Assembling the WEEDINATOR MCU PCB

Step by step video instructions on how to assemble the components onto the WEEDINATOR MCU PCB. 1. Initial SMD Population and Stenciling "Today we're going to populate the MCU PCB board. If we start on the top left corner, we got some surface mount voltage regulators. That's 5V, and then that one's 3.3. It's important to get the right component for 3.3 because there's several D2 pack components and some of them aren't wired rightly. Look over here, we've got an option for CAN bus, but we're not going to implement this today. Down here, we have some regular 0603 LEDs and an SBUS circuit. In here, we have some voltage dividers, which is really useful. They use 0603 resistors. There is also a buzzer, which is quite useful for commissioning the system and generally debugging, as are the LEDs. I suppose the buzzer and LEDs are optional, but I find them incredibly useful. This PCB is made by PCBWay. I've got another one here made by a competitor and it's actually got a tiny little fault—this pin is filled with solder. It shows you get what you pay for. If you want reliable quality, pay a little bit more. We’ll use a microscope to line up this fantastic stencil to make sure the surface mount components are exactly right. Before we get too carried away, we need to clean the stencil. If the paste goes hard on it, it's an absolute nightmare, so I’m going to use some isopropyl and give that a quick wash." 2. Component Identification and Reflow Preparation "These next resistors are 10k and 1k; you definitely don't want to get those mixed up. Fortunately, the 1k has a big fat zero on it, so it's easy to identify. I can’t really read the writing on the other without a microscope. Now for the LEDs: they have tiny little green marks on them, and the green always indicates the cathode. I’ll put the buzzer on now. Make sure the buzzer's the right way around—it has a positive mark, but you can use a multimeter to test the orientation. On this board, the writing on the PCB matches the orientation of the writing on the buzzer. Here's the 5V regulator and the 3.3V one. You might notice the middle pin isn't connected to the PCB; it doesn't matter because the ground tab at the back is the most important part and the pad connects to that pin anyway. We also have black crescent capacitors to ensure a stable voltage supply. I've checked everything with a magnifying glass and we are ready for the reflow oven." 3. Through-Hole Soldering and MCU Headers "Now we start the through-hole components. First is the ZX450 NPN transistor used for inverting the SBUS signal. The orientation is given by the graphics on the PCB, so it's impossible to get it wrong. Next are the male/female headers. We need to bear in mind the orientation of the MCU board underneath. It’s possible to get these headers at the wrong angle, which makes it really difficult. To avoid this, I solder only the ends first and then make sure the MCU slides on properly. We don’t want to force the MCU onto the board; I’ve actually cracked a chip before doing that. If they are wonky, I can feel it with my fingers underneath and adjust the heat until they click into place. Do not try to fully attach the MCU until the headers are completely soldered." 4. Fitting the MCU and Terminal Blocks "I’m going to use a broken MCU to practice the fit. Copious quantities of WD-40 are required here—it makes a massive difference in getting these things on and off without stress. When removing it, use a screwdriver to gingerly prize it off so you don't 'banana shape' the board. Next, we have the WAGO connectors—about 350 individual ones. You can bolt the sections together by removing the ends. Again, I only solder the ends first to check if they are wonky. In the past, I’ve made the mistake of soldering them all and finding they aren't seated properly. These orange ones are so much better than screw connectors, which are an absolute disaster in comparison. If they are out of position, I shunt them back with my finger while heating the solder." 5. Final Connections and Testing "Finally, I’m soldering the ground connectors—you can’t have too many grounds. I'm also adding headers for the GPS daughterboard, which houses two Ublox Series 9 units to give us heading data. Before we finish, there are two jumpers to remove, SB57 and SB31, to allow the use of PA1 and PA7 instead of the Ethernet pins. To test, I’ve preloaded some code. When I connect it, it should beep and flash the LEDs. There she goes! I also tested the regulators with a meter to ensure we have 5V and 3.3V. The rest will be tested once it's installed in a proper robot." Sponsored by PCBWay - the best quality and most reliable: https://www.pcbway.com/ . Other manufacturers exist, but we had quality issues with some of them.