Up counter using D Flip Flops

Thread Starter

Yami

Joined Jan 18, 2016
233
Hi, I'm try to make an up counter using D flip flops. All the Q outputs are connected to a BCD Ic to drive the seven segment display..it doesn't work :(. I tried connecting individual leds to the Q outputs and it counted from 0 - 13 in binary from. Now for some reason it doesn't do that even. I've attached a screen shot of the block diagram of how I have connected my FFs. I might have accidently given 5v to one of the FF Q outputs at one point- may it have damaged the IC (how would I check?). Also I don't really understand the clear and reset pins of the IC. D flip flop IC i'm using is 74LS74AP, for the clock I have a switch connected. Please help!
Thanks so much
 

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crutschow

Joined Mar 14, 2008
23,776
Applying 5V to the output could have damaged the circuit.
Look at all the outputs to see which is not working.

The clear and preset pins should be tied to +5V.

Using a mechanical switch for the clock will not work reliably without a debounce circuit to ignore the bouncing contacts when they close. Otherwise the circuit may see multiple clock pulses for each switch closure.
 

WBahn

Joined Mar 31, 2012
24,974
Using a chip without understanding what all of the inputs mean, or at least how they need to be configured to use it in the mode that you want, is a recipe for disaster. Get the data sheet for the part you are using and read about each of the inputs.

Applying 5V to one of the outputs might have damaged the chip. You can test it for basic functionality (which means knowing how it is supposed to function, which involves that pesky datasheet) but even if it appears to function properly the chip might still have been stressed and will fail much more quickly than it otherwise might have.

How did you apply the outputs to LEDs? Did you use an appropriate current limiting resistor?
 

Thread Starter

Yami

Joined Jan 18, 2016
233
Using a chip without understanding what all of the inputs mean, or at least how they need to be configured to use it in the mode that you want, is a recipe for disaster. Get the data sheet for the part you are using and read about each of the inputs.

Applying 5V to one of the outputs might have damaged the chip. You can test it for basic functionality (which means knowing how it is supposed to function, which involves that pesky datasheet) but even if it appears to function properly the chip might still have been stressed and will fail much more quickly than it otherwise might have.

How did you apply the outputs to LEDs? Did you use an appropriate current limiting resistor?
Yeah I did use 1K resistors. Both of my ICs are dead :( - but only one side is faulty of both the ICs :S.. and there is only one more D-flip flop in the local electronics shop. I think I would have to get two J-K FFs
 

KaiL

Joined Aug 30, 2014
69
Yeah I did use 1K resistors. Both of my ICs are dead :( - but only one side is faulty of both the ICs :S.. and there is only one more D-flip flop in the local electronics shop. I think I would have to get two J-K FFs
It is hard to know if the IC is faulty or not. Usually you would need a IC tester to check.

Even though most people dont have IC tester , there are still way to check if it is possible or note.

Make a simple design using only 1 FF and see if it works the way you want. If not , then yes it is faulty
 
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