Home > Circuit Bricks > BCD Counter
UPDATED:.21:00 21 October 2013

  • This circuit will count input pulses and generate a binary value from 0 to 9 on its outputs.
  • BCD = Binary Coded Decimal = Counts from 0 to 9 and then repeats.
  • Simple to use - two counters pers IC.

The circuit is based around the 4518 counter IC. It is a CMOS type and can work from a wide voltage range. The circuit shown will count input pulses. Leave inputs as they are if not using them.

It is a digital device and works with logic level inputs. A high refers to +v and low refers to 0v.


Circuit Diagram
  • Clock - A high pulse on this input increments the count
  • Enable - A low input will stop the counting.
  • Reset - A high input will reset the counter to zero.

The outputs A,B,C,D are binary signals, A is the LSB (Least Significant Bit), ie = 1

The output increments its value on every rising clock input. As it is a BCD counter, it counts from 0000 to 1001 (not 1111) and represents a decimal place..

Cascading means to join together in a chain. So to create another decimal place, a 10's, or 100's etc. the counters can be connected as shown right.

More places/counters can be added in the same way following these rules:

  • All Reset inputs are joined together
  • All Clock inputs (except the first) connected low (to 0v)
  • The D (8's) output must connect to the Enable input of the next counter.

An unlimited number of places can be added to count to very high numbers.

The 4518B counter comes in an 16pin DIL package and has 2 counters per package.


If possible use an IC holder so the IC can be removed easily and is not damaged from excessive heat while soldering.
IMPORTANT: Try not to handle the pins of the IC too much. They do have protection diodes connected inside but CMOS types are very sensitive to static charge.
Written by Phil Townshend - 2008
www.edutek.ltd.uk - Working Electronics For Students & Teachers