Making a Counter

The purpose of a counter is to count events. A counter can be made in various ways. Assuming the occurence of the event gives a digital high, here is how a digital counter could be made. There are readymade counter IC's available. There are 0-9, 4 bit, 7bit, 8 bit, 12 bit, etc counters available, which require just a clock, precisely the occurence of the event bit as input, and with each high input, it increments. You can visit here 

for more information about these IC's.

Counters can also be easily made using just flip flops and logic gates. Let us design a 4 bit counter.

Following table shows what we exactly want :

4 Bit Asynchronous Counter:

A 4 bit asynchronous counter is pretty easy to make. By observation it can be seen that, whenever the input is 1, the LSB always toggles. The second bit toggles whenever there is a negative edge on the LSB, the third bit toggles whenever there is a negative edge on the second bit and the MSB toggles whenver there is a negative edge on the third bit. Therefore, the input could be used as a clock to the LSB TFF, its output could be used as a clock for the TFF containing the second bit and so on. Here is a block diagram to illustrate the same (assuming the TFF toggles on the negative edge)

4 Bit Synchronous Counter:

Observing the state table,

D0=A0 xor E

D1=A1 xor(A0.E)

D2=(A1.A0.E) xor A2

D3=(A2.A1.A0.E) xor A3

And here's the block diagram for the same:

Here's a video of the workinng of the imlementation, that we worked out: