First init.

libraries/Adafruit_seesaw_Library/examples/NeoKey_1x4/basic_callback/basic_callback.ino

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+#include "Adafruit_NeoKey_1x4.h"
+#include "seesaw_neopixel.h"
+
+Adafruit_NeoKey_1x4 neokey;  // Create the NeoKey object
+
+//define a callback for key presses
+NeoKey1x4Callback blink(keyEvent evt) {
+  uint8_t key = evt.bit.NUM;
+  
+  if (evt.bit.EDGE == SEESAW_KEYPAD_EDGE_RISING) {
+    Serial.print("Key press ");
+    Serial.println(key);
+    neokey.pixels.setPixelColor(key, Wheel(map(key, 0, neokey.pixels.numPixels(), 0, 255)));
+    
+  } else if (evt.bit.EDGE == SEESAW_KEYPAD_EDGE_FALLING) {
+    Serial.print("Key release ");
+    Serial.println(key);
+
+    neokey.pixels.setPixelColor(key, 0);
+  }
+
+  // Turn on/off the neopixels!
+  neokey.pixels.show();
+  return 0;
+}
+
+
+void setup() {
+  Serial.begin(115200);
+  while (! Serial) delay(10);
+   
+  if (! neokey.begin(0x30)) {     // begin with I2C address, default is 0x30
+    Serial.println("Could not start NeoKey, check wiring?");
+    while(1) delay(10);
+  }
+  
+  Serial.println("NeoKey started!");
+
+  // Pulse all the LEDs on to show we're working
+  for (uint16_t i=0; i<neokey.pixels.numPixels(); i++) {
+    neokey.pixels.setPixelColor(i, 0x808080); // make each LED white
+    neokey.pixels.show();
+    delay(50);
+  }
+  for (uint16_t i=0; i<neokey.pixels.numPixels(); i++) {
+    neokey.pixels.setPixelColor(i, 0x000000);
+    neokey.pixels.show();
+    delay(50);
+  }
+
+  // set callbacks
+  for(int i=0; i<NEOKEY_1X4_KEYS; i++){
+    neokey.registerCallback(i, blink);
+  }
+}
+
+void loop() {
+  // we handle all key events with the callbacks
+  neokey.read();
+
+  delay(10);    // don't print too fast
+}
+
+
+
+/******************************************/
+
+// Input a value 0 to 255 to get a color value.
+// The colors are a transition r - g - b - back to r.
+uint32_t Wheel(byte WheelPos) {
+  if(WheelPos < 85) {
+   return seesaw_NeoPixel::Color(WheelPos * 3, 255 - WheelPos * 3, 0);
+  } else if(WheelPos < 170) {
+   WheelPos -= 85;
+   return seesaw_NeoPixel::Color(255 - WheelPos * 3, 0, WheelPos * 3);
+  } else {
+   WheelPos -= 170;
+   return seesaw_NeoPixel::Color(0, WheelPos * 3, 255 - WheelPos * 3);
+  }
+  return 0;
+}