Asynchronous counter
7400, 7476

Since we just found out about Synchronous counter, can you guess what an asynchronous counter is and haw it works?

Make it quick ,you're about to build one. You'll find this Project works almost exactly like the counter in the previous project.

When you put the power ON, you'll see that the LEDs operate as follows.

After both LEDs are off, then LED 1 will light while LED 2 stays off.

Then LED 2 will light while LED 1 goes out.

Then both LEDs will be off and the cycle will start all over again.

The key difference between synchronous and asynchronous counters can be found by comparing the schematic diagrams of this Project and the last one.

In a synchronous counter each flip-flop has its own clock signal input. But in an asynchronous counter (such as this one), the clock input for the second flip-flop comes from one of the outputs of the first flip-flop. It comes from the Q output of the first flip-flop in this Project.

The difference between synchronous and asynchronous counters might seem to be trivial but it's not. It takes time for the first flip-flop to set or reset and produce a clock signal for a second flipflop. When many flip-flop circuits are used (such as in a computer), this delay from the first flip-flop to the second can produce quite an error.

That's why synchronous counters are always preferred in circuits that are elaborate or where accuracy is important. In fact, you might be able to notice one side effect of an asynchronous circuit now.

Look carefully at the LEDs in this Project as they light on and off, can you spot any occasion where both LEDs are lit (even if only briefly)?