assemble the electronics


If you have your PCB in-hand and components together, it’s time to start soldering! There are a lot of solder points, but the soldering is very simple, as you are about to see. Click on any picture to see a bigger version. Note that the yellow/tan PCBs pictured below were made on a CNC router and the blue PCBs are the professionally manufactured version.


Insert the NodeMCU ESP8266-12E development board into the PCB. It’s possible to accidentally install this board backwards, and it’s difficult to remove once it has been soldered, so make sure that you have the pins oriented correctly. Solder all of the pads that have traces. There are 12 in total – ten in one row of pins and two in the other. You do not need to solder the copper pads that do not have traces. If you have a difficult time getting solder to flow around these pins, rosin paste flux will help.


Assemble the 5V voltage regulator and heat sync as shown, then solder its three leads to the PCB to the left of the NodeMCU 8266-12E development board as seen in the photos.


Install the two capacitors into the pads that are immediately behind the voltage regulator. Pay attention to the order and polarity of the capacitors. The 100µf capacitor needs to be installed closest to the outside edge of the PCB, and the 10µf capacitor will be installed closest to the inside of the PCB. The negative leads of the capacitors should be facing each other.


Solder all eight MOSFETs into the PCB in the pads that are to the right of the NodeMCU development board. When you solder the bottom layer, it is only necessary to solder the leads that have traces. However, there are twenty four leads, and eighteen of them need to be soldered on the bottom side of the PCB, so it helps to avoid confusion if you take a couple extra minutes and solder all of them. You can also avoid having to solder the top layer by flowing solder through the appropriate vias, as described below.


Solder the board’s top traces

If you have a double-sided PCB, solder the eight solder points that are connected to traces on the top side of the PCB. Those traces are connected to each of the eight right-side legs of the MOSFETs. An easy way to solder the top-side connections is to heat the pins a little from the bottom-side with your soldering iron, then  use a little rosin paste flux and apply enough solder from the bottom to allow it to flow through the via. This method will work without rosin paste flux, but the flux will help the solder flow a little more freely and with less heat. When you remove the heat, you should have a solid solder on the top of the board. Be sure to test your work!

If you do not have a double-sided PCB, you will need to connect the right-side leg of each of the MOSFETs to each other. This is a ground connection in the circuit. The lower-left MOSFET in each group of four is already connected to the circuit’s common ground on the bottom side of the PCB, so it is sufficient to connect the right-side leg of the other three MOSFETs in that same group to its ground leg. You can do this by soldering jumper wires directly to the legs of the MOSFETs on the top side of the board, or by soldering jumper wires to the appropriate leads on the bottom of the PCB. I chose to solder on the bottom of the PCB so that I could conceal the wires within the case.


Install the two-pole, 5mm pitch screw-down terminal on the left side of the NodeMCU development board. Screw-down terminals take quite a lot of abuse, so secure it to the PCB by adding a drop of super glue and pressing it in place against the PCB for 30 seconds. Once it is glued into place, solder its two leads on the bottom of the PCB.


Install the (2) five-pole, 3mm pitch screw-down terminals on the right side of the MOSFETs. Glue these terminal blocks to the PCB in the same way as instructed above, then solder all ten leads on the bottom of the board – five leads for each terminal block. Alternatively, you may use (2) two-pole terminal blocks and (2) three-pole terminal blocks. Two and three-pole terminal blocks tend to have a smaller profile, which you may prefer.


Everything is soldered, so it’s time to clean up and verify your work. Start by putting on safety glasses, then trimming the excess metal from the leads on the bottom side of the board. I recommend NOT trimming the leads of the NodeMCU ESP8266-12E development board. The pins are very thick and tend to damage wire cutters.

Verify your work by testing the trace end-points with an ohmmeter. Simply connect one lead from your ohmmeter to a solder point on the PCB, then connect the other lead to the solder point that is on the other side of the trace. You should have continuity between all appropriate traces. It is an especially good idea to double-check your top-side solder points. To do so, connect one lead of your ohmmeter to a ground pin on the NodeMCU ESP8266-12E development board, then connect the other lead to the right-side leg of each of the MOSFETs, one at a time. There should be continuity between those pins and the circuit’s common ground.