diff --git a/dsp/main.c b/dsp/main.c
index 591711f..c09b058 100644
--- a/dsp/main.c
+++ b/dsp/main.c
@@ -9,32 +9,41 @@ void init() {
 }
 
 int main() {
+  led0->output = 37;
   init();
 
   while(1) {
+    led0->output = 42;
     uint8_t c = uart_read(uart0);
     uint16_t period;
     if (c == 'c') {
+      led0->output = 1;
       period = 1493;  // C4, 262.63 Hz, maybe
       uart_writen(uart0, "C4\r\n", 4);
     } else if (c == 'd') {
       period = 1330;  // D4, 293.66 Hz, maybe
       uart_writen(uart0, "D4\r\n", 4);
+      led0->output = 2;
     } else if (c == 'e') {
       period = 1185;  // E4, 329.63 Hz, maybe
       uart_writen(uart0, "E4\r\n", 4);
+      led0->output = 4;
     } else if (c == 'f') {
       period = 1119;  // F4, 249.23 Hz, maybe
       uart_writen(uart0, "F4\r\n", 4);
+      led0->output = 8;
     } else if (c == 'g') {
       period = 996;  //  G4, 392.00 Hz, maybe
       uart_writen(uart0, "G4\r\n", 4);
+      led0->output = 16;
     } else if (c == 'a') {
       period = 887;  //  A4, 440.00 Hz, maybe
       uart_writen(uart0, "A4\r\n", 4);
+      led0->output = 32;
     } else if (c == 'b') {
       period = 791;  //  B4, 493.88 Hz, maybe
       uart_writen(uart0, "B4\r\n", 4);
+      led0->output = 64;
     }
 
     square0->period = period;