diff --git a/prepend.txt b/prepend.txt
index 6d5ee6d..5b1bcc0 100644
--- a/prepend.txt
+++ b/prepend.txt
@@ -10,3 +10,14 @@
 
 
 #define LUA_SCRIPT_SIZE 10100
+
+// Knock is on ADC3
+#define KNOCK_ADC ADCD3
+
+// knock 1 - pin PA3
+#define KNOCK_ADC_CH1 ADC_CHANNEL_IN3
+#define KNOCK_PIN_CH1 Gpio::A3
+
+// Sample rate & time - depends on the exact MCU
+#define KNOCK_SAMPLE_TIME ADC_SAMPLE_84
+#define KNOCK_SAMPLE_RATE (STM32_PCLK2 / (4 * (84 + 12)))