Add "hash encoding" to generate a value for unknown encodings.

For an unknown encoding, an arbitrary 32-bit value will be generated.

Author: shirriff

IRremote.cpp

@@ -368,11 +368,10 @@ int IRrecv::decode(decode_results *results) {
  if (decodeRC6(results)) {
  return DECODED;
  }
- if (results->rawlen >= 6) {
- // Only return raw buffer if at least 6 bits
- results->decode_type = UNKNOWN;
- results->bits = 0;
- results->value = 0;
+ // decodeHash returns a hash on any input.
+ // Thus, it needs to be last in the list.
+ // If you add any decodes, add them before this.
+ if (decodeHash(results)) {
  return DECODED;
  }
  // Throw away and start over
@@ -599,3 +598,57 @@ long IRrecv::decodeRC6(decode_results *results) {
  results->decode_type = RC6;
  return DECODED;
 }
+
+/* -----------------------------------------------------------------------
+ * hashdecode - decode an arbitrary IR code.
+ * Instead of decoding using a standard encoding scheme
+ * (e.g. Sony, NEC, RC5), the code is hashed to a 32-bit value.
+ *
+ * The algorithm: look at the sequence of MARK signals, and see if each one
+ * is shorter (0), the same length (1), or longer (2) than the previous.
+ * Do the same with the SPACE signals. Hszh the resulting sequence of 0's,
+ * 1's, and 2's to a 32-bit value. This will give a unique value for each
+ * different code (probably), for most code systems.
+ *
+ * http://arcfn.com/2010/01/using-arbitrary-remotes-with-arduino.html
+ */
+
+// Compare two tick values, returning 0 if newval is shorter,
+// 1 if newval is equal, and 2 if newval is longer
+// Use a tolerance of 20%
+int IRrecv::compare(unsigned int oldval, unsigned int newval) {
+ if (newval < oldval * .8) {
+ return 0;
+ } 
+ else if (oldval < newval * .8) {
+ return 2;
+ } 
+ else {
+ return 1;
+ }
+}
+
+// Use FNV hash algorithm: http://isthe.com/chongo/tech/comp/fnv/#FNV-param
+#define FNV_PRIME_32 16777619
+#define FNV_BASIS_32 2166136261
+
+/* Converts the raw code values into a 32-bit hash code.
+ * Hopefully this code is unique for each button.
+ * This isn't a "real" decoding, just an arbitrary value.
+ */
+long IRrecv::decodeHash(decode_results *results) {
+ // Require at least 6 samples to prevent triggering on noise
+ if (results->rawlen < 6) {
+ return ERR;
+ }
+ long hash = FNV_BASIS_32;
+ for (int i = 1; i+2 < results->rawlen; i++) {
+ int value = compare(results->rawbuf[i], results->rawbuf[i+2]);
+ // Add value into the hash
+ hash = (hash * FNV_PRIME_32) ^ value;
+ }
+ results->value = hash;
+ results->bits = 32;
+ results->decode_type = UNKNOWN;
+ return DECODED;
+}

IRremote.h

@@ -56,6 +56,9 @@ class IRrecv
  long decodeSony(decode_results *results);
  long decodeRC5(decode_results *results);
  long decodeRC6(decode_results *results);
+ long decodeHash(decode_results *results);
+ int compare(unsigned int oldval, unsigned int newval);
+
 } 
 ;
 

examples/IRrecvDump/IRrecvDump.pde

@@ -28,26 +28,24 @@ void setup()
 void dump(decode_results *results) {
  int count = results->rawlen;
  if (results->decode_type == UNKNOWN) {
- Serial.println("Could not decode message");
+ Serial.print("Unknown encoding: ");
  } 
- else {
- if (results->decode_type == NEC) {
- Serial.print("Decoded NEC: ");
- } 
- else if (results->decode_type == SONY) {
- Serial.print("Decoded SONY: ");
- } 
- else if (results->decode_type == RC5) {
- Serial.print("Decoded RC5: ");
- } 
- else if (results->decode_type == RC6) {
- Serial.print("Decoded RC6: ");
- }
- Serial.print(results->value, HEX);
- Serial.print(" (");
- Serial.print(results->bits, DEC);
- Serial.println(" bits)");
+ else if (results->decode_type == NEC) {
+ Serial.print("Decoded NEC: ");
+ } 
+ else if (results->decode_type == SONY) {
+ Serial.print("Decoded SONY: ");
+ } 
+ else if (results->decode_type == RC5) {
+ Serial.print("Decoded RC5: ");
+ } 
+ else if (results->decode_type == RC6) {
+ Serial.print("Decoded RC6: ");
  }
+ Serial.print(results->value, HEX);
+ Serial.print(" (");
+ Serial.print(results->bits, DEC);
+ Serial.println(" bits)");
  Serial.print("Raw (");
  Serial.print(count, DEC);
  Serial.print("): ");