diff --git a/README.md b/README.md
index 554fa23..20760f3 100644
--- a/README.md
+++ b/README.md
@@ -10,6 +10,7 @@ Still, the performance is quite remarkable, and mostly limited by the implementa
 ![1MHz](doc/SQ-1MHz.jpg)  
 
 Above image shows 1MHz square waves on both output channels. It must be noted that the R value in the ladder networks is 0.5k in channel A and 1k in channel B, nicely showing the low-pass effect. 
+## Prototype circuit
  
 ![Proto-schematic](doc/Proto-schematic.gif)