Blue LED "moon lights" ??

[lyquidphyre]

example-
http://cgi.ebay.com/ws/eBayISAPI.dll...category=46314

But that is so expensive. (especially when people bid it up to like $50)

Is there anything different about the LED lights featured in those than regular blue LED lights? I figure it would be cheaper to "create" something than buy em on ebay or where ever else. I figure I could get a strand of blue LED lights from my friend Danny and come up with something and hook it to a timer...

What do ya'll think? Is that even good for fish? I don't see why it would be bad.. its not a laser or anything...

[patryuji]

Yes, it is very easy to make and inexpensive for the parts. Labor is the only thing that would add significantly to the cost.

Don't use superbright LEDs, do buy ones that have the most diffused pattern. For a dimmer you can simply add a potentiometer in series with the LED lights (which should be in parallel). Also have one resistor to limit the max voltage to equal what the LEDs are rated for. Current for LEDs is rarely greater than 30mA so you can use high gauge wire (20 gauge) without worry. The most expensive part should be the DC power supply (use a 5V adaptor if you can but a 9V with a larger limiting resistor can be used but it will just suck down more of your electricity and require a slightly higher watt resistor).

You could even create a gentle off switch by using an op-amp (cheap old u741 would be fine) in a voltage follower type circuit with the power supply tied into a small capacitor. A straight capacitor in the circuit would not work thus the voltage follower...also you would need to source the power from a BJT (such as a 2N3904) as the op-amp will not handle the current demands of multiple LEDs. Use the BJT in Common Collector mode to act as a simple switch.

(You can really ignore the last paragraph...but does this give you an idea of why a simple circuit may require a greater cost in terms of labor? Slapping parts together is easy, making a good sturdy circuit takes more care and planning).

[patryuji]

Here is a shopping list for you:

Solder
Wire
5VDC adaptor
Power jack for adaptor
60-70 ohm resistor (1/4watt)
1000 ohm potentiometer (may read 1K ohm pot)
LEDs...

Power__POT__________
|........................|......|......|
|......................LED LED LED
\___resistor___|___|___|

(ignore the periods as they are just spacers on the circuit diagram while lines represent wiring).

The + should go into the pot and the longer leg of the LED (positive side) should be up closest to the pot. The pot will be your adjustable dimmer (by limiting the current to the LEDs) and the resistor keeps the LEDs at around 3 volts.

You could do a "series" circuit but considering that each LED requires 3 volts to operate you will have to "scale up" the voltage source to match more LEDs. With the parallel circuit the voltage across each LED is set. Most power supplies will provide atleast 200mA (I think...) which is plenty for 5 HB(high brightness) LEDs.

[TankGirl]

Wow! Kudos to you for such a thorough, explanatory post! I'll just file the instructions and shopping list away for myself when I go to do this.

[patryuji]

Darn, my ASCII schematic didn't work....I'll have to fire up ORCAD and make an actual schematic and host it or something.

[edit]

nevermind I fixed the schematic.

[patryuji]

If anyone is interested I can modify the circuit above so that you can have a slowly dimming light (maybe over 4-6 seconds time period) as you turn the power off similar to what you experience in most newer cars when you shut the door and the dome light slowly dims.

[patryuji]

Okay, I made the circuit wrong...

You should do ONE of the following:

Either choose number of LEDs upfront and then (if each LED draws 30mA current):
1 LED requires the resistor to be around 60-70ohms
2 LEDs require the resistor to be around 30-35ohms
3 LEDs require the resistor to be around 20 ohms
All of these resistors are 1/4 watt.

-OR-
Remove the one resistor at the end and instead put an LED and resistor inline together. The resistor used with each LED should be 60-70 ohms. This is a far easier solution as it allows for more LEDs and resistors are usually sold 10 to a pack or more.

Get your diodes from www.lsdiodes.com and you'll save money over other sources.

Sorry for my error on the original circuit.

[Devilishturtles]

I caved in and bought the "miracle beam" LED lights for my fish tank. On clearance at wal-mart for like $5, originally $20. They are green and red and, IMO, provide just enough light for the "moon-light"effect. They are perfect, and do the same thing as the $100 moon light fixtures that you can buy in the pet stores (almost) =)

[lyquidphyre]

oh wow
Ill look into that!

[oscarbreeder]

They are perfect, and do the same thing as the $100 moon light fixtures that you can buy in the pet stores (almost)

Almost,
except the moon light on the water doesnt shine red and green.

You should try and get all blue ones that would look cool.