help with digital circuit

[samcheetah]

i made a circuit that i have attatched to this post using Multisim7. it uses a numeric keypad ( that i havent made here ), a 74147 that will encode the decimals on the keypad to BCD, a 7447 that will decode the BCD to a 7 segment and a common anode 7 seg display. when i ground a pin on the input of the 74147 (provided other pins are high) the 7 seg display should show the corresponding number. but i dont understand what is the matter with this circuit. when i simulate it, it doesnt work. can someone plz help me out??????????????

 

[Optikon]

i made a circuit that i have attatched to this post using Multisim7. it uses a numeric keypad ( that i havent made here ), a 74147 that will encode the decimals on the keypad to BCD, a 7447 that will decode the BCD to a 7 segment and a common anode 7 seg display. when i ground a pin on the input of the 74147 (provided other pins are high) the 7 seg display should show the corresponding number. but i dont understand what is the matter with this circuit. when i simulate it, it doesnt work. can someone plz help me out??????????????

What happens with the simulation when it "doesnt work?"

Also, what does your simulator assume is happening to the pins that you are not connecting on the 7447? In a real circuit, you should pull these pins high or low. You might want to try that in the simulator, some of them are blanking pins.

 

[samcheetah]

well when i said it doesnt work i meant that the display shows nothing. none of the LEDs of the 7 seg glow up.

and about those pins. well i have tried every combination of those pins. first i kept one low and the others high and then i went on changing the levels of the pin. in a real circuit these pins should be kept open when using a single decoder.

can somebody plz help me out

 

[Sebi]

Maybe for simulating no need, but the supply pins must be connected. For TTL inputs always need logic level (also for unusable pins).

 

[carlosthejackle2001]

My pal had the same problem with this circuit in simulation, i can't remeber if he finally got it to work but he built it practically and it worked, he instead used a common cathode seven segment display.

 

[Optikon]

well when i said it doesnt work i meant that the display shows nothing. none of the LEDs of the 7 seg glow up.

and about those pins. well i have tried every combination of those pins. first i kept one low and the others high and then i went on changing the levels of the pin. in a real circuit these pins should be kept open when using a single decoder.

can somebody plz help me out

Have you probed (in your simulator) starting at U1 and working your way left to right in the circuit? In otherwords, do you know that your first stage is working or not? I assume you've done this and none of the logic circuit works. You know, the input of this inverter is changing but the output is stuck low..hmmm.. that kind of thing..

 

[kitedude]

are you sure its an anode and not cathode

 

[vaibhavi]

about digital ics

hello,
first of all sorry that i am replying you not for your querries but myself vaibhavi ,i'm completing my project on fastest finger first and as that project is based on Electronics Design Technology i want designing steps or selection of the ic's ,resistances,etc.
ic's are 7475 , 7420 , 74147 , 7447 , 7404. plzzz reply me or comment on that.