Let's Make Robots!

Binary Clock Parts

Hey guys, I was thinking of making a binary clock. I don't want this to end up being the typical Dent work- I want this to be good looking and long lasting. It's going to be hung up on one of our walls, so I must be very precise.

Right now, I'm trying to find the right parts. I'll be spending my parent's money after all, so I want this to stay cheap (but still look good!) and I wanna get all the right parts the first time around. 

The enclosure is going to be an aluminum one from Halted. The LED's are probably going to be the 10mm blue ones from SFE. I'll also be getting a 5v Arduino Pro OR build my own from various parts to save money. A 3.3v regulator for the LEDs, plus a bunch of resistors to dim them slightly so they're not overwhelmingly bright. To drill the perfect circles that I'll need for the LEDs in the aluminum, I'm going to try a method that I was though of the other day. Since I don't have a drill press, I'm going to trace on the circles, punch out the center with a Dremel, and use those holes as guides for a larger (hopefully 10mm) drill bit that I'm going to have to use on my larger, albeit slower-spinning drill. 

If anyone has advice or suggestions, please let me know!

 UPDATE: I'm having extreme difficulty choosing between a pre-built arduino or one that I build on my own. What do you think I should do? Making one seems easy enough, but I'm worried that my absymal soldering skills will destroy it before I can even start this project...

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If you find yourself some nice LED bezels it'll mean you don't have to be as accurate on drilling the LED holes, the LEDs will be easier to mount, plus the finished product will look really nice.

What will this clock be powered by? You may find the regulator for the LEDs is not worth the effort.

Neat! I well definitely look into that. The clock will be powered by a wall adaptor. I don't know if I really need the regulator, but since they're 3 volt LEDs I thought I might as well include one. Plus, I want to bring down the brightness a little so the clock doesn't turn into a big blue hall light.

The adaptor should put out a nice stable voltage, so you can either have the regulator + N x LEDs + N x resistors, or just  N x LEDs + N x resistors. Either was you can simply start with the smallest safe current limiting resistor and gradually increase the resistance until the test LED is dim enough, then use that value for all the LEDs.

What are the LEDs going to be driven by, the Arduino directly?

I'm just using a regulator to drop the voltage. They seem fairly simple, just three pins (VIN, GND, VOUT). And no, I'm not driving the 10mm LEDs off of the Arduino; I'm going to use two Darlington drivers. Two because they're only 8 channels, and I have 11-13 LEDs.
The darlington drivers will probably drop at least 0.9V themselves, so if your LEDs need 3V or more your 3.3V regulator won't provide enough voltage. I should point out that using just the resistors gives you just as much brightness control and wastes no more energy than the regulator would have in the first place.

As Telefox said, use resistors. You can adjust the brightness of the LEDS. And a few resistors are much cheaper then a voltage regulator as you have to take care on your budget ;-)

You think I should wire a potentiometer to the common ground of all the LEDs? Seems like a fairly simple and versatile solution.

No. This would only work if always only one LED is ON. You need a resistor for every LED. Calculate the resistor according to the color of the LED and the operating voltage of your clock. Calculation goes here for example: http://led.linear1.org/1led.wiz

I have another idea. Connect a LDR on the analogue input. Then you can dim the LEDs by PWM according to the brightness in the room.

Adding an LDR would be a really interesting idea. But why won't the trimpot work? Doesn't it bring down the voltage/current for all the LEDs?
As soon as you connect all the LEDs to a common resistor the brightness of the LEDs will start to become uneven. There's a bit of natural variation in any batch of LEDs, and the LEDs that run at a lower voltage will draw more current - if other LEDs are also sharing a common resistor, they'll be deprived of current and appear dimmer.
Connecting a resistor the the common ground of the darlington arrays can also cause them not to trigger properly, since their ground reference is no longer stable.
PWM is also much more power efficient =)