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An LED throwie is a simple assembly of a 3V CR2032 coin cell, an LED, a small disc magnet, and tape. Put the LED’s longer lead on the battery’s positive face, place its other lead against the opposite face, then tape the magnet and parts together. Use the device only on a permitted metal surface and retrieve it afterward.
What you need
- One 3V CR2032 coin cell
- One LED
- One small disc magnet
- Electrical tape
How to make an LED throwie
- Identify the battery’s positive face. Check the markings on the CR2032 so you know which side is positive.
- Position the LED. Put its longer lead against the battery’s positive face. Place the other lead against the opposite face. The LED lights when its leads make contact with the two different battery terminals.
- Attach the magnet. Place the disc magnet against the battery.
- Wrap the assembly. Use electrical tape to hold the parts together, covering the magnet so it stays attached.
If the LED does not light
- Check that the longer LED lead is on the battery’s positive face.
- Make sure the two LED leads touch opposite battery terminals, rather than the same side.
- Check that both leads are making contact with the battery.
Does an LED throwie need a resistor?
For this basic CR2032 throwie, the LED can be connected directly across the coin cell. SparkFun explains that the cell’s available current is limited enough to prevent damage to the LED in this simple setup. However, direct drive stresses the coin cell and can shorten its run time. SparkFun’s LED guide and Adafruit’s LED sequin guide describe the direct-drive trade-off.
If you modify the circuit, use a resistor in series with the LED and choose its value for the specific LED and power supply. There is no single resistor value that is right for every combination; SparkFun’s guide explains the factors involved.
Coin-cell safety, placement, and disposal
Button and coin cells are dangerous if swallowed. The U.S. Consumer Product Safety Commission warns that a swallowed cell can burn through a child’s throat or esophagus in as little as two hours. Keep loose cells and completed throwies inaccessible to children, and secure loose-cell terminals. The device described here does not enclose the battery in a child-resistant compartment.
#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
If ingestion is suspected, seek immediate medical attention. The CPSC lists the National Battery Ingestion Hotline at 800-498-8666 and the Poison Help Line at 800-222-1222. For a discharged battery, the CPSC advises putting nonconductive tape over the terminals or around the battery and taking it to a battery-collection center. Follow your local battery collection and disposal guidance. CPSC button-cell and coin-battery safety information.
Place a throwie only on an appropriate metal surface where you have permission, and retrieve it afterward. Do not toss it onto a bridge, building, or public structure: a device left behind becomes litter and electronic waste. Adafruit advises against leaving throwies on public structures.
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