4) LEDs

Surface mount resistors and LEDs

LED circuit

Order the PCB circuits online at PCB-Pool, using the Eagle file provided. 

Soldering station


Prepare the soldering station with a microscope, soldering iron with a thin tip, and solder. Ensure you are using an extractor, and have white-tack to hand for fixing the circuit while soldering.

Apply flux to the circuit (side with the mounting pads). Choose one of the 6 series of 4 pads, and deposit a small amount of solder on the left-most of the 4 pads as shown.
Applying flux
Using a pair of tweezers, hold the resistor on the solder and apply heat using the soldering iron to attach it. Apply solder to the unattached side of the resistor.  
Solder Resistor part 2 Solder Resistor part 2
Soldered resistor The soldered resistor should now look like this. 
Next, we will solder the LED, which has directionality. On the top of the LED, a small circle indicates the cathode (negative side). Thus for our circuit, the circle should be on the pad furthest from the resistor. 
Heat the solder on the pad nearest the resistor, and using tweezers as before, solder the LED to the circuit on its anode.  Solder the cathode to the pad furthest away from the resistor to finish the job. 
Solder LED part 1

Check that the LED and resistors are connected as shown. If the solder appears grainy, reapply flux and apply heat with the soldering iron.Then repeat the above steps for the other 5 resistors and LEDs.


Strip cables Strip both ends off 25cm length power and ground cables. 
Solder power cable to the through hole which connects to the inside ring on the circuit. Solder power cable to the through hole which connects to the inside ring on the circuit.
Solder power cable Solder ground cable
Cut the ends off both wires. Place the LED circuit on the 3d-printed body as shown.
Cut cable ends LED circuit in place
Cut the end of the USB extension cable and the protruding green and white cables. Leave the red and black cables, these corresponding to power and ground, respectively, and will power the LED circuit.  Strip the power and ground wires from the USB cable.
USB cable cut Strip USB cable wires
 Cut a small length of heat shrink for each cable, and feed the LED circuit wires through it. Solder the LED circuit wires to the corresponding power and ground wires from the USB cable.  To solder the wires together, first apply some solder to each wire individually.
Apply solder to first wire
 Then fix one cable, bring the other cable next to it and apply heat briefly with the soldering iron to solder the wires together. Using the heat gun, cover the connections with heat shrink.
Solder wires together Heat gun on heat shrink
Completed LED circuit The LED circuit is now completed. Plug in the USB cable to a computer and ensure that all 6 LEDs light up.