diff --git a/README.md b/README.md
index 49268e2..03a88c6 100644
--- a/README.md
+++ b/README.md
@@ -144,6 +144,7 @@ There are several features that can be added to the rig if you want to. This is
 done by adding and removing `#define` lines to `settings.h`.
 
 - `OPT_BAND_SELECT`: change the band by pressing RIT for 2s.
+- `OPT_AUTO_BAND`: auto-select bands using a PCA9536 PIO (thanks VK3IL).
 - `OPT_ERASE_EEPROM`: erase the EEPROM by holding RIT for 8s.
 - `OPT_STORE_CW_SPEED`: store the CW speed in EEPROM.
 - `OPT_DFE`: direct frequency entry by holding the encoder button for 1s.
@@ -209,6 +210,8 @@ Some images of the connections:
 
 ## Changelog
 
+- 2017-05-16:
+  - `OPT_AUTO_BAND` (PR [#22](/../../pull/22) by VK3IL)
 - 2017-05-12:
   - VK band plans (PR [#21](/../../pull/21) by VK3IL)
 - 2017-05-04:
diff --git a/SODA_POP/SODA_POP.h b/SODA_POP/SODA_POP.h
index 03beeb5..85c251f 100644
--- a/SODA_POP/SODA_POP.h
+++ b/SODA_POP/SODA_POP.h
@@ -87,6 +87,11 @@ byte memory_index_character;
 #define EEPROM_CW_SPEED  7 // 1 byte
 #endif
 
+#ifdef OPT_AUTO_BAND
+#define PCA9536_BUS_ADDR 0x41	// I2C address for PCA9536
+#undef OPT_BAND_SELECT
+#endif
+
 #endif
 
 // vim: tabstop=2 shiftwidth=2 expandtab:
diff --git a/SODA_POP/SODA_POP.ino b/SODA_POP/SODA_POP.ino
index b84841b..1e8eeb5 100644
--- a/SODA_POP/SODA_POP.ino
+++ b/SODA_POP/SODA_POP.ino
@@ -70,6 +70,7 @@ Si5351 si5351;
 #define IF_DEFAULT 491480000
 
 byte memory_pointer;
+byte errno; // Global error number for S_ERROR
 
 const int MUTE = A3;
 const int TXEN = 13; // production A0
@@ -142,11 +143,18 @@ void setup()
   TIMSK1 |= 1 << OCIE1A;
   interrupts();
 
+#ifdef OPT_AUTO_BAND
+  state.state = EEPROM.read(6) == 0xff ? S_CALIBRATION_CORRECTION : S_DEFAULT;
+  read_module_band();
+#else
   state.band = (enum band) EEPROM.read(6); // check for operating band
   if (state.band == BAND_UNKNOWN) {
     state.band = (enum band) 0;
     state.state = S_CALIBRATION_CORRECTION;
+  } else {
+    state.state = S_DEFAULT;
   }
+#endif
 
   fetch_calibration_data(); //load calibration data
   si5351.set_correction(cal_value); //correct the clock chip error
@@ -155,7 +163,6 @@ void setup()
   invalidate_display();
   delay(1000);
 
-  state.state = S_DEFAULT;
   invalidate_display();
   digitalWrite(MUTE, LOW);
 
@@ -194,7 +201,7 @@ void loop()
     case S_CALIBRATION_PEAK_RX:     loop_calibration_peak_rx(); break;
     case S_ERROR:                   loop_error(); break;
     default:
-      error();
+      error(1);
       break;
   }
 
@@ -237,6 +244,11 @@ void loop_default()
     state.idle_for = DISABLE_DISPLAY_AFTER - 500;
 #endif
 
+#ifdef OPT_AUTO_BAND
+  if (tcount % 5000 == 0) // Check the band module for changes every 5s
+    read_module_band();
+#endif
+
   if (key_active()) {
     state.state = S_KEYING;
   // Tuning with the rotary encoder
@@ -795,8 +807,12 @@ void loop_calibration_peak_if()
     EEPROM.write(EEPROM_IF_FREQ + 1, state.op_freq >> 8);
     EEPROM.write(EEPROM_IF_FREQ + 2, state.op_freq >> 16);
     EEPROM.write(EEPROM_IF_FREQ + 3, state.op_freq >> 24);
-
+ #ifdef OPT_AUTO_BAND
+    EEPROM.write(6, 0); // Reset the "not calibrated" flag now that we've written the cal values
+    state.state = S_CALIBRATION_PEAK_RX;
+#else
     state.state = S_CALIBRATION_CHANGE_BAND;
+#endif
     invalidate_frequencies();
     invalidate_display();
 
