I needed to find a good nightlight for my son's nursery. But rather than just buying a traditional nightlight, I decided to make one that was a bit more decorative. I found a nice garden ornament in the shape of an owl that fit well with the other decorations in the nursery. I removed the original solar lighting circuit and replaced it with a new light and power adapter. The end result was a colorful owl nightlight.
Step 1: Materials
Here are the tools and materials that you will need for this project:
Owl Garden Ornament
Battery Powered LED Light
Heat Shrink Tubing (optional)
Rotary Cutting Tool
Soldering Iron and Solder
Step 2: Remove Any Unwanted Parts From the Garden Ornament
This garden ornament was originally a solar garden light. In order to turn it into a nightlight, I had to first remove the original circuit. I started by unscrewing the battery cover. This had the switch and the solar cell attached to it. The battery holder and the light were glued in place. So I used a rotary cutting tool to cut them free. I was careful not to damage the screw holes because I could use them to attach the new cover plate.
After removing the original circuit, I used an old toothbrush to clean out the dirt and debris that had accumulated inside the owl.
Step 3: Select a New Light Source for the Nightlight
Now you need a new light for the nightlight. One option is to build a simple LED assembly from scratch. Another option is to use a preassembled light. I decided to use the light from a small battery powered push light. I removed the housing so that I was left with just the LEDs and the circuit board.
Step 4: Measure the Output of the Power Adapter
In order to power the light, I decided to use a small AC power adapter. First cut off the end connector from the power cord. Then separate the wires and strip the insulation off the ends. Plug the adapter into an outlet and use a multimeter to measure the output voltage. Write this value down.
The multimeter will probably read a value that is larger than the output voltage listed on the side of the adapter. This is because the mutlimeter doesn't draw nearly as much current as the circuit that the adapter was designed to power.
Step 5: Calculate the Operating Voltage of the LEDs
If you do not know the operating voltage of the LEDs, then you need to calculate it. To do this, you need to first observe how the original circuit is wired together. The light assembly that I used was composed of three LEDs wired in parallel. They were originally powered by a three AAA batteries that were wired in series. The batteries were connected to the LEDs with a 10 ohm resistor.
Here is the formula for calculating the values of components used in a simple LED circuit.
LED Voltage = Battery Voltage - (LED Current x Resistor)
There are three 1.5 volt batteries in series. So the combined battery voltage is 4.5 volts. There are three LEDs wired in parallel with each other. LEDs typically have a current of 20 mA each. So the combined LED current is 60 mA (0.060 amps). Lastly, the resistor is 10 ohms. So we can calculate that the LED voltage = 4.5V - (0.060A x 10 ohm) which calculates to 3.9V. So these LEDs have an operating voltage of 3.9 volts.
Step 6: Replace the Resistor on the LED Assembly
Because the AC power adapter has a higher voltage than the original battery pack, we need to replace the resistor on the LED assembly with a higher value resistor. To determine the value of the resistor that we need, we can use the same formula that we used in the last step.
LED Voltage = Battery Voltage - (LED Current x Resistor)
This can be rewritten as:
Resistor = (Battery Voltage - LED Voltage) / LED Current
In this case the "Battery Voltage" is the voltage of the AC Power Adapter which is 7.8 volts. The LED voltage that we determined in the previous step is 3.9 volts. The LED current is still 60 mA or 0.060 amps. So the resistor that we need is:
Resistor = (7.8V - 3.9V) / 0.060A which is 65 ohms. The closest value resistor that I had was 68 ohms. That is close enough.
So I replaced the original 10 ohm resistor with a 68 ohm resistor. This will adjust the output of the AC power adapter so that it is appropriate for the LED lights that I am using.
Step 7: Test the Circuit by Connecting the Light to the Power Adapter
Now connect the positive output wire from the power adapter to the positive terminal of the LED assembly. Then connect the negative output wire from the power adapter to the negative terminal of the LED assembly. If there is a switch built onto the circuit board of the LED assembly make sure that it is in the "ON" position. The lights should now turn on.
Step 8: Insert the Power Cord Through the Side of the Owl
I decided that the best way to route the power cord into the owl was through the side of the owl near the base. This decision was mostly based on how I was planning to set up the nightlight in the room. It would also work to route it through the opening in the back.
To make an opening for the cord, I took a small drill bit and drilled a hole near the base. Then I inserted the cord through the hole and applied glue around the cord in the inside of the housing to help hold it in place.
Step 9: Add a Power Switch and Cover Plate
In order to turn the light on and off, I added a switch between the power adapter and the light assembly. I recommend using heat shrink tubing to cover the solder connection. If you do this, you must remember to slide the tubing onto one of the wires before soldering them together.
To cover up the opening in the back of the owl, I took a small piece of scrap plastic and cut it to fit the opening. Then I cut a small slot in the center for the switch. Then I glued the switch to the inside of the plate. To mount this cover plate to the back of the owl, I cut four small notches that lined up with the screw holes. Lastly, I fit the plate over the opening and secured it in place with the original screws.
Step 10: Finished Owl Nightlight
Now just turn on the switch and you have a decorative nightlight. This procedure can work with just about any decorative object that has openings for light to come out.