Introduction: LED Lightbulb
This was just a lark that had been itching in the back of my head for a while. It's a mains powered LED lightbulb.
Step 1: Supplies
There's not too many things you need for this project.
An incandescent light bulb.
A .47 microfarad 200V capacitor.
1/4 watt 1kilo ohm resistor
a pair of leds
and miscellaneous things.
Step 2: Assembly
You need to start by cleaning out the lightbulb, there are numerous instructables with this step and I will forgo it here.
The circuit consists of two LED's wired in opposition, I ground down the LED's just short of the die and glued them together to make a single double LED. Twist the legs of the LED's together, on one side solder the capacitor, the other the resistor. Simple.
Step 3: Test
Here I'm holding the circuit with a clothespin and sticking it into an outlet, this is of course, the recommended test procedure. ;-)
Step 4: The Bulb
Stick the circuit into the bulb and use some hot glue to hold it in place, be sure to have some cold water, you will burn you fingers. Try to center the LED in the bulb. Once you have the circuit in place, bend one of the leads over the base and secure it with aluminum tape. The second lead is twisted around a brass screw inserted into the hot glue. Check for shorts and you should be good to go.
Step 5: The How What and Why
First to address an oversight, you need a non polarized capacitor for this project, muy importante.
Now, how does this work? We all know that to run an LED off a higher than rated voltage source we muct limit the current with a resistor. Indeed in this case we could limit the current with a resistor of value approx. 6.8K ohms, however that resistor would need to dissipate several watts!!! Not a good thing.
Since we are using an AC source we can take advantage of a property of a capacitor subjected to AC called Reactance. We can equate reactance to resistance. Calculating the reactance is a simple formula
R=1/(2*Pi*Freq*C) Solving this for C will give us the size capacitor we need to limit the current to the LED.
So why do we have a resistor at all? When the power is switched on there is an in rush of current and the 1K ohm resistor is there to limit that in rush current.
Finally, Why two LED's? Well an LED is a diode and since we are dealing with AC here we need to wire two led's in opposition so that the waveform can complete it's cycle. Essentially each LED is flickering at 60HZ but in opposite phase.