Have you seen my GPIO Xmas Tree for the Raspberry Pi? If so, you may have noticed that, like most modern circuit boards, it uses “surface mount” components where the components are soldered to the surface of the board rather than having legs that pass through the board.
Do you fancy trying some surface mount soldering yourself? Believe it or not, it is possible with a normal soldering iron and a pair of tweezers! This kit has been designed for you to try soldering your own GPIO Xmas Tree. You will get a panel of 3 trees in the hope that you will get at least one of them to work. Maybe all three will work!
Find out how to buy the kit by clicking here.
Please note, however, that this kit isn’t really suitable for beginner solderers. It’s for people who are reasonably experienced at soldering and feel comfortable with soldering traditional “through hole” components.
1. Watch a demonstration
First, watch the first three minutes of this Collin’s Lab video that shows the basic idea of how to solder resistors and LEDs i.e. put a small amount of solder on one pad, re-melt the solder and slide the resistor into place with tweezers, then solder the other pad. Soldering an LED is very similar but LEDs must be soldered the correct way round (more on this later).
You see another demonstration by John Gammell here.
If you read the YouTube comments then you will see lots of people saying “you should be using flux!” but don’t let that worry you too much for a hobby project.
2. Get the gear
For this kit, you will need:
- A soldering iron with a fairly fine/pointed tip + stand + tip cleaner/damp sponge
- Solder – the thinner, the better (e.g. 0.7mm)
The following may also be useful:
- magnifying glass
- a blob of Blu-Tak or some tape
- 2 x AAA batteries
- Raspberry Pi
3. Practise soldering resistors
Hint: do not remove all the resistors at once from the packaging. If you have a pile of resistors on your desk and are unfortunate enough to sneeze then they will scatter everywhere!
If you look on the side of the board then you will see it says “Practise soldering resistors here”. In these photos I have already snapped the trees out of the panel but that’s not necessary:
Use the technique shown in the videos above, namely:
- put a small blob of solder on one pad
- bring the resistor nearly into place using the tweezers
- use the soldering iron to re-melt the solder and push the resistor in place with the tweezers
- solder the other pad
- you can then go back and re-solder the first pad if necessary.
Remember: not too much solder! You can always add more solder later if needed.
As you solder the resistors, you can test your work by connecting a multimeter to the two circular test points either side of the resistors. If all is well, the resistance should measure around 330 ohms:
4. Practise soldering the LEDs.
Solder all three resistors before tackling any of the LEDs:
IMPORTANT: you must solder LEDs the correct way round or they won’t work. If you look on the reverse of the supplied LEDs then you will see that they are marked with a green T shape:
The T-shape needs to point in the same direction as the marking shown on the circuit board:
Solder one LED in place. You can check it works by briefly touching the red and black wires from the AAA battery holder onto these two pads:
If all is well, your LED should light up:
If the LED does not light-up, try reversing the black and red wires… if that causes the LED to illuminate then you soldered the LED the wrong way round!
If you solder two LEDs successfully then you could leave the third unsoldered and use the unsoldered pads as an LED tester for surface-mount LEDs.
5. Onto the trees!
Now that you’ve practised soldering resistors and LEDs, it’s time to take a deep breath and move onto the trees. I strongly suggest that you build only one tree initially and see if it works before progressing onto the next tree. There are three trees in the kit and it might be reasonable to assume that you get only one working tree if this is your first time with this type of soldering. But maybe you’ll be lucky and get 2 or 3 working trees.
The resistors and LEDs should be arranged like this:
I would suggest soldering the resistors first. When soldering the LEDs, take a look at the back of the board and notice that a T shape is marked to show the correct orientation of the LEDs. The “prong” of the T should point towards the top of the tree:
6. Solder the connector
Snap your soldered tree out of the panel and use some sandpaper to tidy-up the “mouse bites” (don’t inhale the dust).
Now for the trickiest part of the whole operation: soldering the connector onto the 6 pads at the rear of the tree. It can be difficult keeping it all aligned but Blu-Tak or taping the tree to a table can help here:
Solder just one pin initially:
Check that you are happy with the alignment of the connector and then solder the remaining pins.
7. Testing the tree.
You have two options here, either you can connect it straight to the Raspberry Pi as detailed here or you can solder the switch, header pins and battery pack to the frame.
If you solder the header pins then you can attach three trees like this:
Finally, if you are using the frame as a display stand, attach the four rubber feet to the underside of the base.
If you’ve enjoyed this kit and had some success, please do tweet me a picture!
There is a more advanced technique called “reflow soldering”. It’s not as practical as the above method for hobbyists but you can find out more on the Sparkfun page.