Introduction: Glowing Stones LED Lamp
Many adults may remember building a lamp out of wood and decorating it with a soda can back in junior high school. This project is reminiscent of those days. My 13 yr. old daughter wanted to build a lamp and this made for a good lock-down, home-school science project.
After you build a project with LED strips, you’re often left with a section of left-overs, the part that you trimmed off to get an exact length to complete your project. This left over section lacks connectors, can be fairly short, and may not seem like it has an obvious use. This instructable will explain how to turn that leftover LED strip trimming into a decorative light.
My daughter wanted the light to have an automatic mode which used a photo-resistor to control part of the LEDs. We pulled from my electrical component stock to construct the circuiting. We added another LED array to the top which would be engaged in manual on mode for a higher light level. We chose a standard quart canning jar that had the desired aesthetics. We decided to wrap the LED strip around a cardboard tube to keep the lighting at a uniform distance from the sides and to reduce the number of glass beads required. She filled the remaining space with glass beads of various colors for a neat effect. The base was designed in Fusion 360 and 3D printed and it includes openings for the DC power jack, photo-resistor, and on-off-on toggle switch.
This project requires the following parts:
- LED strip(s) (new or leftover trimming)
- Glass canning jar with lid
- Colored glass beads
- Wooden, crafted, or 3D printed base
- Cardboard Tube (or 3D printed tube) and aluminum foil tape
- Power supply that matches the LED strip voltage.
- Wiring (18AWG or 20AWG) for making connections.
- Electrical Components
- DC plug and panel-mount socket
- Toggle switch for control, on-off-on in this case
- NPN transistor for automatic control (2N2222a)
- Photo resistor and ⅛ watt resistors to control the transistor.
Tools used include:
- Soldering Iron and silver-bearing solder (lead free)
- Multi-Meter Breadboard (for testing the circuit)
- Wire cutter/stripper
- Electrical tape
- Drill and bit.
- 3D printer or wood working tools (for the base)
Step 1: Glass Beads and the Light Tube
The first step is to determine the quantity of glass beads needed. In this case, we had three pounds of colored beads. It is important that the beads used are not electrically conductive due to the exposed metal surfaces of the LED tape. Glass marbles would be another option. The cardboard tube in the center helps reduce this quantity while keeping the LED strip consistently spaced from the sides of the jar. The tube was trimmed to length, taking into consideration that there would be glass beads on the bottom of the jar (eventually the top of the jar to hide the top LED array). To improve aesthetics and reflectance, this cardboard tube was covered in aluminum foil tape. The LED strip was adhered to the outside of the tube in a spiral pattern. There is an optional step to diffuse the light coming off the LED strip if a more uniform light pattern is desired - a cloudy material such as wax paper could be added around the strips. This would reduce some of the bright spots and would be a good idea if most of the beads are clear and not colored.
In order to reuse your LED strip, you need to solder wire to the tabs that are left when you cut the LED strip to length. Some kits have extra connectors which can be used. If you choose to solder, a small, solid wire is preferred for ease of soldering. I use 22awg solid wire for this purpose. A set of “helping hands” makes this task much easier. My daughter did the soldering as that was an important part of this lesson. This was her second time soldering and these connections were smaller than the previous task. She did a good job.
Step 2: Power Supply
A DC power supply is needed for this project. I’ve been collecting electronics parts for decades, so finding a suitable power supply was fairly easy. If you need to buy one for the project, you will pay attention to the DC Voltage output rating and the DC Current rating of the supply. If you want to reuse a spare you have laying around, you need to determine if it is regulated or non-regulated. Regulated (sometimes called “switching”) supplies have the same output voltage at any load (below rated load capacity). A non-regulated power supply will have an output voltage that varies with load, meaning it may be 18VDC with nothing connected and 10VDC with a heavy load connected. These supplies have a rated voltage output AT a specific load current, i.e. 12VDC @ 500mA. If you put more load on, voltage drops and, conversely, if you put less load on the voltage increases. You can use these if you want, but it requires a careful selection because exceeding the LED strip rating will cause them to fail more quickly (higher current through the LED chip increases brightness but decreases life). If you don’t know the load of your LED array(s), you can measure the load with a digital multi-meter when they are connected to a power supply. Our LED strips totaled 200mA of load and we used a supply rated for 600mA. For simplicity, I recommend using a regulated power supply for your DC voltage projects. The testing image shows using two meters to measure both voltage and current.
