What you need:
- One learn to solder LED necklace kit
- One soldering iron
- Solder with flux
Accessories (not necessary for this project but useful for future soldering work)
This project should not be completed without adult supervision!
- Soldering irons get very hot and can cause burns! Be very careful not to touch the tip of the soldering iron while you are working.
- Although lead-free solders are available, most high quality solders still contain lead. Make sure you wash your hands after working with leaded solder.
- Wear safety glasses to protect your eyes.
- Do not eat or drink while soldering.
- Printed Circuit Board (PCB) – printed circuit boards are stiff laminate boards that have circuits printed on them.
- Solder – electrical solder is made of metals that are conductive and melt at low temperatures. When the solder is heated with a soldering iron it melts and can be easily applied to your electrical connections. When it cools, it solidifies forming a permanent electrical connection. If it helps, you can think of it as conductive hot glue for circuits.
Prepare the soldering iron:
- Turn on your soldering iron and wait for it to warm up.
- Wet the sponge you are working with
- Once the soldering iron is warm, clean the tip by wiping it on the wet sponge. This should remove any old solder. If this is not effective, melt additional solder onto the tip and try cleaning it again.
- “Tin” the tip by melting a thin layer of fresh solder onto the clean tip.
Step One: Solder the battery holder to the back of the PCB (printed circuit board)
-> If you purchased the kit, this step has been completed for you. It is still recommended you read this step for educational purposes.
This kit comes with a surface mount battery holder. “Surface mount” parts have leads (the metal “wings” on the holder that attach to the board) that are mounted directly to the pads on the surface of the PCB without using through holes.
To mount the battery holder:
- Touch the tip of the soldering iron to one of the bond pads on the board
- Hold the tip of the solder to the board so that the end is touching both the tip of the soldering iron and the bond pad on the board
- Apply a small mound of solder to each of the pads
- Place the battery holder onto the PCB so that the leads are covering the bond pads (as shown below)
- Hold the tip of the soldering iron against the top of one of the battery holder leads. When the solder below the lead starts melting, press against the lead with the soldering iron until it is flush with (flat against) the board.
- Repeat on the other side.
This step isn’t too difficult but if it isn’t done right the battery holder can easily be ripped off of the board when the battery is inserted. For this reason, the PCBs in this kit come with the battery holders pre-populated (already attached). If you feel confident in your soldering abilities, you can request a kit without the battery holder soldered to the board.
Step Two: Attaching your first LED
The important thing to know is that LEDs (Light Emitting Diodes) are directional which means that the current can only flow through them in one direction. So it is important to know which are the positive leads and which are the negative leads on the LED. The best way to determine the polarity of the leads is to look at their length. The positive lead is always longer than the negative lead (as shown in the diagram below).
For this kit all of the positive leads are oriented towards the outside of the circle. Unfortunately, this information was accidentally deleted from the solder mask in the Rev 1A version of these boards. This will be updated before the next batch of boards are ordered!
As you can see from the diagram all of the positive leads (red) of the LEDs are connected to the positive leads on the battery holder and the negative leads (black) of the LEDs are connected to the negative battery contact pad on the PCB.
So this board is just a printed version of a very simple circuit with eight LEDs connected in parrallel to a coin cell battery!
Now that you understand the board layout you can go ahead and attach your first LED:
- Take your LED and feed the positive (longer) lead through the the LED hole closer to the outside of the circuit board and feed the negative (shorter) lead through the hole closer to the center of the circuit board. The LED bulb should be on the front side of the board with the leads poking through to the back.
- Clean and tin the tip of the soldering iron if you have not already done so.
- Place the tip of the soldering iron against one of the LED leads. Then touch the solder to the lead on the opposite side of where the soldering iron is touching the tip.
- Wait for the solder to melt. Coat the base of the lead with solder. Try to create a small clean mound of solder at the base.
- Repeat eight times until all of the LEDs are connected to the board
Step Three: Insert the battery
- Insert the battery into the battery holder. All of your lights should light up!!
- If some of your LEDs are not on, double check the solder in that area. Make sure there is enough solder to connect the LED to the board and that there isn’t so much solder that the positive and negative leads are connected.
Step Four: Trim the leads
- Use a wire cutter to trim the LED leads.
Step Five: Cover the back with felt
- Place the square of adhesive felt on the back of your LED necklace
- Trim away the extra material until you can’t see the felt when you look at the front of the necklace
Step Six: Add the lanyard
- Attach the lanyard or your chain of choice to the necklace
Step Seven: Wear it!
Step Eight: Share it!
- Congratulations, you now know how to solder!! Show your new skills to your friends and let them know how much fun working with electronics can be!
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