Introduction: Sewable Surface Mount LEDs
Sewable LEDs are available from a few places but they come on a small piece of PCB which can be seen, especially when the LED is off. Depending on your application you might want something almost invisible - except when on of course. Using this method does however require a resistor in series with each LED (store bought sewable LEDs usually have a resistor soldered onto the board as well).
- Soldering Iron
- ~0.4mm (0.015") Soldering Iron Tip
- Wire Cutters
- Wire Strippers
- Small Pliers
- Sharp Anti-Magnetic Tweezers
- Small Block of Wood
- SM LEDs
- 22AWG Stranded Wire
- Double-Sided Sticky Tape
- Appropriate Valued Resistor
Step 1: Prepare the Materials
Cut a piece of tape as wide as your block of wood. Stick it to your block of wood and remove the protective backing (save this backing for later so you can cover the tape and use it again in the future). Stick an LED upside-down to the tape, using the tweezers if necessary, and then tin both contacts.
Strip a bit of the stranded wire and untwist it. Cut off about 2cm and use the pliers to bend a small foot one one end. Make the foot about the width of your LED, any longer and the wire will poke out the side.
Step 2: Solder and Test
Tin the foot of the lead before soldering it to the LED. Be sure not to use too much solder or burn your LED with your iron. 1 to 2 seconds of contact should allow the solder to flow around the lead for a strong join. A good test of strength is to remove the LED from the tape by pulling on the lead. If it comes off that means it wasn't strong enough!
You may want to check that your LED still works so grab an appropriate resistor and a voltage supply and give it a whirl. Use the following equation to find the proper resistance value
Resistance = (Supply_Voltage - LED_Forward_Voltage) / LED_Forward_Current
Step 3: Sew!
With the leads a millimetre or two apart poke them through the fabric you're using for your project. Remember which lead is the anode and the cathode as the marking on the bottom of the LED will no longer be visible. The flat side of the marking on the bottom of the LED is the anode while the pointy side is the cathode. Use pliers to twist the lead into little circles, the smaller the better. It's helpful to twist the anode (+) in a circle and the cathode (-) in a square so you don't forget which is which.
Now the LED can be sewn in with conductive thread. Once that's done it may be advisable to put a dab of hot glue on the back (encasing the leads a bit) to keep the leads from bending or breaking off.
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