Welcome to LE STRUM! This is a pretty packed little board, but it should not take too long to make up (a couple of hours if you are new to soldering). Beware that some of the components we’ll use are fussy about being soldered the right way round, others are not, but I will let you know as we go.
OK, First lets get familiar with the PCB.. this is the top side
This is the bottom side. In general we’ll be doing all our soldering on the bottom side of the board, and the components will sit on the top side.
When soldering a PCB, it generally helps to solder lower height components first. This stops the taller components getting in the way while we are working, and it lets us hold components in place for soldering by turning the board upside down on a flat surface and letting gravity be our third hand!
Let’s start by soldering resistors R1, and R2. These are 220 ohm resistors which have a colour code of red-red-brown. Lets start by bending the legs as shown
Pass the legs of the two resistors through the holes in the board marked R1 and R2 as shown (Resistors do not have a specific polarity and can be soldered “either way round”).
Push the resistor flush to the board and bend the legs out slightly to hold it in place while you turn the board over to solder them.
Now… some soldering advice. If you are a dab hand at this kind of stuff you can skip this bit :)
Before you start soldering, make sure the tip of your iron is clean and up to temperature. Melt a little solder on to the tip to “tin” it. Use a soldering sponge or wire wool tip cleaner to remove excess solder leaving a thin bright silvery coating on the tip.
Bring the tip of the iron to where the leg of the resistor emerges from the hole and, at the same time, bring the end of your solder wire to where the iron tip,resistor leg, and PCB hole all meet each other. Don’t melt the solder directly on to the tip of the iron but rather melt it at the point where the iron tip touches the component leg. This should not longer than about 2-3 seconds. After applying the solder, remove the solder wire and continue to apply heat to the joint for about 1 second. You should see that the molten solder gets “sucked” into the plated PCB hole, forming a good connection. Now remove heat and allow the joint to cool naturally for a few seconds (don’t blow on it). The final joint should be bright and shiny, not dull or grey.
Use your wire wool tip cleaner or sponge to keep the tip of the iron clean. Clean excess solder from the tip every time you make a solder joint and re-tin it frequently. A clean, well tinned tip is the key to making good consistent solder joints.
Here is what I ended up with
Once soldered, cut the legs nice and short. Take care not to damage the solder joint when cutting away the excess component leg wire
The result should look something like this. The resistors are flush to the board with no kinks in the legs, and a little solder has been drawn through the holes forming a little solder joint on the top side too
Now, repeat the process with the other resistors.
* R4, R8 - 1 kOhm (brown-black-red code) resistor
* R3, R5, R6, R7 - 10 kOhm (brown-black-orange code ) resistor
The board should now look something like this
Now lets add the 1N4148 small signal diodes (all sixteen of them!).
Unlike resistors, diodes DO have a polarity and need to be soldered a specific way around. Both the diode and the symbol representing its location on the PCB show a thick line marking one end of the diode (the Cathode)
The diodes have a tiny orange and black glass package. There is a black stripe on the cathode end which aligns with the stripe shown on the diode symbol on the board. Solder the diodes as you have resistors. Please note that diodes are a bit more heat sensitive than resistors - so don’t cook them too long with the iron.
Next we’ll solder the power switch. I recommend placing it in its holes and turning the board upside down on a flat surface so that the weight of the board holds the switch in place while we solder it. Solder just the middle pin, turn the board back over and ensure the switch is flush to the board and parallel to the edge (if not, re-heat the joint while pressing the switch down to the board). Finally solder the remaining 2 pins and trim the legs
Now add rectifier diode D1
Lets got on and solder some switches… we have a lot of these to get through (Thirty-seven!). Start by placing the top row of switches into their holes as shown. Press them firmly down to the board.
Turn the board over and place on a level surface so that the switches are pushed flat to the board. Solder JUST TWO CORNER PINS of each switch to begin with. This will let us adjust the position if we find any are crooked.
Hold up the board to check along the line of switches, making sure they are all straight and levelled to the board. If any are out of alignment, reheat the solder joints and adjust them.
Finally solder the remaining two pins of each switch in the first row.
Do the same for the second and third rows of switches, taking care to keep them aligned and flat to the board.
