Electronic Lock using 74LS74 DTFF

[_q12x_]

Thanks for those 2 pages. I actually have a VERY long history with bouncing buttons in my circuits, with various implementations (RC, 555) if you might even remember some of them, but I have these issues from long before you. And I come across, 'a time or two' (to paraphrase someone, haha) in my life over Denouncing ICs and I always overlook them. I think it is time to commit to take some of them IF they are cheap enough in bulk. I'll have to check it ! Very good reminder, looking over your 2 pages ! Thanks.

Yes, I give it a quick look over ebay and aliexpress and they are not cheap. Especially in bulk. Damn. When I say -in bulk- I refer to 100pcs, minimum.
Heh, 74HC00 used as a debouncing IC, that is very new to me ! Very interesting.
-I do know about RC debouncing cct, but to be very sincere, I did neglect it in my previous project. I forget about it. I was concentrated to the other important aspects of the larger cct. It is a good reminder though !

 

[marconi]

I have an interesting question:
View attachment 107295

For a permanent 1 input connect direct to 5V and for a permanent 0 connect to 0V.

 

[marconi]

https://www.electronics-tutorials.ws/logic/pull-up-resistor.html

Use pull up or pull down resistors when an input has a switch connected to an input or control pin to enable 0 or 1 to be selected.

 

[_q12x_]

I have 2 interesting Questions for anyone here looking to my posts.
-Question1- What is the role of that 4011 NAND gate in the original cct ?
I have 3 Theories about its role.

• T1: The role of the NAND gate is to automatic deactivate S1 to S8 AFTER LED1 is ON, by setting HIGH the first 3 Gates Reset pins, resetting them, until S9 or S10 is pressed, that in turn will reset only the 4th gate.
• T2: If it is indeed a gate used to reset the first 3 FF's, why in the hell didn't do it like I did it? Linking all 4 Reset pins together. I am still absolutly perplexed why he used it there. It still has no sense to me. The only logical sense is if it was having some LEDs there, that he didnt wanted to keep them open when the last digit in the opening code was activated. For curious eyes, not to see which leds/buttons were activated. But it is not having any LEDs in the cct either. It is a true mystery that NAND gate there.
• T3: The designer didnt know anything about logic ICs and he slap it there, just because, no reason whatsoever. Just to make a Bigger cct, for appearances that it is 'complicated' and fancy. He might be an idiot.

- - -
-Question2- Now the fun part! Hehehe. I already solved this problem. I worked on it probably 1 day and I figure out a solution. It is working fine in simulator, but I didn't test it on the breadboard. But I will very soon, just to be sure. If you like to play logic games, like I do, give it a try. I will post the cct I made, but after awhile. Not right now. I will give you time to think.
So... the cct we are using is from post #8 and the problem is like this:
- How would you add a LED for each Switch in the cct? To light when the button is pressed, but not all LEDs at once! Only when you press a certain button, its corresponding LED, let's say it's "parallel" LED, will lit up, telling you THAT button is in pressed state.
I will give you a hint. There are 2 sets of switches. 1 set are all linked between them and to the Reset pins, and 1 set are the ones for the Clocks. You will have to adapt to each set.
Again, I solved the problem and it is a very cool one. Haha. Happy designing !
Im very curious if you will come with the same or similar solution as mine, or completely different approach. Or nothing at all. Haha. Good luck. Let's see who will be the winner ! Haha.

 

[marconi]

I suggest you think first about what effect the series RC circuit of C1 and R7 has. So consider:

a. What is the waveform at U2B-Q* pin 12?;

b. What will the waveform be at the point where C1 and R7 join together in response to the waveform at a?;

c. How does U3A's output respond - the waveform which is sent to the Reset R inputs of the previous FFs - when it has as its input the waveform at b above?;

d. Now consider what would be the reset waveform with out using U3A, C1 and R7 which is the way you think it should be done.

e. Finally what effect do the two schemes have on the operation of the lock circuit including how the LEDs illuminate?

 

[_q12x_]

Here is the progress so far. Only 4/6 button modules are made so far. In the final cct I linked 6 Reset pins toghether and 4 buttons for clock pins. In total 10 btns. I tested what I have here and working just fine. But is hard work and slow. Slowly but surely.
All the components are scrapped and repurposed. Those leds are VERY old, 80's or 90's and quite dim to today standards. But bright enough for this application.

 

[_q12x_]

All 6 Reset Button modules are made. Quite an effort and patience.

 

[_q12x_]

Here is the Clock Button:
Only 1 now, and I have to make 4 of them. Its much simpler than the Reset buttons.

+ a little test

 

[_q12x_]

All the buttons + leds [modules] are done. What a day ! Phiew.

 

[_q12x_]

I managed to finish the Lock circuit. The final cardboard with everything on it. I also made a movie about it showing how it is functioning. WOW. Im very happy it worked from the first try ! I was very slow and careful when I build it. Also checked it many times while I was constructing it. Im very relieved I made it. Ohoha !

 

[_q12x_]

And, for completion, here is the end of the project.
I am not allowed to put videos here in this website; So if you google this:
q12 #208 Electronic Lock - Final Project Done
you will be able to see my final movie about it.
Also this one as well, why not:
q12 #207 Electronic Lock - The (card)board circuit finished
and also this one:
q12 #206 Electronic Lock - How I make an electronic (card)board circuit