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An LED throwie is a small LED powered by a coin-cell battery and held to a ferromagnetic surface by a disc magnet. The basic build takes a few minutes: match the LED leads to the battery’s polarity, tape them securely, then attach the magnet. From there, you can add a simple on/off control or build more elaborate versions such as a PVC lantern, glowing jellyfish, or programmable light.
What you need for a basic LED throwie
- One LED
- One coin-cell battery
- One small disc magnet
- About 7 inches of electrical or strapping tape
The LED’s longer lead is the anode, or positive lead; the shorter lead is the cathode, or negative lead. The magnet holds the finished light to a ferromagnetic surface, such as iron or steel. It will not attach to every metal.
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How to make an LED throwie
- Test the polarity. Pinch the LED leads against the coin cell: place the longer lead against the positive (+) side and the shorter lead against the negative (–) side. The LED should light.
- Tape the leads in place. Cut about 7 inches of tape and wrap it tightly around the battery and leads. A secure wrap helps prevent flickering from a loose connection.
- Add the magnet. Place the disc magnet against the battery’s positive side and continue wrapping with tape to hold the parts together.
- Check for a short. Make sure the LED’s cathode does not touch the battery’s positive edge. That contact can short the circuit.
- Attach and remove it carefully. Set the magnet against a ferromagnetic surface. To remove the throwie, slide the magnet sideways while lifting an edge with a fingernail or tool, rather than pulling straight away from the surface.
What battery does an LED throwie use, and how long does it last?
The basic build uses a coin-cell battery. The Make: instructions do not specify one battery model for every basic throwie; the lantern variant below specifically uses a CR2032. Make:’s 2012 article, updated in 2015, estimates that a throwie glows for 1–2 weeks, depending on weather and LED color. That is an approximate project figure, not a controlled battery-life test, so actual runtime can vary.
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Make: describes several variations that change how a throwie attaches, behaves, or is built. Their reported performance is specific to those project versions, not a guarantee for every build.
#1 Best Overall
- Overview: 5 mm Frosted Foggy Round Small Lens (Viewing Angle: 20 degrees) 2 leads, 5 colors x 20pcs = 100pcs Mixed Leddiode, 20 for Each Single Color (White Red Green Blue Yellow)
- White: 6000K-9000K(7000K 8000K) Red: 620nm-625nm Green: 515nm-520nm Blue: 455-465nm Yellow: 588-592nm(590nm 591nm)
- Shipping Weight: 0.04kg, (Pack of 100) (5 Colours, Each Color 20pcs / Through Hole DIP 2pins 5mmled LEDs Set)
- Compatible with: Indicator Lights, DIY PCB Circuit, Arduino, Raspberry Pi, hobby, Science Experiments, Colorful Throwies Project, Breadboard, T1 T-1 Bulb, Bulk 3.2v 3.3v Parts Replacement,Invisible Black Light
- Forward Voltage: R/Y 2.0-2.2V; B/G/W 3.0-3.2V
| Variant | Attachment or form | Switching | Weather or water information | Runtime information | Added complexity or tools |
|---|---|---|---|---|---|
| Throwie bugs | Multiple throwies linked into a chain; long chains may not stick as well. | Not stated by Make:. | Not stated by Make:. | Not stated by Make:. | Requires making and connecting multiple throwies; no special tools stated. |
| Indestructible LED Lantern | LED and CR2032 inside a PVC pipe cap and plug assembly. | Not stated by Make:. | Make: reports that its lantern survived a week submerged, freezing, and laundering. This is a report about that project, not a general durability rating. | Make: says the lanterns glow for days. | Uses a 10mm LED, PVC cap and plug, thread-sealing tape, and a binder clip; optional tools include a drill and 3/8-inch bit, drill vise, hot-glue gun, pliers, and wire cutters. |
| LED Jellies | Throwie adapted into a glowing jellyfish form. | Not stated by Make:. | Not stated by Make:. | Not stated by Make:. | Form-specific materials and tools are not stated in the project summary. |
| Floaties and Swimmies | Throwies without magnets placed in helium balloons or plastic fish toys. | Not stated by Make:. | The balloon and toy-fish forms alter how the lights are carried; no water-resistance rating is stated. | Not stated by Make:. | Requires a balloon or plastic fish toy; no specialized tools stated. |
| Programmable throwie | Retains the throwie form. | An ATtiny microcontroller can be added for Morse-code messages. | Not stated by Make:. | Not stated by Make:. | More electronics and programming work than the basic build; tools are not stated. |
| Motion-sensing version | Retains the throwie form. | A guitar-string intermittent switch creates flicker. | Not stated by Make:. | Not stated by Make:. | Adds a switch component; tools are not stated. |
Add a simple on/off control
For a basic switch, sandwich the LED’s longer lead between cardstock tabs. Arrange a sliding tab so moving it breaks or restores contact with the battery. This gives you a way to turn the LED off without rebuilding the taped assembly.
Make a more durable lantern
The Indestructible LED Lantern encloses a 10mm LED and CR2032 in a PVC pipe cap and plug assembly. Its materials include thread-sealing tape and a binder clip; the project also lists optional tools such as a drill with a 3/8-inch bit, a drill vise, hot-glue gun, pliers, and wire cutters. Make: reports that its lantern version survived a week submerged, freezing, and laundering, and glowed for days. Those are project-reported results for that build, not a guarantee that another lantern will withstand the same conditions.
Source and timing
Make:’s project page estimates 15–30 minutes for the project and gives a historical note of 25 disc magnets for about $13. The page dates to 2012 and was updated in 2015, so that price is not a current quote. Read the Make: LED throwies project.
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