Head & Eyes
First up is the LEDs for the eye that are mounted to the head of the robot. There's 2x LEDs (10mm and 3mm) that are wired together. The 10mm LED is mounted to the eye socket while the smaller 3mm LED is soldered behind the 10mm LED. The smaller 3mm LED illuminates the details in the head. A 220ohm resistor is used to limit the current and avoid burn out.
Prep 10mm LED
The two legs of the 10mm LED were bent to form a right angle using a pair of flat precision pliers. This will make it easier to mount to the eye socket on the robots head. Tin the legs with a bit of solder, near the upper area close to the LED bulb.
Prep 3mm LED
Now we'll need to prep the smaller 3mm LED. Trim the two legs short, but keep the anode (voltage) leg slightly shorter than the cathode (ground) leg. The longer leg on the 3mm LED is the anode (positive voltage). I used a pair of flush diagonal cutters to trim the legs short. Tin the shortened legs with a bit of solder.
Prep Resistor for LED
We'll use a 220ohm resistor to limit the current from the battery to prevent the LEDs from drawing too much current and burning out. Trim the two legs short and tin them with a bit of solder.
Wires for LED
We'll need two wires to connect to voltage and ground. I used 30AWG silicone cover stranded core wire for this. This wire has nice insulation and it's thin, flexible and yet durable. The two wires were about ~10cm in length. Make sure to strip the tips and tin them with solder. Tinning the tips of the wires will make it easier to connect them to the LEDs.
Connect 3mm to 10mm LED
The 3mm LED rests on top of the 10mm LED with the corresponding legs mating. Double check to ensure the correct legs are matching. Cathode to ground and voltage to anode. Add a bit of solder to the tip of the soldering iron and apply it to the mating legs for a secure connection.
Next, we need to attach a 220ohm resistor to the cathode (ground) leg of the 10mm LED. First, trim the two legs short but keep the anode (positive) leg slightly longer – this helps differentiate the two connections from each other. Hold the resistor over the cathode and apply heat to attach them together. Apply a small mount of solder to the tip of the soldering iron and add it to the connection.
Attach Wires to LEDs
Now it's time to solder the two wires to the LEDs. Attach one wire to the resistor that is soldered to the cathode of the LED. Then, attach the second wire to the anode of the LED.
With the wiring completed, we can then test out our LED circuit using a coin cell battery or equivalent. The resistor will limit the current from the battery and flow through both the 3mm and 10mm LED.
Mount LED to Head
Now it's time to attach the LED circuit to the head. Start by inserting the 10mm LED through the bottom of the head. Position the bulb behind the eye socket and firmly press inward until it's secured in place. If the LED doesn't fit inside the socket, you can use a filing tool to smooth out the edges and loosen up the tolerances. Test the LED circuit using a coin cell to ensure it wasn't damaged during the installation process.