encode strings / chars as ascii before sending to the printer

adafruit_thermal_printer/thermal_printer.py

@@ -202,7 +202,7 @@ def _write_char(self, char):
         if char == '\r':
             return  # Strip carriage returns by skipping them.
         self._wait_timeout()
-        self._uart.write(char)
+        self._uart.write(char.encode('ascii'))
         delay = self._byte_delay_s
         # Add extra delay for newlines or moving past the last column.
         if char == '\n' or self._column == self._max_column:
@@ -238,7 +238,7 @@ def _unset_print_mode(self, mask):
 
     def send_command(self, command):
         """Send a command string to the printer."""
-        self._uart.write(command)
+        self._uart.write(command.encode('ascii'))
 
     # Do initialization in warm_up instead of the initializer because this
     # initialization takes a long time (5 seconds) and shouldn't happen during

examples/thermal_printer_simpletest.py

@@ -5,7 +5,6 @@
 
 import adafruit_thermal_printer
 
-
 # Pick which version thermal printer class to use depending on the version of
 # your printer.  Hold the button on the printer as it's powered on and it will
 # print a test page that displays the firmware version, like 2.64, 2.68, etc.
@@ -25,6 +24,10 @@
 # during power-up and it will show the baud rate).  Most printers use 19200.
 uart = busio.UART(TX, RX, baudrate=19200)
 
+# For a computer, use the pyserial library for uart access.
+# import serial
+# uart = serial.Serial("/dev/serial0", baudrate=19200, timeout=3000)
+
 # Create the printer instance.
 printer = ThermalPrinter(uart, auto_warm_up=False)