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 cheaply buy a jumpered/hardwired, 4-digit...thing?
Thanks! Andrew
Check out the display on this project...
Is this what you are looking for?
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
That one's a little bit much for what I want. I really don't think I need a chip since I will just flip a few wires/jumpers/whatever to change the digits.
I was only refering you to the 4 digit LED itself. It is a common anode multiplexed unit selling for under $3.
Also, you cannot 'hardwire' a multiplexed display. For that, you need seperate units.
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.
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.
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
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