@@ -865,7 +881,7 @@ void key_handle_end()
     state.state = S_DEFAULT;
   } else if (state.state == S_MEM_ENTER) {
     if (memory_pointer == MEMORY_LENGTH) {
-      error();
+      error(2);
       return;
     }
     buffer[memory_pointer++] = morse_char;
@@ -1089,10 +1105,78 @@ void ee_erase()
  * Enter the error state. This error is non-recoverable and should only be used
  * in very rare cases.
  */
-void error()
+void error(byte er)
 {
+  errno = er;
   state.state = S_ERROR;
+}
+
+#ifdef OPT_AUTO_BAND
+/*
+ * Read the input latch of the PCA9536 and return a 4-bit value
+ * If the band module can't be read or the value is out of range, display an error and wait for a valid band module
+ */
+byte PCA9536_read()
+{
+  for (boolean err = true; err; err = false) {
+    Wire.beginTransmission(PCA9536_BUS_ADDR);
+    Wire.write(byte(0x00));       // We read only from register 0, the input latch
+    Wire.endTransmission(false);  // Transmit repeated start rather than stop at end of transmission
+    Wire.requestFrom(PCA9536_BUS_ADDR, 1);
+    if (Wire.available() != 1) {  // Unable to read the band module ID (most
+                                  // likely it's not plugged in properly, or being changed!)
+      err = true;
+    } else {
+      byte reg_val = Wire.read() & 0x0f;
+      if(reg_val < 2 || reg_val > 11) // Module has an un-supported configuration
+        err = true;
+    }
+    if (err) {
+      state.display.digits[3] = LED_N_6;
+      state.display.digits[2] = LED_n;
+      state.display.digits[1] = LED_E;
+      state.display.digits[0] = LED_r;
+      state.display.dots = 0x0;
+      delay(500);
+    }
+  }
   invalidate_display();
+  return reg_val;
+}
+
+/*
+ * Check if the band module has changed and if it has, reset bandlimits and operating frequency
+ */
+void read_module_band()
+{
+     enum band new_band;
+
+     switch (PCA9536_read()) { // Map returned value to current band table range
+       case 2:   new_band = BAND_160; break;
+       case 3:   new_band = BAND_80;  break;
+#ifdef BAND_60
+       case 4:   new_band = BAND_60;  break;
+#endif
+       case 5:   new_band = BAND_40;  break;
+       case 6:   new_band = BAND_30;  break;
+       case 7:   new_band = BAND_20;  break;
+       case 8:   new_band = BAND_17;  break;
+       case 9:   new_band = BAND_15;  break;
+       case 10:  new_band = BAND_12;  break;
+       case 11:  new_band = BAND_10;  break;
+       default:  new_band = BAND_UNKNOWN; error(3); break;
+     }
+
+     if (new_band != state.band) {
+       digitalWrite(MUTE, LOW);  // Make sure we are in receive mode
+       state.band = new_band;
+       setup_band();             // Set the band limits and default
+                                 // operating frequency for the selected band
+       display_band();
+       delay(2000);              // Allow time to view the band on the display
+       invalidate_display();
+     }
 }
+#endif
 
 // vim: tabstop=2 shiftwidth=2 expandtab:
diff --git a/SODA_POP/buttons.ino b/SODA_POP/buttons.ino
index 1d0fced..b486b38 100644
--- a/SODA_POP/buttons.ino
+++ b/SODA_POP/buttons.ino
@@ -150,7 +150,7 @@ unsigned int time_encoder_button()
 }
 
 /**
- * Debounche the keyer button.
+ * Debounce the keyer button.
  */
 void debounce_keyer()
 {
diff --git a/SODA_POP/display.ino b/SODA_POP/display.ino
index ad56ec1..249f013 100644
--- a/SODA_POP/display.ino
+++ b/SODA_POP/display.ino
@@ -165,8 +165,8 @@ void invalidate_display()
     case S_ERROR:
       state.display.digits[3] = LED_E;
       state.display.digits[2] = LED_r;
-      state.display.digits[1] = LED_r;
-      state.display.digits[0] = 0x00;
+      state.display.digits[0] = LED_DIGITS[errno / 10];
+      state.display.digits[0] = LED_DIGITS[errno % 10];
       state.display.dots = 0x2;
       break;
   }
diff --git a/SODA_POP/settings.h b/SODA_POP/settings.h
index df867b7..8ab9125 100644
--- a/SODA_POP/settings.h
+++ b/SODA_POP/settings.h
@@ -38,6 +38,9 @@
 /* Band selection by pressing RIT for 2s */
 #define OPT_BAND_SELECT
 
+/* Autoband selection based on plugged in module with PCA9536 PIO */
+//#define OPT_AUTO_BAND
+
 /* Erase EEPROM by pressing RIT for 8s */
 #define OPT_ERASE_EEPROM
 
@@ -48,7 +51,7 @@
 #define OPT_DFE
 
 /* Disable display when idle */
-#define OPT_DISABLE_DISPLAY
+//#define OPT_DISABLE_DISPLAY
 #define DISABLE_DISPLAY_AFTER 2500 /* Time to disable display after, in ms */
 
 /* More message memories. Select using the rotary encoder. */