Step 3: Circuiting
The circuit design is fairly simple and there are a lot of options available to make it more or less complicated. An on/off toggle switch would be a very basic way to wire this up. We added a “dark sensor” circuit that turns the light on when the ambient light level is low and dims the light to off as the ambient light level increases. This circuit uses a voltage divider to control the voltage into the base of an NPN transistor.
In order to teach lighting control and circuit principles, we first built the circuit on a bread board. The power supply we used for the lamp was used for the bread board to provide realistic information. Here, we tried different resistor combinations to achieve the desired control. We referenced the datasheet for the NPN transistor and used a digital multi-meter to measure the resistance range of the photo resistor chosen (up to 10k ohm when dark). A 1k ohm resistor was added in series with the photo resistor to create the minimum value of the bottom of the voltage divider. A variable resistor is an optional feature for the top of the voltage divider to allow for adjustment, but we decided that a 22k ohm resistor on the top of the voltage divider provided adequate control and offered additional simplicity. These components were assembled on a small perforated board at the photo resistor location and soldered in-place. The LED strip is circuited through the collector-emitter portion of the NPN transistor, controlling the current through the LED strip. The difference between a “light sensor” and a “dark sensor” is simply the placement of the photo resistor in the voltage divider circuit (i.e. top or bottom). One complication to our circuit was the desire to have the internal strip be powered in AUTO or ON modes while the top LED array was only powered in the ON mode. A dual-pole toggle switch allowed for the internal strip to have isolated power feeds from the top array.
A panel mount DC jack provides a handy connection point and the mating plug was soldered onto the power supply wiring. Your power supply may already have a DC plug in which case you will just buy the matching panel mount jack. Be sure to pay attention to the polarity of your power supply plug, sometimes center is positive, sometimes center is negative. Knowing this is important because LEDs will only work with correct polarity.
Step 4: 3D Printed Base
The base was designed in Fusion 360 and is fairly basic. A rough shape was determined based on the dimensions of the jar and the height was based on the toggle switch depth. Holes for the jack and toggle switch were based on measured dimensions of the components chosen. The photo resistor location was recessed with cutouts for the leads, and a portion remained for the application of hot glue to secure the photo resistor. Mounting screw locations were also modeled and recessed so a printed lid could fit inside the base. The holes for the lid were slightly countersunk. M6 screw threads were modeled in the base. The wall thicknesses used were 2mm and the model was printed in PLA with 40% gyroid infill between 4 top and bottom layers. Layer height was .2mm with a .4mm nozzle. Take care to oversize your holes a bit to account for shrinkage after the print cools.
The attached images and files are a later version from the one we printed first, we took some lessons learned with and added a recess to screw the lid to the base. Our base omitted the recess and just sandwiched the base between the lid and the jar which required hot glue to prevent rotation. We want to build a few more of these and expect the design to evolve further over time. Feel free to use the attached files as a starting point for your project.
Step 5: Assembly
Assembly of this lamp was as follows:
- Clean all parts and pieces, the jar, lid, and beads.
- Insert a few layers on the bottom of the jar to obscure the top of the tube.
- Insert the tube with the LED arrays secured and wired.
- Leave several inches of extra wire length out of the mouth of the jar for connection later.
- Carefully add the glass beads as desired.
- We temporarily wired the LED array so my daughter could see the effect as she was adding beads.
- Once full, punch a hole in the lid and add a rubber grommet to protect the wiring from any sharp edges.
- Assemble the electrical components in the base.
- Assemble the lid and connect to the base.
- Glue or fasten the lid and base so that the jar cannot spin or be pulled away. In our case, the lid/ring to the jar secured the base to the glass jar, then hot glue was used to prevent rotation.
- Connect the LED wiring to the circuiting, two wires per LED strip/string/array.
- Install the lid.