Solder the five 100nF ceramic capacitors (C1, C2, C3, C4, C7) and the “mode” switch (S27). Your board should now look like this
Now we will solder on the LEDs. These parts have a polarity (meaning that they only work one way around) so we need to be careful to get this right. On each LED the LONG leg is the (+) terminal, called the ANODE. The shorter leg is the (-) terminal, called the CATHODE. The cathode is also marked with a “flat” on the edge of the domed lens, although this can sometimes be difficult to see.
Locate the holes for the LEDs. The symbol on the board marks the (-) cathode flat edge. Please see the photo below for the polarity of each LED, noting that they are they are located the opposite way around to each other (one has + on the top, the other has + on the bottom). I recommend using the red LED for steady power indicator and the brighter blue LED (with the white lens) for the flashing activity indicator.
The soldered LEDs should be nice and flush to the board as shown below
Next we will deal with the two electrolytic capacitors (C5, C6). These are also polarised components and there are indicators to tell us which lead is which… once again the ANODE (+) is the longer leg. These capacitors also have a white stripe on the case which indicates the CATHODE (-) leg
The board clearly indicates the ANODE hole with a (+) symbol
When the capacitors are soldered they should look like this…
Next we will add the sockets for the integrated circuits (ICs). Your kit contains two sockets with 16 legs and one with 14 legs. Be careful not to accidentally solder the 14 pin socket into a 16 pin hole! The sockets have a “notch” in one end (marking “pin 1”) and a similar indicator is printed on the circuit board as shown below
When inserting the sockets into the holes on the board make sure you align the notch on the socket with the notch marked on the PCB symbol. I recommend soldering the sockets one at a time; insert the socket in the holes, invert the board and solder just two corner pins. Ensure the socket is flat on the board before soldering the remaining pins
Next to add is the voltage regulator (REG1). This is a small black component with a D-shaped case and three legs. There is a correspondingly marked location for it on the PCB.
Ensure the D-shape of the can is aligned with the symbol on the board. You may need to bend the middle leg back slightly to fit it through the hold on the board. The regulator will sit a couple of mm above the board surface when soldered as shown below
The MIDI socket should fit easily into the location for it on the board. Turn the board upside down and solder just 2 pins of the socket. Make sure it is flush to the board before soldering the remaining pins. The socket needs to be completely flush to give it mechanical strength as cables are plugged and unplugged.
Now our board should look a bit like this
Lets get the bits together for the stylus
Strip about 1.5cm of insulation from the wire and twist the wire strands tightly together
Insert the wire through the hole in the 4mm connector pole and wrap it back around to get a good mechanical connection
Soldering the wire to the connector can be a challenge, since the connector is large and rapidly conducts the heat from the soldering iron tip away, so we can end up with solder blobs on the wire that are not attached to the connector. The way to do this is to get the connector really HOT. Make sure its on a heatproof surface and push the iron against the joint between the stranded wire and the connector, leave it there for 10-20 seconds until solder will happily melt at the interface and spread between the connector pin and the wire. Allow a decent amount of solder to form the joint then let the pin cool for several minutes (it might be small but has the heat capacity to REALLY burn your fingers if you pick it up when its still hot)
When cool, align the wire with the pin
Push the pin into the plastic holder
Close up the little door and push the pin back a mm or so into the circular hole to lock the door in place
Now strip back about 1cm of insulation from the other end of the wire, twist the strands together, tin them lightly with solder and trim back to about 0.5cm
Insert the wire through the stylus hole and solder from the back, trimming the excess wire
The next step is to add the battery holder. This fits to the rear of the board and does not quite fit flush to the back of the board due to the solder joints (but whats a mm between friends?) but we can improve matters by making sure we trim the solder joints nice and close in the marked area where the battery holder will be attached. Pass the legs of the battery holder through the holes in the PCB and loosely attach the screw (I only use a single screw to attach the battery holder in this project, in addition to the solder joints). Solder the connections and tighten the screw. Trim the solder joints.
Now we should have something a little like this
Now lets insert the IC’s into their sockets. Take care to align the notches in the IC case with the notch in the socket. This ensures we have our pin 1 in the correct location. Attach the four hex standoff pillars (short ones on the front edge, longer ones on the back) using the machine screws… and finally we’re done!