7-Seg LED + Enc , Dec and Latches

Status
Not open for further replies.

he11fire

New Member
What I want to achieve through this experiment is that when I press , let's say button 2 , the display not only show the number but also save it until another number is pressed ...I am trying to make this happen through latches but I got confused from the Set Inputs...The reset inputs shouldn't change I guess from Truth Table of these Active Low Latches ...The buses are connected with each other so it is not a problem for the circuit ...I'm waiting for any suggestion ...

This is the circuit :
**broken link removed**
 
The circuit may be more straightforward to use a 74HC573 Octal D-Latch rather than a set reset. Then all you need to do is generate a clock signal which would be OR-ed from your pushbuttons.
 
hi,
The LS177 outputs an inverted BCD pattern depending upon which key is press that sets an input low, so the inverters will change the sense of the BCD pattern to regular BCD.
The outputs from the inverters should go to the SR inputs of the LS279, the BCD pattern will then be input to the LS47.

The problem is that you will have to Reset the LS279 latches in order clear the them as you press the next switch, use the R inputs of the LS247 linked together to do the reset.
So you will need some additional logic from the switches.

OK.??
 
Last edited:
Hi
ericgibbs said:
hi,
The LS177 outputs an inverted BCD pattern depending upon which key is press that sets an input low, so the inverters will change the sense of the BCD pattern to regular BCD.
Click to expand...
What integrated circuit is ls177 ?? ...it wasn't on multisim (the program above) nor google ...
The outputs from the inverters should go to the SR inputs of the LS279, the BCD pattern will then be input to the LS47.
Click to expand...
You are saying I should use also R inputs of the latches...I thought only S inputs needed to change from 0 to 1 in order the latch memorizes the input.
The problem is that you will have to Reset the LS279 latches in order clear the them as you press the next switch, use the R inputs of the LS247 linked together to do the reset.
So you will need some additional logic from the switches.
Click to expand...
What do you mean the R inputs of LS247 ? ...
Do I need an extra switch to clear the state before I press another button?
Thanks in advance.
 
hi,
The LS177 was a typo should have been LS147, sorry if thats caused you a problem.

The LS279 are quad NAND gate type latches.
To Set a latch to a high '1' output the SR input/s is switched low '0' and it will remain Set until the R reset pin is switched low.

This means when the SR input low level has set the latch output high, the SR input can go high again but it will not reset the latch, only a low on the R input will reset the latch.

You need to detect the leading edge of a switch press, use the edge to Reset all the latches, after the edge reset the latches will be set to the BCD patter of the pressed switch.

OK.?

EDIT:
On the HC147 you should have pull up resistors on the input pins.
I see you have them, on the top of the drawing.!
 

Attachments

  • 000esp11.gif
    5.7 KB · Views: 291
  • 000esp12.gif
    58.8 KB · Views: 380
Last edited:
To Set a latch to a high '1' output the SR input/s is switched low '0' and it will remain Set until the R reset pin is switched low.
Click to expand...
From the Truth Table I know that the latch will set if S=0 and R=1 ...if they're both 1's latch memorizes last state and continuous so, if they're both 0's it causes an invalid state because we don't know how Q is going to be(at least at this kind of latch) ...

This means when the SR input low level has set the latch output high, the SR input can go high again but it will not reset the latch, only a low on the R input will reset the latch.
Click to expand...
What you're saying should be wrong from the truth table.

You need to detect the leading edge of a switch press, use the edge to Reset all the latches, after the edge reset the latches will be set to the BCD pattern of the pressed switch.
Click to expand...
I don't understand very well what you mean ...how can I detect 'the leading edge of a switch press' ...what is it ?
Thanks for your time.
 
Last edited:
hi,
I would suggest that you use a 74LS373 Octal latch that uses an 'enable' to latch the data or a 74LS374 that uses a 'clock' signal to latch in place of the 74LS279.

