It's not necessary to follow along with these steps, rather just read and take it in ready for the real soldering in the next stage. You can always refer back to this if you forget how to do anything.
Place the component into the PCB (Printed Circuit Board), making sure it goes in the correct way and it is sitting right against the board. Bend the legs to keep the component in position.
NB: Some components have a what is known as a "polarity" meaning current must flow through them in a certain direction. In the example presented here, we are attaching a resistor which doesn't have a polarity so can be inserted in any orientation. When we get to a component that has a polarity, I'll explain then in which orientation it needs to be inserted, but the only thing to be aware of now is just that some components do and some don't have a polarity so it's important to check before inserting them.
On the reverse of the PCB, place the soldering iron tip at the point on the PCB where the leg of the component meets the solder pad. Heat for about 3-4 seconds.
Pro Tip: As you add more components at can get difficult to hold the PCB flat while you solder. To help, try placing your PCB on some blue tack or similar in order to to keep the PCB stable.
Using your other hand, add solder to the heated pad. Add enough solder to cover the pad and the base of the components leg. Remove the solder and leave the iron for another second.
After soldering both legs, take your wire cutters and remove the excess component leg.
If you make a mistake, re-heat the join and use a solder sucker to remove the molten solder and start over.
Find the LED matrix PCB and orient it as pictured.
We’ll start by adding the machine pin headers that hold the LED matrix. This comes as one piece and needs to be cut into two. Find the header strip and cut it into 2 x 8 pin lengths using your wire cutters.
Place the two strips into the front of the PCB as shown and then carefully flip the part over taking care not to displace the pins. With everything located, solder the pins into place and check for alignment.
Pro Tip: Start by soldering a single pin and then flipping the PCB over to check for alignment. If the strip is leaning in either direction, carefully re-heat the solder and re-position the header strip until it sits perfectly vertical. Once aligned, go ahead and solder the rest of the pins. It’s much harder to re-align your headers once all pins have been soldered.
Next, take the 10uF electrolytic capacitor and place it into the holes marked C2 on the PCB. You may notice that the capacitor has one leg longer than the other. This signifies that the component has a polarity and so needs to go in your PCB a specific way around. The long leg is the positive leg and so needs to go into the hole marked with the little ‘+’ symbol. You’ll want to bend the legs 90 degrees so that the capacitor lies flat, rather than standing on it’s end as pictured.
Once located, flip the PCB over and solder the component into place and snip off the excess wire from the legs using your wire cutters.
Next, solder on the 0.1uF ceramic capacitor followed by the blue 10k resistor (assuming you didn't follow along with the Soldering 101 section, but if you did, then your 10k resistor should already be attached) into the C1 / R1 holes respectively. These parts do not have a specific polarity like the electrolytic capacitor does so the orientation of these parts is not important meaning they can just be placed into the PCB in any direction.
Next we’ll attached the MAX7219 IC (Integrated Circuit) LED matrix driver chip. Starting with the IC socket, locate it into the PCB taking care to align the notched end of the socket with the notched end of the graphic on the PCB. IC’s need to be attached in a specific orientation so this notch is used to help you identify the correct way to attach it. Once located, again flip over and solder into place.
With the IC socket soldered in, go ahead and press in the MX7219 IC into the socket, again taking care to align the notched end of the IC with the notched end of the IC socket.
NB: You may need to slightly bend in the legs of the IC in order to get it fit into the socket. Just take your time and be careful not to damage any of the legs.
The last thing to do with the LED matrix for now is to attach the LED matrix itself. To do this just push it into the machine headers we soldered in at the start, taking care to align all the legs into the headers. Again, this part needs to be oriented in a specific way which is the side with the writing on should be on the right hand side of your module.
Congratulations, you have now completed your LED matrix module. Place this to one side and move on to assembling the main the board.
NB: You may have noticed that you have a set of right angled header pins left over. Don't worry, you haven't missed anything, they just come as part of the LED matrix kit we are using, but we don't have a need for them in the Petduino kit so you can safely discard them, or better yet, save them for use in a future electronics project ;)
For the main board, we will be soldering components onto both sides of the PCB so it’s important to identify which side is the front and which is the back. The front side is the one with the large matrix graphic printed on, with the back being the side with the microcontroller graphic printed on.
With the board’s front facing you, solder in the 200ohm (band colours red, red, brown and gold) and 10kohm (band colours brown, black, orange and gold) resistors into R1 and R2 respectively, snipping off any excess wire as before.
NB: If the resistor colour codes mentioned above don’t match with the colours of your resistors, simply use a Resistor Code Calculator to find resistors of matching ohm values.
Next, attach the LDR (Light Dependent Resistor) sensor as pictured, taking care not to block the LED location, followed by the two right angled buttons.
Next, attach the red LED into the LED location on the PCB. LED’s are another component that have a polarity and so need to be placed in a specific orientation. Again, the long leg signifies the positive side with the short leg being the negative. Another way LED’s signify the polarity though is by having a slightly flattened edge to the LED. This flat edge will be on the negative leg. When placing the LED in the PCB then, make sure the flat edge of the LED lines up with the flat edge of the printed graphic on the PCB.
The last item to be soldered on to the front of the PCB is the LED matrix connector. Find the 5 pin male headers strip and solder this into place as pictured, taking care to make sure it sits perfectly vertically.
With the front side done (for now) flip the board over so that the back side is now facing you and start by adding the header strips for the microcontrolelr as pictured (we’ll attach the nano last so don’t attach it just yet).
Next, attach the temperature sensor and buzzer into their respective locations as pictured.
Carefully solder the microcontroller into place. This is one of the trickiest things to solder due to the small solder pads, so take your time and be careful not to damage the board. Hopefully at this point though you should have mastered your soldering iron and should be comfortable / competent enough to tackle this.
When you are done, you can cut the remainder of the header pins down with your wire cutters if you like, however this is not necessary.
The final bit of soldering we have left to do is to attach the LED matrix to the main board.
An important thing we want to avoid is shorting the LED matrix with any of the connections on the main board so to avoid this we will raise the LED matrix away from the main board. To do this, we will reuse the foam padding that the LED matrix came attached to.
On it’s own however, the foam pad is a little too thick, so to start with, carefully cut the foam pad in half as pictured and locate it on the main board.
Next, place the LED matrix on top of the foam pad, locating it on the LED matrix connector pins we soldered on earlier.
Next, and slightly tricky, solder the LED matrix to the LED matrix connector pins on the main board front, taking care to keep the LED matrix board perfectly parallel with the main board. We found the best way to achieve this is to solder a single pin first, then re-heat the solder and adjust the LED matrix position until everything is seated correctly, then let that solder joint cool to hold everything in place and then solder the remainder of the pins.
Congratulations, you have now completed soldering your Petduino.
Next, place onto each bolt 3 of the small green spacers as pictured.
Next, attach whichever accessory arm / ears you’d like to add to the top 2 bolts, and spacers onto the bottom 2 bolts followed by another spacer onto all 4 bolts. All 4 bolts should now have a stack of 5 items on them.
NB: If using ear accessories, you may wish to add these in the balk portion of the body, rather than the front half mentioned here. Feel free to play around with the location of your accessories as long as you have an even stack of spacers / accessories per bolt, you are free to use them in any combination you like.
Next, slide on the main board with the LED matrix facing down as pictured followed by 5 more spacers on each bolt.
Lastly, slide on the back plate followed by the nylon nuts tightening everything up using your screwdriver.
Congratulations, you have successfully assembled your Petduino.