diff --git a/examples/cmd.py b/examples/cmd.py
new file mode 100755
index 0000000..317cee0
--- /dev/null
+++ b/examples/cmd.py
@@ -0,0 +1,50 @@
+#!/usr/bin/env python3
+import time
+import sys
+
+from pa1010d import PA1010D
+
+
+"""
+Run raw commands against the PA1010D GPS and return the respones.
+
+Eg:
+    PMTK605 = Query Firmware Release Info
+    PMTK430 = Query Datum
+    PMTK414 = Query NMEA Output Frequency
+    PMTK400 = Query Update Rate
+    PMTK225,<1 or 0> = Enable/Disable PPS
+"""
+
+def timeout(err=None, timeout=5.0):
+    if err is None:
+        err = "Timed out!"
+    t_start = time.time()
+    while time.time() - t_start < timeout:
+        yield
+    raise TimeoutError(err)
+
+
+responses = {
+}
+
+if len(sys.argv) < 2:
+    print(f"Usage: {sys.argv[0]} <command>")
+    sys.exit()
+
+command = sys.argv[1]
+response = responses.get(command, f"$PMTK{int(command[4:]) + 100}")
+
+gps = PA1010D()
+
+gps.update()
+
+gps.send_command(sys.argv[1])
+
+if response:
+    print(f"Waiting for {response}...")
+    for t in timeout("Timed out waiting for command response."):
+        message = gps.read_sentence()
+        if message.startswith(response):
+            print(message)
+            break
diff --git a/examples/pps.py b/examples/pps.py
new file mode 100755
index 0000000..53f586b
--- /dev/null
+++ b/examples/pps.py
@@ -0,0 +1,21 @@
+#!/usr/bin/env python3
+import time
+import sys
+
+from pa1010d import PA1010D
+
+
+if len(sys.argv) < 2:
+    print(f"Usage: {sys.argv[0]} <on/off>")
+    sys.exit()
+
+gps = PA1010D()
+
+if sys.argv[1] == "on":
+    gps.send_command("PMTK255,1")
+else:
+    gps.send_command("PMTK255,0")
+
+result = gps.update()
+
+print("OK" if result else "Uh oh!")
diff --git a/library/pa1010d/__init__.py b/library/pa1010d/__init__.py
index ed75844..b41e7a3 100644
--- a/library/pa1010d/__init__.py
+++ b/library/pa1010d/__init__.py
@@ -67,7 +67,7 @@ def _write_sentence(self, bytestring):
 
         """
         for char_index in bytestring:
-            self._i2c.write_byte(self._i2c_addr, ord(char_index))
+            self._i2c.write_byte(self._i2c_addr, char_index)
 
     def send_command(self, command, add_checksum=True):
         """Send a command string to the PA1010D.
@@ -75,10 +75,13 @@ def send_command(self, command, add_checksum=True):
         If add_checksum is True (the default) a NMEA checksum will automatically be computed and added.
 
         """
+        if type(command) is not bytes:
+            command = command.encode("ascii")
+
         # TODO replace with pynmea2 functionality
-        if command.startswith("$"):
+        if command[0] == b"$":
             command = command[1:]
-        if command.endswith("*"):
+        if command[-1] == b"*":
             command = command[:-1]
 
         buf = bytearray()
@@ -112,7 +115,7 @@ def read_sentence(self, timeout=5):
             # Should be a full \r\n since the GPS emits spurious newlines
             if buf[-2:] == [ord("\r"), ord("\n")]:
                 # Remove line ending and spurious newlines from the sentence
-                return bytearray(buf).decode("ascii").strip().replace("\n","")
+                return bytearray(buf).decode("ascii").strip().replace("\n", "")
 
         raise TimeoutError("Timeout waiting for readline")
 
diff --git a/library/tests/conftest.py b/library/tests/conftest.py
index 8e1cb33..c119e3f 100644
--- a/library/tests/conftest.py
+++ b/library/tests/conftest.py
@@ -3,9 +3,28 @@
 import sys
 
 
+class SMBus:
+    def __init__(self, bus):
+        self.data = "$PMTK011,MTKGPS*08\r\n".encode("ascii")
+        self.ptr = 0
+
+    def read_byte_data(self, address, register):
+        if register == 0x00:
+            result = self.data[self.ptr]
+            self.ptr += 1
+            self.ptr %= len(self.data)
+            return result
+        else:
+            return 0
+
+    def write_byte(self, address, data):
+        pass
+
+
 @pytest.fixture(scope='function', autouse=False)
 def smbus():
     smbus = mock.MagicMock()
+    smbus.SMBus = SMBus
     sys.modules["smbus"] = smbus
     yield smbus
     del sys.modules["smbus"]
diff --git a/library/tests/test_setup.py b/library/tests/test_setup.py
index 37d3029..8e4e73e 100644
--- a/library/tests/test_setup.py
+++ b/library/tests/test_setup.py
@@ -3,3 +3,19 @@ def test_setup(smbus):
 
     gps = pa1010d.PA1010D()
     del gps
+
+
+def test_send_command(smbus):
+    import pa1010d
+
+    gps = pa1010d.PA1010D()
+    gps.send_command("$TEST")
+    gps.send_command("$TEST*")
+    gps.send_command("$TEST*".encode("ascii"))
+
+
+def test_recv_command(smbus):
+    import pa1010d
+
+    gps = pa1010d.PA1010D()
+    assert gps.update() is True