For the 'enable or clock' , consider a 9 input AND gate, it could be made up from diodes and resistors
When you press any switch the output of the AND would go low, connect the low going pulse to an inverter via a capacitor/resistor [ differentiating the leading edge] and use the high output pulse of the inverter to 'enable or clock' the latch.

Do you follow that OK, or do you need a simple diagram.?
 
another way you can think of it is to latch your inputs when the button is pressed, it can be done using a 4017 with a fast clock. when you press one switch the particular out put will come high and remains until you press the other button. see the attached cct.

Edit: missed to attache the cct.
 

Attachments

  • prog select.JPG
    28.4 KB · Views: 392
Last edited:
4017 according to google is a counter ...it might work ...I don't know and that's the problem ...I'm trying to figure this out from my knowledge and I still haven't learned the counter ...I'm in my first year of electronics and until now what I have learned is Flip-Flops, 555 and latches ...
Thanks in advance.
 
4017 is a decade counter, but can be used as i mentioned, i recently made such a selection latch for a school exhibition project for my daughter, it works fine.

if you follow its very simple to understand how it works. the enable input should be kept zero to enable the counting, here its connected to supply voltage via a high resistor, when a particular button is pushed then it makes the enable input to go low making the counter to count, until the particular out put connected to the push button becomes high then the counter enable goes high. this stops the counter on that state.
 
Yes u can do this .when u use cd 4511. Decimal to binry convert, via diode 1n4148 . 4 lach one transistor npn
 
he11fire said:
Why did u use only 6 LEDs ?
Why do you connect the reset with output 6 ?
Click to expand...

this drawing i made for another post long before for some one who needed channel selection for 6 inputs, the feed back resets teh counter after 6th LED, even you can keep it not connected sop that it would go until 10counts to internally reset. using one IC you can go up to 10 LED / out puts, there is a way you can connect two ICs and go up to 20 selections, that is what i made recently for my daughter.
 
Last edited:
The idea is good but the circuit you provided is wrong ...since CP1 will never be low so the counter counts ...?
Why does the button when pushed , make CP1 low ...
This circuit doesn't work.
 
it may not work for simulations, but it works in real, see the attached pic of some game i made for my daughter, it just work fine without any problem, when ever a push button is pressed the LED lights up for that selection.

CP1 is the enable input of 4017, and can be pulled to low when connected to any of the out put that is low (current sink).
 

Attachments

  • game-1.JPG
    134.6 KB · Views: 392
  • game-2.JPG
    186.7 KB · Views: 287
I see...can you tell me how did you connect the 7-Seg LED in the circuit because the connection in the first circuit you attached was for ordinary LED.
7-Segment LED always needs the Decoder and the Encoder sometimes , as I've seen until now.
Thanks for your time.
 
I used 4026 (counter & 7 segment driver) for the display....great the same you can use it to diplay the numer of the selection of 4017, do as on the attached diagram, my program doesnt have 4026 in the library so coudnt complete the drawing, check the data sheet for how to connect it.

CD4026BE Datasheet pdf - CMOS Decade Counter/Divider with Decoded 7-Segment Display Outputs and Display Enable - Texas Instruments

when you press a push button either it will reset 4017 IC before lighting the LED or wil not reset, in both cases the display 4026 will show you the selection number.

Edit: new diagram attached to inhibit the clock to 4026
 

Attachments

  • 4026 with 4017.JPG
    35.6 KB · Views: 1,032
Last edited:
Status
Not open for further replies.

Similar threads

K
  • Question
led after glow
Replies
14
Views
3K
Tony Stewart
S
  • Question
Help LED Flood lamp power supply reduce flicker and current
Replies
11
Views
3K
christinescoms
C
  • Question
7555 pulsating led
2 3 4
Replies
64
Views
10K
Tony Stewart
B
  • Question
Traffic lights and push button
Replies
3
Views
2K
AnalogKid
O
  • Question
WTB: NSM3915 LED Bar Graph Module
2
Replies
33
Views
9K
techpeople1
T
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…