Step 3 - Surface Mount Parts

You should have four strips of surface mount parts. Put the clear strip to one side, you will solder that later. There are spares on each strip, you can use them if necessary.

You should now have three strips of resistors. There is some very small lettering on all of them showing the value. You may need a microscope or other optical enlargement device to read them.

(Note - you may have a different way of soldering resistors than the one described below, TL;DR just solder the resistor values shown in the table below to the locations also below.)

Conversion Table

Marking

Location

Value

470

R2, R3

47 ohm

121

R1

120 ohm

0

R4, R5

0 ohm Link

If you can, switch to a fine soldering iron tip now, it will make the soldering ahead much easier.

Flow solder onto just one of the pads for all the part locations detailed above (each location is labelled with both the value of resistor to be placed there and it’s identifier in white lettering on the board.) An example is below.

Follow these steps for all three strips. First, remove the plastic cover from the top of the strip, use tweezers if you cannot do it by hand. Being careful not to accidentally inhale the resistors, pick one up with tweezers and place it on the board location shown in the table above. Hold it in place and reflow the pad you have already applied solder to. After making sure the part is securely in place, continue to solder the other side in place. If necessary, touch up the side you soldered originally and ensure both pads have a nice smooth, shiny joint. An image of a perfect resistor is below.

_images/smd_perfect.jpg

A perfectly soldered resistor

If you make a mistake soldering a resistor (and you most likely will) or simply lose one, we’ve included at least one spare. If necessary, you can desolder a resistor by applying upwards pressure with tweezers while heating both sides.

Now for the power LED. Retrieve the clear strip from earlier and extract the LEDs from it. Identify the side with the green arrows. Position the LED on the board with that side facing towards the vertical line, as shown in the image below.

_images/led_pos.jpg

Solder the LED using the same process as you did for the resistor and bridge the two contacts to the left to enable it. You can break this connection when you have verified the kit works as intended to disable the LED and increase battery life.

If you are unsure, please refer to the video below:


Troubleshooting

  • If you have any, apply flux to all pads before soldering. This will clean off oxides that have formed since the boards were manufactured.

  • Avoid lead-free solder, both in general for hand soldering and especially so for SMD soldering. Use a high quality 60/40 solder with a rosin flux core for best results.

  • If you have issues later on, the resistors are most likely the culprit, if a specific colour on an LED doesn’t work or some LEDs don’t work altogether reflow all the joints on your resistors and make sure they are flush with the board and in the right location.