The Tool Desk
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What you need
- One LED
- One 3V CR2032 coin cell
- 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.
- Place the LED leads on opposite battery terminals. Put the LED’s longer lead against the positive face and its other lead against the opposite face. The LED should light when both leads make contact and the polarity is correct. This simple build is described by West Florida Components and SparkFun.
- Attach the magnet. Position the disc magnet against the battery.
- Secure the assembly. Wrap electrical tape around the battery, LED leads and magnet so the components stay together. Do not assume the taped assembly is weatherproof or child-resistant.
If the LED does not light
- Check that the two LED leads touch opposite battery terminals rather than the same face.
- Confirm the longer lead is on the battery’s positive face.
- Make sure the leads maintain contact while you secure the parts with tape.
Does a basic throwie need a resistor?
For this particular simple circuit, SparkFun describes connecting the LED directly to a coin cell; the cell’s limited current prevents damage to the LED in that setup. That does not mean an LED can be connected directly to any battery. Adafruit notes that direct drive puts strain on a coin cell and can shorten its run time. A resistor may improve longevity, but its value depends on the LED and power supply. In a modified circuit, the LED and correctly selected resistor are connected in series; do not assume one resistor value suits every combination. See Adafruit’s coin-cell LED guidance and SparkFun’s LED circuit guide.
Use and dispose of throwies responsibly
Use a throwie only on an appropriate metal surface where placement is permitted, and retrieve it afterward. Do not toss or leave one on a bridge, building, or other public structure: discarded batteries and electronics become litter and e-waste. Adafruit advises against leaving throwies on public structures.
Coin cells are dangerous if swallowed. The U.S. Consumer Product Safety Commission warns that a swallowed button or coin battery can burn through a child’s throat or esophagus in as little as two hours. Keep new, used and assembled cells inaccessible to children, and do not leave loose batteries where they can be reached. The throwie’s tape does not make it child-safe.
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- 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
For a discharged battery, the CPSC advises putting nonconductive tape over its terminals or around the battery and taking it to a battery-collection center. Follow local battery collection guidance. If ingestion is suspected, seek medical attention immediately; the CPSC lists the National Battery Ingestion Hotline at 800-498-8666 and Poison Help Line at 800-222-1222. Consult the CPSC button cell and coin battery safety information.
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