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An LED throwie is a battery-powered LED taped to a coin cell, usually with a small magnet attached so it can stick to a steel surface. To make the basic version, connect the LED’s long lead to the positive side of a 3 V CR2032 coin cell and its short lead to the negative side, then tape the parts securely together. Keep the short lead clear of the battery’s positive rim to prevent a short circuit.
What you need for a basic LED throwie
The basic build needs no soldering or special tools. Make: specifies a 10 mm diffused LED, a CR2032 coin cell, a small disc magnet, and strapping or electrical tape. A diffused LED spreads its light rather than concentrating it into a narrow beam.
- One 10 mm diffused LED
- One 3 V CR2032 coin cell
- One small disc magnet
- Strapping or electrical tape
These are recipe examples, not a recommendation for a particular product. An O’Reilly Media excerpt from Make: Easy 1+2+3 Projects also lists a ½-inch by 1-inch plated NdFeB disc magnet and one-inch strapping tape. O’Reilly’s excerpt does not establish that these specifications are required; a small magnet and tape are the essentials.
How to assemble the throwie
- Find the LED leads. The longer lead is the anode; the shorter one is the cathode.
- Make the electrical connection. Press the long lead against the CR2032’s positive side and the short lead against its negative side. The LED should light when both leads make contact. The positive contact extends around the battery’s rim, so keep the short lead from touching that rim. Make: and Science Buddies’ LED Stickies activity describe the same basic polarity.
- Secure the LED and cell. Wrap tape around the battery and leads so they stay in contact. Make: calls for a 7-inch piece of strapping or electrical tape and a tight wrap to help prevent flickering.
- Attach the magnet. Place it against the battery’s positive side and continue wrapping tape to hold it in place. The assembly can then attach to ferromagnetic material, such as steel.
If the LED does not light, check that the leads are on the correct sides and making contact. Do not try to fix a poor connection by letting the short lead touch the positive rim.
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Ways to make the design more elaborate
Add an off tab
A simple sliding contact can interrupt the circuit and turn the LED off. Before wrapping the assembly, place the long LED lead between two small cardstock tabs. Tape one tab in place and leave the other free to slide: moving it separates the lead from the battery contact, and sliding it back restores contact. Make: describes this as an on-off tab; it is an alternative to leaving the LED lit continuously.
Link throwies into a bug
Make: describes linking multiple throwies into segments to create a larger, bug-like design. The added sections can make the assembly more cumbersome, and the project notes that very long chains may not stick as well. Keep the result somewhere you can retrieve all its components.
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Build a PVC lantern
Make:’s “Indestructible LED Lantern” places an LED in a drilled PVC cap and uses a binder clip and battery inside a PVC enclosure. The project page describes the lantern as weatherproof and says it floats and survives rain and ice; those are the project’s claims, not independently verified performance results. Drilling and mallet work call for suitable adult supervision and safe tool handling.
Make LED jellies
Make: also presents “LED Jellies,” a decorative jellyfish-like variation. It is an art project built around the throwie idea, not a requirement for making a working throwie.
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Choosing a version
| Version | Build and tools | Can turn off? | Performance evidence | Recovery |
|---|---|---|---|---|
| Basic taped throwie | Simple; tape secures the LED, coin cell, and magnet. | No built-in switch in the basic recipe. | No controlled brightness or runtime results are provided. | Retrieve the whole unit and collect its cell and components. |
| Sliding contact tab | Adds two cardstock tabs; no special tool is specified. | Yes; sliding the tab breaks or restores contact. | No controlled runtime results are provided. | Retrieve the whole unit and collect its cell and components. |
| Linked throwie bug | Connect multiple throwies into segments. | No switch is specified for the linked design. | Make: notes that very long chains may not stick as well; no controlled test is provided. | Retrieve every linked section and collect its components. |
| PVC lantern | More involved; includes drilling a cap and fitting an enclosure, binder clip, and battery. | No switch is specified in the project description. | Make: describes it as weatherproof and says it floats and withstands rain and ice; independent testing is not established. | Plan a location where the enclosure can be retrieved and its battery recovered. |
Battery, runtime, and handling cautions
The direct CR2032 design does not include an external series resistor. Adafruit explains that a coin cell’s internal resistance can allow it to power an LED directly, but doing so stresses the cell and can shorten its runtime. Adding a resistor can improve longevity; choosing a value for another battery or LED requires information about that LED and supply. Do not assume the coin-cell arrangement works for a larger battery: Science Buddies specifically warns against using an AA cell without a resistor.
West Florida Components estimates that a continuously lit “glowie” lasts about a week. That is the site’s approximate estimate, not a controlled runtime test or a promise for every combination of LED, battery, and contact. Exact current, brightness, runtime for a particular build, and a resistor value for an alternative circuit are not established here. A switch can let you turn the light off and may extend operating life, but it does not create a universal runtime.
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Coin cells and small magnets are small parts. Keep loose cells and magnets away from young children, supervise the activity as appropriate, and follow the battery manufacturer’s handling and disposal guidance.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Use throwies responsibly
Do not attach throwies to bridges or other public structures. Adafruit’s LED project guidance cautions that leaving them behind is littering and creates electronic waste. Use only a permitted surface where every unit can be retrieved, then collect the battery, magnet, LED, and tape.
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