counter display using LED's

[lordsathish]

hello friends............
we are planning to make an count down timer for our college festival.......
the output of the counter IC 74192 is decoded using sevens egment display decoder IC 7447...... the out put of 7447 is used to drive the display in which each segment is made of a series of LED's.... this out put cannot drive all these LED's ........... if it is made to drive the display it is very dim...... is there any solution to make the LED's glow brighter..... Is using a relay,SCR or TRIAC a good solution..... if so how......... will we encounter any problems using them..... will the LED's last for one week........?

 

[audioguru]

The LEDs or ICs will blow-out in an instant if they aren't connected properly. Attach your schematic to avoid us guessing about it.

 

[andy257]

If i am reading this right why dont you just use a 7 seg display?

Unless you want a much larger display of course.

Keep in mind that some ic's can sink more current than they can supply. So if you can use an external supply rather than drive them from the ic. Just a thought.



Andy

 

[ljcox]

As Audio wrote, we need more information. My guess is that you do not have enough voltage behind the LED string. But you need to be careful as the 7447 will have a maximum voltage limit. I don't have a data sheet for it so I can't check.

If the 7447 is limited to say 6 Volt, then you will need either transistors or MOS FETs to act as buffers between the 7447 and the LEDs.

Post a circuit so we can help more.

 

[audioguru]

I couldn't find spec's for an old 7447 and haven't seen one for 35 years.
A SN7447A is still made and has outputs rated for 15V, 40mA.

 

[lordsathish]

I am using the 74190 and 74191 counter ic's to count down.....
My display should be large..... It should display the number of day,hours and minutes left out for a festival sheduled after a week....
Instead of using a 7segment display i'm using a display made out of LED's similar to 7segment one...... since my display is larger and is made of large number of LED's i cant connect the out put of BCD to 7seg decoder 7447.... so i need to use an external power supply to switch on the display LED's for this is it better to use SCR,TRIAC or relays........?i think realys will be costlier.....

 

[Nigel Goodwin]

since my display is larger and is made of large number of LED's i cant connect the out put of BCD to 7seg decoder 7447.... so i need to use an external power supply to switch on the display LED's for this is it better to use SCR,TRIAC or relays........?i think realys will be costlier.....

It's usual to use driver transistors, either BJT's or MOSFET's. If you were using mains powered lamps to make a HUGE display, then SCR's or TRIAC's would be the things to use, but not for LED's.

It's also likely to be FAR easier (and smaller and cheaper) if you use micro-controllers rather than TTL chips.

 

[spuffock]

Nigel, it would be easier and cheaper for YOU to use a PIC, but for someone completely new to the devices? I can still remember when, after pages of messages like " no target VDD" , " Wrong ident code" and "lost communication with ICD", I clicked on RUN, got the message"Running", and found myself looking it up to see what it meant.

 

[Nigel Goodwin]

Nigel, it would be easier and cheaper for YOU to use a PIC, but for someone completely new to the devices?

It would be easier and cheaper for anybody - it would probably be quicker to learn to program a PIC (which doesn't really take very long to learn) than to build such a device in hardware.

This is the 21st century!, why use 30 year old technology?.

 

[spuffock]

Several large boxes of 30 year old technology , free to collector?