How can I get a seven segment display to light up in my circuit?

[Tom McCurdy]

Hello all, you may remeber from past about the circuit I was working on to get a simple 7 segment display to work... we had to tangent from that for awhile but we are finally back...

I got frustrated with problems in the 5 bread board circuit with around 100 led's so I streamlined the circuit with my partner and it now contains the integrated circuits on one board. I am trying to figure out how to get this stupid seven segment LED to light up

Here is a diagram of what I currently have built- The 555 works and blinks the two leds, also the 8 other leds work and count... however the seven segment display does not work.
www.quantumninja.com/hw/Circuit.pdf

I am not sure what to do with the final leads for the seven segment display

the parts used are
555-integrated circuit
7490-integrated circuit *2
7447-integrated circuit
LN514rk seven segment display
http://www.alldatasheet.com/datasheet-pdf/view/PANASONIC/LN514RK.html
specs for seven segment display

if link doesn't work just search www.alldatasheet.com for specific parts to get spec sheets

I don't know what to do to make it work please help!

 

[bryce1]

Do you have pins 3 and 4 of the 7447 tied high? I don't see it on the schematic. Look at the truth table for the 7447.

Do you also have pins 3 and 14 of the display tied to gnd?

 

[Tom McCurdy]

Um no I don't ...I was just told to tie the other pins of the display to positive... hmm

 

[Tom McCurdy]

First off, I don't think you need those current limiting resistors between the 7 seg and 7447, It has internal current limiting.

For the 3 remaining pins, I'm assuming that your 7 seg display has 10 leads total: 7 for the display (a,b,c,d,e,f,g) then you have 2 commons, (are they common annode?) and the final lead is for the decimal.
Usually the 2 commons are in the middle of the top and bottom.

It looks like the 7447 should be able to support common annodes. Just connect the 2 commons to your +5 volts.

looking at your drawing, You also need to connect pin 8 of the 7447 to ground.
Looking at the truth table for the 7447, you want pin 3 (Lamp test) high, if you bring this low, it should light every segment of your display, a good way to check it. You also want your blanking input (pin 4) high. and I think you will want pin 5 high as well.

Hope this isn't confusing, Feel free to send me an IM if you have any questions.

One thing I was also considering was making sure that the LN514rk 7 segmetn display is common anode as opposed to common cathode... becasue if its common cathode wouldn't I need the 7448 instead of the 7447?

 

[Tom McCurdy]

What I really need to know is the connections between the 7447 and ln514rk ... what goes ground what goes positive

 

[Janus]

What I really need to know is the connections between the 7447 and ln514rk ... what goes ground what goes positive

Your common cathodes (pins 3 & 14) should go to gnd.

 

[Tom McCurdy]

HAHAHAHAHA I got it!

I realized that the led was common cathode and so switched the 7447 with a 7448 and it worked

thanks a lot for the help though guys... does anyone know of any free software taht streamlines circuits drawings?