There are some amazing color change LEDs available today that cycle between red, green, and blue. These are available in fast and slow change and contain a really small circuit that does the color changing. Also available are flicker LEDs, like what you will find in the flame-less candles that are popular today.
Of course, you could also just change your nightlight from a standard white light to a blue or green or pink LED as well. You can use whatever color you prefer, who wants a white LED anyway?
The parts you will need today include:
- An old LED-based night light (may need to look at the secondhand stores)
- A new LED. Use a slow color change, fast color change, flicker LED, or any color you prefer.
- A resistor. I used 2k ohm but you may choose to use a lower value, like 470 ohm.
- Fresh solder (I like this one)
We will also need the following tools
- Soldering iron, I like this in-expensive soldering station.
- A desoldering pump, these are cheap and work great.
- Wire cutters, these are amazing for under $5 bucks
Let's get started.
Step 1: Disassemble Nightlight
Your disassemble may be different than mine, I have seen a lot of variations in designs so you may need to play around with the best approach.
For mine, the first step was to break it apart, without actually breaking the top diffuser plastic. I tried multiple techniques and even broke one into multiple pieces before figuring out a simple track. It turns out that if I placed the night light in a vice and gave it a few sharp cranks, it would break the glue holding it together into two nice pieces. It can be re-glued later if needed, although they do hold themselves together with a good friction fit.
Once the diffuser is split, mine had a single screw holding the base unit together.
Before continuing, it would be a good idea to check the large capacitors for any lingering charge. Using insulated pliers, touch the two leads of the large capacitor. You may not know which it is, as mine only shows the back of the circuit board. In that case, hold one side of your pliers on the grounded plug (thick blade) and run the other across each of the leads. In general, it should have a discharge resistor but who knows.
Step 2: Mark and Desolder Old LED
Before you remove your old LED, mark the positive and negative leads. You can do this by pressing a coin-cell battery across the leads to determine which one is positive.
When desoldering, you will need to add some fresh solder to the joint. Add fresh solder and heat up the joint and the LED should fall out. If not, remove the old LED with wire cutters and use a solder sucker to remove the last bits of the leads along with any leftover solder.
Desoldering takes practices and patients.
Step 3: Check DC Voltage of Old LED
This is an optional step and only do this if you are comfortable with high-voltage AC.
Carefully plug the night light into an AC outlet or extension cord. Carefully cover the photoresistor with a long piece of heat shrink tubing to simulate full darkness.
Using your multi-meter, check the voltage across the two pads where the LED was soldered in place. Mine read just under 10 volts, which is way too high for a color change LED.
After determining the DC voltage, carefully unplug the nightlight and use an insulated needle nose pliers to discharge the capacitor on the board.
For mine, I want to add a 2k ohm resistor in series with my new LED, you may choose to use 470 ohm. You can calculate your resistor value using an online LED calculator like this one. In my case, I have a 10V supply voltage, a 15mA current with a 3V voltage drop, and one LED. A lower current will make your LED last longer and it won't be as bright.
Step 4: Add Resistor and LED
Mark on the LED which is the positive lead because when it gets cropped, we need to know its correct orientation. I used a sharpie to make a small dot on the negative side (short lead).
Crop the negative lead down to just a few millimeters, just enough to solder on our resistor. Do the same to one of the resistor leads and then solder them together. I like to flow solder on both parts and then re-flow them together. Use a helping hands if needed.
Next, crop the positive lead on the LED to the proper length by holding it in align with our final placement. Also crop the resistor lead, leaving enough room for the resistor to fit back into the casing without touching any of the other circuitry. If needed, use heat shrink tubing over the resistor to avoid a short circuit.
The final step is to confirm the polarity of your LED, add solder to the remaining leads and on the PCB pads, and the reflow them together.
Make sure your LED sits nicely in the light-pipe and diffuser.
Step 5: Reassemble and Enjoy
Make sure you get the photoresistor properly lined up with its hole before screwing the two parts back together. Carefully adjust the LED so that it is pointing straight up and that the resistor does not short out. If necessary, use a knife to trim the plastic around the LED's hole.
The night light I used needed to have the diffuser broken apart because it was glued or fused together. You may choose to re-glue it using super-glue. There is enough friction where the diffuser and base meet to hold it together so I'm not going to glue mine.
Give it one last test in a dark room.
Now you have a custom nightlight. Enjoy!