Just get 7 segment Working

[Tom McCurdy]

I am trying to get a 7 segment display to work...

I have acess to some of the 7400 series integrated circuits
I also have a 4511 integrated circuit

I had for long time a 555 going out to two 7490 divide by 10's to create led's counting in binary.... unfortuently I could never get that to work into the 7 segment display... I am now redoing the circuit from the beginning.

Anyone who could generate a diagram on how to make a 7 segment display work with 7490's a 555 and a 4511 would be my hero

anyway thx
-Tom McCurdy

 

[Tom McCurdy]

Please help

Any diagram would be extemly useful... we are not exactly sure what to do... or maybe we just hooked something up wrong last time

 

[jrz126]

I dont think you need to redo your entire circuit, You should just be able to adapt the BCD counters to output to the BCD-7seg drivers.

You could use a multiplexer and another 555 to switch between the 2 7 seg displays.

How high are you looking to count up to?
Also, could you post a schematic of what you got?

 

[Tom McCurdy]

Diagram

www.quantumninja.com/hw/Circuit.pdf

this is a picture of what is currently hooked up... I redid it today. I am not sure what to do with the final 3 leads of the LN514rk seven segment display. Also I was told today that the display may be a common cathode, which I belive would require a change from the 7447 to the 7448 driver.

Any help would be great.

 

[jrz126]

First off, I dont 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 isnt confusing, Feel free to send me an IM if you have any questions.

 

[Tom McCurdy]

still confused

I am still a bit confused on what needs to be done...
www.alldatasheet.com if you look here you can find the specifics for the LN514rk 7 segment display I am using... I am not sure whether it is common anode or common cathode

also I was basing the reistors off a sheet I was scanned.
right here
**broken link removed**

hmm
why can't I ever get this thing working

 

[jrz126]

Looks like you have common cathode (the K in the 514RK) So you either need a common annode display or a 7448.
This is probably why your circuit isnt working. try connecting LED's to the 7447, connect all the annodes to +5 and each cathode to a,b,c,d,e,f,g. and see what happens.

How do you have pins 3,4,5 set on your 7447?

 

[Roff]

I haven't looked at your schematic carefully, but I think you should get rid of the LEDs on the 7490 outputs, or buffer them. 7490 can only source 0.4ma (worst case) and still maintain a valid logic "1".

 

[Tom McCurdy]

THANKS!!!!

Thanks a lot especially to you jrz126... I finally got my circuit working... I actually figured out to replace the 7448 before you told me to... but thanks anyway I didn't know that you could tell that the 7-segment display was a common cathode from the K that is very helpful now... anyway the thing is counting beautifully and tomorrow I am going to attempt to add a second 7490 and 7448 to have two 7-segment displays. :twisted: :twisted:

thx again for all the help... I actually added my projet into the projects section... you may want to take a look at the final diagram.