Divide by 4 counter with display

7400, 7476

Here's the divide by 4 counter you built back in Project Divide by 4 counter with the Display added. You can easily see the similarities by comparing the schematics for the two Projects.

As in the last Project Divide by 3 counter with display, most changes are in the line decoder to allow use of the Display. As in other counters you've played around with, the pulses for the counter generated by a transistor multivibrator. The counter circuit is an asynchronous type, since the Q output of the first flip-flop provides the clock signal for the second flip-flop. You can also see that two Diodes have been added to the decoder circuit — can you guess why?

If your memory is a bit rusty when it comes to diodes, take a look back at the diode section!

When you the power ON, you'll see 0 , 1 , 2 and 3 light up on the Display as the counter keeps track of the pulses from the multivibrator.

We've used multivibrators with these counter circuits simply because they're a handy source of pulses. You could just as easily do away with the multivibrator part of this circuit altogether and uses the Key to generate the pulses to be counted! Try it yourself, let your hand do the work instead of the multivibrator. (After all we've been using that circuit so much it deserves a vacation!)

You can also make connections to the Display so that the counter will indicate other numbers, small letters or capital letters as it counts the pulses. Can you figure out how to do this? Check back at those notes you made for 7 seg the diode section. We told you those notes would come in handy for you.

NOTES

When you first turn on the power the counter may not start with 0 and then 1, 2 and 3. Don't let that bother you. Most counters that you'll come across in electronic circuitry will be "reset" to start with and as a result will always start at 0. (By the way, the RJ terminal on the 7476 IC is for 'Reset/ or 'Clear' - which is used to reset the count to zero or clear the count)

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