diff --git a/src/main.c b/src/main.c
index 77c8ca4..9f4e009 100644
--- a/src/main.c
+++ b/src/main.c
@@ -12,7 +12,8 @@
 
 #include "ultrasonic_driver.h"
 
-#define ULTRASONIC_CYCLES 0x05U
+#define ULTRASONIC_CYCLES     0x05U
+#define ULTRASONIC_TRAN_US    50  // (ms)
 
 /*!
     \brief      main function
@@ -47,7 +48,7 @@ int main(void)
 
     while(1)
     {
-        delay_ms(50);
+        delay_ms(ULTRASONIC_TRAN_US);
         ultrasonic_pwm_out_cycles(ULTRASONIC_CYCLES);
         // printf("Send ultra sonic driver signal!\r\n");
     }