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Ben’s got his hands on the Hex Game PCBs he sent for from Osh Park. Now, he’s going to solder it up to make sure everything works. In theory this is the same as the laser paint version they made. He also needs to program a few things differently. Instead of having two switches for game free play hex binary, he just has one button for select. This was designed for the ATTiny25, so they could use a pin-compatible 45 or 85 if they run out of program space. Also, there is a fourth digit now so he’s thinking that they could use that for status display or have a heck H or a B to tell you what mode you’re in. Next they’ll have Karen and Max solder, as they less experience then Ben and Felix, and use that as a barometer to see if this would make a good teaching kit for students.
The NOT gate is a little small but that can be removed. There are still a good number of through-hole components on the board, including the toggle switches which need the holes for strength. Ben gives some surface mount soldering tips as he goes along. He points out the SOIC-16 package and one of the output shift registers that will drive the display. He adds a bit of solder on one of the corner pads, brings the chip over, heats up the pad, and then slides it into position. He ensures that the pins are not overlapping so that it’s straight enough. To ensure that it’s locked in position he solders the opposite end. Once those two are in place he can just go in and hit the rest. Soldering is about heating up the piece with your iron and then bringing the solder in. You can also do a flood fill.
The surface tension of the solder pulls it away from each pin. You don’t necessarily have to get every pin with a surface mount, you just have to get solder on everything and make sure there’s nothing short circuiting. The surface tension works with the solder on the iron as well. After fixing a mistake, Ben solders on some surface mount resistors. Like the IC, the first bit of solder acts as an anchor to keep the part straight. Even heat transferred on the copper PCB can cause nearby parts to slide off. Next, Ben demonstrates his method for soldering on some surface mount PNP transistors. Having a finer tip on a soldering iron will give you more accuracy but transfer less heat.
Ben gives some tips for soldering on through hole components. He ensures that he’s heating up the pad and the pin to get a good solder bond. You have to flow the heat through both items and the solder will follow along. The notch gives you more surface area with which to transfer heat. Before putting in the 5 millimeter LEDs and toggle switches he needs to put in the surface mount resistors. Otherwise, it’d be really hard to get at them later. While mounting on tact switches, Ben reminds you to start with the low stuff and work your way up to the high stuff. If pads have uneven amounts of solder, that can cause tombstoning. After the LEDs and switches are in place, Ben gets to work on programming it. Ben is able to get everything working except for the piezo buzzer. The circuit that he wired up works with a transducer speaker so the audio is there but it’s very quiet. He then flips through the switches to go through hex free mode, hex game mode, decimal free mode, and decimal game mode.