diff --git a/src/experiment.c b/src/experiment.c
index a240e5b9394ffe8a3b45a16bae501d3a4cfe4733..c6a766677786adc4a114139b4520f9c7272b74fe 100644
--- a/src/experiment.c
+++ b/src/experiment.c
@@ -1005,6 +1005,7 @@ static void manual_experiment(void){
     tc_set_direction(&EXP_TC0_0, TC_UP);
     
     EXP_TC0_0.CNT = 0;
+    printf("R\n");  // signal ready
     
     while (1){
         if (udi_cdc_is_rx_ready()){