elec mech and Rbeckett - Thanks, great help!!

One more question (SORRY!) If I were to use two single digit LED's driven by the same 9V battery, should I lower the resistor number, or leave them at 1k?

 

If I were to use two single digit LED's driven by the same 9V battery, should I lower the resistor number, or leave them at 1k?

Since the LEDs would be in parallel (not series) of the 9V battery, the resistor values remain the same.

 

Great, thanks a bunch!

 

Hey, sorry guys, me again. I went to order the parts tonight for my project when I realized...I don't know what wires I need! Just wondering what kind of wires I need to attatch the 9v battery to the resistors/segments.
Cheers!

 

Here's my previous advice.

For wire, I suggest 26 awg stranded, but 24, 28, or 30 would also work.

 

Oh, must of overlooked that. Thanks!
Would this here be good:
http://www.ebay.ca/itm/100x-Black-1...tDomain_0&hash=item1e709a4a3b#sfmsg_-7890|0|0@@

 

Oh, must of overlooked that. Thanks!
Would this here be good:
http://www.ebay.ca/itm/100x-Black-1...omain_0&hash=item1e709a4a3b#sfmsg_-7890|0|0@@

It will do, but if you are going to buy only one color, you might choose white, so you can use a sharpie to add coding marks to the wire.

 

Thanks a lot! I might end up getting black and red, but I'm not entirely sure yet.

 

Hey, this might sound crazy, but I was just wondering if it was okay to solder 66 wires (both positive and negative) to one of these battery packs? Or would that be too much?

 

Hey, this might sound crazy, but I was just wondering if it was okay to solder 66 wires (both positive and negative) to one of these battery packs? Or would that be too much?

There may be easier ways such as using solder lugs. You'll want to be able to remove the battery pack from the other wires so you can charge it and disconnect it quickly in the event of a problem.

Before going further however, what are these 66 wires going to? Could you post a rough schematic of what you intend to connect?

 

Here is my crazy schematic as to what I am doing.

 

Oops, forgot to add resistors to the schematic...ah well, you get the point!

 

Does the common lead require a resistor?

 

If all you want to do is light up certain segments, then follow Tracecom's schematic in post #9. You can leave off the individual switches going to each segment if you're not interested in using them. You don't need to wire up every segment if you're not planning on lighting it.

As shown in the schematic, you will need a resistor for each segment, but not the common cathode.

A 9V battery will not last long. You should be able to use a 4x AA battery holder to power these and it will last much, much longer.

If you decide to get further into electronics, you can make a PCB to better hold the displays and use ICs to control the numbers of each digit or make a count up/down counter, clock, etc.

 

If I used the 4 AA batteries, would I need a new resistor to replace the 1k ohms resistors?

 

Some basics, Ohm's law:

E = IR

where,
E = voltage
I = current in amps
R = resistance in ohms

For calculating LED current-limiting resistors we take the voltage of our power supply and subtract the forward voltage of the LED we are using.

Based on the datasheet I found earlier, each LED will take 2.2VDC.

Let's do the math:

6VDC (4x AA batteries: 1.5V each placed in series to get 6V) - 2.2V (LED forward voltage) = 3.8V.

Therefore, we need to put 3.8V across the resistor.

There is no information on the current required by the LEDs, so we'll assume a maximum of 20mA or 0.02A. 0.56in 7-segment displays don't usually require this much current - 10mA should work fine as well unless you really want them bright.

So, back to Ohm's law:

E = IR

3.8V = 0.02 * R

R = 3.8 / 0.02 = 190Ω (220Ω is common and would work fine) resistor per LED for really bright display

OR

3.8V = 0.01 * R

R = 3.8 / 0.01 = 380Ω (390Ω is common and would work fine)

Also need to verify correct resistor wattage: P = EI where P is power in watts.

P = 3.8 * 0.02 = 0.076W - a 1/4W resistor should therefore be fine.

So a 1kΩ would be okay, but the display may seem dim - no harm in trying in on a single digit and seeing what you think.

I'd strongly suggest an optical filter of some sort as well. This will make the display look sharper and easier to read. If using red LEDs, a transparent piece of red plastic like red Plexiglas or 0.01in thick red plastic sheet from a hobby store would work nicely.