accessing the Tiny Code Reader from Useful Sensors on a Trinkey
+# using CircuitPython. See https://usfl.ink/tcr_dev for the full developer guide.
+
+import board
+import busio
+import struct
+import time
+import usb_hid
+
+from adafruit_hid.keyboard import Keyboard
+from adafruit_hid.keyboard_layout_us import KeyboardLayoutUS
+
+# The code reader has the I2C ID of hex 0c, or decimal 12.
+TINY_CODE_READER_I2C_ADDRESS = 0x0C
+
+# How long to pause between sensor polls.
+TINY_CODE_READER_DELAY = 0.2
+
+TINY_CODE_READER_LENGTH_OFFSET = 0
+TINY_CODE_READER_LENGTH_FORMAT = "H"
+TINY_CODE_READER_MESSAGE_OFFSET = TINY_CODE_READER_LENGTH_OFFSET + struct.calcsize(TINY_CODE_READER_LENGTH_FORMAT)
+TINY_CODE_READER_MESSAGE_SIZE = 254
+TINY_CODE_READER_MESSAGE_FORMAT = "B" * TINY_CODE_READER_MESSAGE_SIZE
+TINY_CODE_READER_I2C_FORMAT = TINY_CODE_READER_LENGTH_FORMAT + TINY_CODE_READER_MESSAGE_FORMAT
+TINY_CODE_READER_I2C_BYTE_COUNT = struct.calcsize(TINY_CODE_READER_I2C_FORMAT)
+
+i2c = board.I2C()
+
+# Wait until we can access the bus.
+while not i2c.try_lock():
+    pass
+
+# For debugging purposes print out the peripheral addresses on the I2C bus.
+# 98 (0x62 in hex) is the address of our person sensor, and should be
+# present in the list. Uncomment the following three lines if you want to see
+# what I2C addresses are found.
+# while True:
+#    print(i2c.scan())
+#    time.sleep(TINY_CODE_READER_DELAY)
+
+# Create a keyboard device so we can send the screen lock command.
+keyboard = Keyboard(usb_hid.devices)
+layout = KeyboardLayoutUS(keyboard)
+
+last_message_string = None
+last_code_time = 0.0
+
+while True:
+    read_data = bytearray(TINY_CODE_READER_I2C_BYTE_COUNT)
+    i2c.readfrom_into(TINY_CODE_READER_I2C_ADDRESS, read_data)
+
+    message_length,  = struct.unpack_from(TINY_CODE_READER_LENGTH_FORMAT, read_data, TINY_CODE_READER_LENGTH_OFFSET)
+    message_bytes = struct.unpack_from(TINY_CODE_READER_MESSAGE_FORMAT, read_data, TINY_CODE_READER_MESSAGE_OFFSET)
+
+    if message_length > 0:
+        message_string = bytearray(message_bytes)[0:message_length].decode("utf-8")
+        is_same = (message_string == last_message_string)
+        last_message_string = message_string
+        current_time = time.monotonic()
+        time_since_last_code = current_time - last_code_time
+        last_code_time = current_time
+        # Debounce the input by making sure there's been a gap in time since we
+        # last saw this code.
+        if (not is_same) or (time_since_last_code > 1.0):
+            print(message_string)
+            try:
+                layout.write(message_string)
+            except ValueError as e:
+                pass
+            layout.write("\n")