diff --git a/docs/1b/ece124.md b/docs/1b/ece124.md
index 37b2271..b418f98 100644
--- a/docs/1b/ece124.md
+++ b/docs/1b/ece124.md
@@ -401,6 +401,12 @@ A **shift register** is a chain of redstone repeaters, consisting of a chain of
 
 An **up-counter** increments its binary value on input. A **down-counter** decrements its value. It is **synchronous** if all bits update simultaneously.
 
+### Counters
+
+A **Johnson counter** overflows by connecting the complement of the final output to the first input.
+
+A **ring counter** has exactly one output bit equal to one, looping when it reaches the end. It is equivalent to a loop of redstone repeaters, if redstone repeaters required input to switch to the next repeater.
+
 ## VHDL
 
 VHDL is a hardware schematic language.