Digital Clock using 74192 (RESET Button) HELP!

Thread Starter

nephelem

Joined Jan 24, 2016
20
Hi. I'm working on a project. A 24-Hour Digital Clock using 74192/74ls192 IC.There should be three buttons. 1.) Hour Increment Button 2.) Minute Increment Button 3.) Reset Button.

The schematic diagram is fine but I don't know how to connect the RESET button so that it will reset all 7 segment LEDs to 00 00 00. I did connect the RESET button (push-to-make switch) to VCC and the other pin to GND. Also the CLR/MR (Pin 14) of all the 74192 ICs but it output an incorrect display. Attached is my schematic diagram. Please help me. Thank you.
 

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AnalogKid

Joined Aug 1, 2013
8,251
I applaud you wanting to go old school with TTL, but the schematic is not fine.

ALL unused inputs must be connected to something, usually Vcc or GND, whichever renders them inactive.

SW1 and SW2 apply Vcc directly to the output of a 7408 gate. If you want to combine the button press with the output of a gate, you have to do it by either connecting the button signal to one of the gate inputs or by running the button signal and the gate output to the inputs of another gate. In your case you want to take the output of the gate and OR it with the button to drive the next stage clock.

All button signals need pull up or down resistors so the pins they are driving are not open circuits when the buttons are not pressed.

All LED segments need current limiting resistors.

You want to separate resetting each counter group from the master reset. You can do this, for example, by using the load input to load a value of zero into the tens-of-seconds counter when a 60 is detected. You have to change the three AND gates for NAND gates for this to work because the load input is active low.
 

dl324

Joined Mar 30, 2015
9,549
This is a project. It was there because I posted a reply from a post in the Homework Help forum. It's already moved here.
Your definition of project is different from the norm. If your project will be graded, it's homework.
 
Last edited:

djsfantasi

Joined Apr 11, 2010
5,912
You have stated in a post elsewhere that you have successfully pre-loaded the device. What do you think you can do with this knowledge to pre-load a zero into the counter? Effectively, this will clear the counter.
 

Thread Starter

nephelem

Joined Jan 24, 2016
20
You have stated in a post elsewhere that you have successfully pre-loaded the device. What do you think you can do with this knowledge to pre-load a zero into the counter? Effectively, this will clear the counter.
Yes, sir. CLEAR. Like the whole circuit will start again. 00 00 00 when i press the button
 

Thread Starter

nephelem

Joined Jan 24, 2016
20
I applaud you wanting to go old school with TTL, but the schematic is not fine.

ALL unused inputs must be connected to something, usually Vcc or GND, whichever renders them inactive.

SW1 and SW2 apply Vcc directly to the output of a 7408 gate. If you want to combine the button press with the output of a gate, you have to do it by either connecting the button signal to one of the gate inputs or by running the button signal and the gate output to the inputs of another gate. In your case you want to take the output of the gate and OR it with the button to drive the next stage clock.

All button signals need pull up or down resistors so the pins they are driving are not open circuits when the buttons are not pressed.

All LED segments need current limiting resistors.

You want to separate resetting each counter group from the master reset. You can do this, for example, by using the load input to load a value of zero into the tens-of-seconds counter when a 60 is detected. You have to change the three AND gates for NAND gates for this to work because the load input is active low.

Sir, what I mean is CLEAR. Like the whole circuit will start again from 00 00 00 when i press the button.
 

djsfantasi

Joined Apr 11, 2010
5,912
nephelem post: 957772 said:
Yes, sir. CLEAR. Like the whole circuit will start again. 00 00 00 when i press the button
You didn't answer my question. What can you do with the knowledge you have, that I pointed out?
 
Last edited by a moderator:

Thread Starter

nephelem

Joined Jan 24, 2016
20
i have applied that knowledge as you can see in the circuit. a very very little knowledge. what this knowledge i'm talking about is how to make the Tens of the seconds and the Tens of the Minutes be in Mod6 instead of Mod9. That's all the knowledge i knew.
 

Thread Starter

nephelem

Joined Jan 24, 2016
20
You didn't answer my question. What can you do with the knowledge you have, that I pointed out?

i have applied that knowledge as you can see in the circuit. a very very little knowledge. what this knowledge i'm talking about is how to make the Tens of the seconds and the Tens of the Minutes be in Mod6 instead of Mod9. That's all the knowledge i know.
 

AnalogKid

Joined Aug 1, 2013
8,251
Where are you located, and what is your native language?

What you don't seem to understand is that you need four separate Clear or Reset circuits: Seconds, Minutes, Hours, and Master Reset. You have three of them done already, and they look OK. Normally, adding a master Reset would require several logic gates, but you are fortunate and do not have to do this. Because the counters have a preset function built in, you can use this as a master reset by loading 0000 into each counter. Connect together the LD pin of all of the counters, connect this net to a pull up resistor to Vcc and to one side of the Reset switch. Connect the other side of the Reset switch to Ground. After you have made this change to your schematic, post the new version for us to review.

ak
 

Thread Starter

nephelem

Joined Jan 24, 2016
20
Country: Philippines
Language: Filipino (Tagalog) - Primary, American English (Secondary)

There is no device such called Pull-Up Resistor in Circuit Wizard. But according to google, i need to build it. I don't know if I constructed it correctly. Connected all the LD pins. IT WORKED O.O.. But i'm not sure.

Here it is:

74192revised1.jpg
 

Thread Starter

nephelem

Joined Jan 24, 2016
20
Where are you located, and what is your native language?

What you don't seem to understand is that you need four separate Clear or Reset circuits: Seconds, Minutes, Hours, and Master Reset. You have three of them done already, and they look OK. Normally, adding a master Reset would require several logic gates, but you are fortunate and do not have to do this. Because the counters have a preset function built in, you can use this as a master reset by loading 0000 into each counter. Connect together the LD pin of all of the counters, connect this net to a pull up resistor to Vcc and to one side of the Reset switch. Connect the other side of the Reset switch to Ground. After you have made this change to your schematic, post the new version for us to review.

ak
Sir, Do I need to connect the LT, BI and BL pins of all 7-segments to Vcc?
 

AnalogKid

Joined Aug 1, 2013
8,251
You do not have all 6 LD pins connected together, and the DN pins are connected incorrectly. The 7447 datasheet describes how to connect all of its pins.

ak
 

Thread Starter

nephelem

Joined Jan 24, 2016
20
You do not have all 6 LD pins connected together, and the DN pins are connected incorrectly. The 7447 datasheet describes how to connect all of its pins.

ak

Ah, yes. I missed one LD pin.
But did I build the pull up resistore correctly?
Where would I connect the DN pins of the Unit Counters? I only know how to connect DN pins of the Tens Counters.
I'll take a look of 7447 datasheet
 
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