diff --git a/src/test_modulator.py b/src/test_modulator.py
new file mode 100644
index 0000000..516fb98
--- /dev/null
+++ b/src/test_modulator.py
@@ -0,0 +1,116 @@
+# test_modulator.py  27/03/2016  D.J.Whale
+#
+# Test the OOK modulator
+
+
+def ashex(data):
+    if type(data) == list:
+        line = ""
+        for b in data:
+            line += str(hex(b)) + " "
+        return line
+    else:
+        return str(hex(data))
+
+ALL_SOCKETS = 0
+
+def build_OOK_relay_msg(state, device_address=ALL_SOCKETS, house_address=None):
+    """Temporary test code to prove we can turn the relay on or off"""
+    #This code does not live in this module, it lives in an EnergenieLegacy codec module
+    print("build: state:%s, device:%d, house:%s" % (str(state), device_address, str(house_address)))
+
+    if house_address == None:
+        #this is just a fixed address generator, from the C code
+        #payload = []
+        #for i in range(10):
+        #    j = i + 5
+        #    payload.append(8 + (j&1) * 6 + 128 + (j&2) * 48)
+        #dumpPayloadAsHex(payload)
+        # binary = 0110 1100 0110 1100 0110
+        # hex    = 6    C    6    C    6
+        house_address = 0x6C6C6
+
+    payload = modulate_bytes([
+        (house_address & 0xFF0000)>>16,
+        (house_address & 0x00FF00)>>8,
+        (house_address & 0x0000FF)
+    ])
+
+    # Turn switch request into a 4 bit switch command, and add to payload
+    # D 3210
+    #   0000 UNUSED
+    #   0001 UNUSED
+    #   0010 UNUSED
+    #   0011 All off      (3)
+    #   0100 socket 4 off (4)
+    #   0101 socket 3 off (5)
+    #   0110 socket 2 off (6)
+    #   0111 socket 1 off (7)
+    #   1000 UNUSED
+    #   1101 UNUSED
+    #   1110 UNUSED
+    #   1011 All on       (3)
+    #   1100 socket 4 on  (4)
+    #   1101 socket 3 on  (5)
+    #   1110 socket 2 on  (6)
+    #   1111 socket 1 on  (7)
+
+    if not state: # OFF
+        bits = 0x00
+    else: # ON
+        bits = 0x08
+
+    if device_address == ALL_SOCKETS:
+        bits |= 0x03 # ALL
+    else:
+        bits += 7-((device_address-1) & 0x03)
+
+    payload += modulate_bits(bits, 4)
+    return payload
+
+
+def modulate_bytes(data):
+    """Turn a list of bytes into a modulated pattern equivalent"""
+    print("modulate_bytes: %s" % ashex(data))
+    payload = []
+    for b in data:
+        payload += modulate_bits(b, 8)
+    print("  returns: %s" % ashex(payload))
+    return payload
+
+
+MODULATOR = [0x88, 0x8E, 0xE8, 0xEE]
+
+def modulate_bits(data, number):
+    """Turn bits into n bytes of modulation patterns"""
+    # 0000 00BA gets encoded as:
+    # 128 64 32 16  8  4  2  1
+    #   1  B  B  0  1  A  A  0
+    # i.e. a 0 is a short pulse, a 1 is a long pulse
+    print("modulate_bits %s (%s)" % (ashex(data), str(number)))
+
+    shift = number-2
+    modulated = []
+    for i in range(number/2):
+        bits = (data >> shift) & 0x03
+        modulated.append(MODULATOR[bits])
+        shift >>= 2
+    print(" returns:%s" % ashex(modulated))
+    return modulated
+
+
+#----- TEST APPLICATION -------------------------------------------------------
+
+print("*" * 80)
+
+ALL_ON  = build_OOK_relay_msg(True)
+#ALL_OFF = build_OOK_relay_msg(False)
+
+print("ALL ON")
+print(ashex(ALL_ON))
+
+#print("ALL OFF")
+#print(ashex(ALL_OFF))
+
+# END
+