7-segment LED question

[[email protected]]

I'm looking for a 4 digit 7 segment LED setup. I got the idea from
ripping apart a really old PC case and looking at the nifty "MHz"
display. The whole thing was jumpered. I'm wondering if it's possible
to rip apart an alarm clock or even use a breadboard and real leds to
make a pseudo-hardwired 4 digit display that won't require a 12" x 12"
panel of wires and posts.

Is this possible or does anyone know of somewhere to <i>cheaply</i> buy
a jumpered/hardwired, 4-digit...thing?


Thanks!
Andrew

 

[Luhan Monat]

I'm looking for a 4 digit 7 segment LED setup. I got the idea from
ripping apart a really old PC case and looking at the nifty "MHz"
display. The whole thing was jumpered. I'm wondering if it's possible
to rip apart an alarm clock or even use a breadboard and real leds to
make a pseudo-hardwired 4 digit display that won't require a 12" x 12"
panel of wires and posts.

Is this possible or does anyone know of somewhere to <i>cheaply</i> buy
a jumpered/hardwired, 4-digit...thing?


Thanks!
Andrew

Check out the display on this project...

http://members.cox.net/berniekm/super.html

Is this what you are looking for?

 

[Spehro Pefhany]

I'm looking for a 4 digit 7 segment LED setup. I got the idea from
ripping apart a really old PC case and looking at the nifty "MHz"
display. The whole thing was jumpered. I'm wondering if it's possible
to rip apart an alarm clock or even use a breadboard and real leds to
make a pseudo-hardwired 4 digit display that won't require a 12" x 12"
panel of wires and posts.

Is this possible or does anyone know of somewhere to <i>cheaply</i> buy
a jumpered/hardwired, 4-digit...thing?


Thanks!
Andrew

Most displays these days are internally multiplexed. If you buy
individual digits (or some dual and a few 4-digit displays) and
assemble them you can tie the commons together to a supply and tie
whichever segments you want on (32 possible positions, counting the
decimal points) to the other side of the supply through resistors.


Best regards,
Spehro Pefhany

 

[[email protected]]

In that case, your example may work. I obviously though don't need
quite as much functionality. The circuitry would be easier I'm
assuming. Sorry, I've never done anything like this before.

 

[Luhan Monat]

In that case, your example may work. I obviously though don't need
quite as much functionality. The circuitry would be easier I'm
assuming. Sorry, I've never done anything like this before.

It may be that using a PIC may still be 'simplest'. A PIC16F818 may do
well (18 pin package) it can drive the requisite 12 lines while having a
few left over for digital/analog input.

 

[[email protected]]

That was my next question. What would I use to program what number to
display?

 

[Luhan Monat]

That was my next question. What would I use to program what number to
display?

Unless you are already set up for PIC programming, its going to be a
hell of a learning curve.

 

[[email protected]]

I'm thinking this is more trouble than it's worth...Thanks for the help
though!

 

[Rich Grise]

I'm thinking this is more trouble than it's worth...Thanks for the help
though!

It sounds to me like someone's blowing smoke up your butt.

Tear apart the clock. The four digits will be soldered to a PC board.
On the back of the board, you'll see their pins poking through, and
some traces. It shouldn't be hard to figure out which are the cathodes
and anodes of the LED chips - usually, there will be either one cathode
lead, and separate anode leads for the segments and punctuation, or the
other way around - one anode, and so on.

When you determine that, then if you have common-anode displays, stick
your positive voltage to the anode, and for each segment you want to
light, connect its cathode to ground through a 1K resistor.

If they're common-cathode, ground the cathodes, and apply the positive
voltage to individual segment anodes through a 1K resistor per each.

I'm assuming you have either a 5V logic supply or a 6V or so wall wart.
Four 1.5V cells in a battery holder will give you 6V. If you use a
12V wall wart, use 2K resistors.

Heck, you could even use the clock's own power supply and the dropping
resistors that came with the display, unless it has current-controlled
drivers. (then there wouldn't be any resistors).

As far as which segments to light for whatever digit, just light up
segments until you see something that looks like the number you want. ;-)

Nothing to it!

Cheers!
Rich