PCB Stage
I have replaced the DIL version of the microcontroller with the SOIC version. After testing it on the prototype board, I am satisfied that it works. However, I am a little concerned about the speed of the roving eye since I do not have any copies of the nuBSG episodes featuring the Cylon Raider. Luckily, a search on Youtube produced some videos of the actual prop during the BSG Auction. So, the timing is a little closer to the original but not exactly the same speed. On the photo above, I am testing the circuit using 3x AAA batteries, which gives me 4.5volts but with the diode in place, I should be getting about 3.8volts instead. And if I use 2x AAA batteries, it is still OK because of the chips's 'LF' spec which gives an operating range from 2.0volts to 5.5volts. Note the small button battery on the top right of the picture. It is a a LR44 battery which gives 1.55volts. Initially I was thinking of using the batteries in the model and have them accessible via a hatch or the top part of the model, secured via neodynum magnets but then again, not many people would like to touch their models after it is done in case there are fingerprints or smudged paints.
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So, with the boards now filed to the desired size, the final curved shape will have to be grinded off with a rotary tool. This was the only way since the prototype PCB are made from FR2 or SRBP (Synthetic Resin Bonded paper) which cracks very easily and are not very friendly to repeated soldering. If you solder or desolder too much, the copper tracks will lift off from the board. |
After the grinding process, I test fitted the PCB onto the model kit and well, this is very good news indeed. Do not be concerned about the greenish tinge as this is the etch resist coating which I will sand it off later. In the real production board, the material used will be FR4 and it will be green, tough and well, easier to solder.
Populating the Board
I am very excited at this stage because it will now determine if my design works or not. And not only that, I have the opportunity to solder a SOIC chip plus a SMD Network resistor for the first time! I have come across SMD before, by other members from other Forums but try as I might, there was no opportunity for me to fully implement them until now. This is also the time where I can see for myself if the board needs further improvement or design changes since the image on the monitor can only tell you so much.
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The first component to be soldered is the Network resistor. Because of its fine solder pads, I have to test each resistor with a multimeter to see if they are really soldered on to the board or not. each step of the way, I had to use the meter. So far so good. |
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I am also starting to appreciate the importance of a good pair of tweezers when it comes to SMD soldering. Make sure the ones you get are not magnetized as SMD components are not only small but easily 'sticks' to any metal object. |
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I am very pleased with the Network's resistor's robustness. The key is to lightly coat the copper area/tracks with some solder prior to soldering. Then wipe it off with the solder wick. It does look messy now but once it is the proper PCB (I hope) the solder masks will make sure the solder stays in one place. |
Soldering Method
In order to sodler the SMD SOIC chip effectively, I have to use the solder wick. Usually, the solder wick is for desoldering jobs but here, I am using it for a two functions. The first is to use it to tin the copper tracks in the PCB. An dthe second, it for soldering the SOIC chip onto the PCB.
The first step you must do is to tin the copper tracks/pads. Then, carefully position the chip (and note its pin orientation) onto the pads. Solder one of the pins as this will hold the chip in place. The solder the other pin, on the other end at the opposite side of the chip. Now the chip is secure. Melt the sodler liberally on all the pins on one side of the chip. Once it cools down, repeat the same for the other side. make sure all of the pins have solder on them, never mind if they are all clumped together. At this point, as long as you do not power the board, it is alright. Note: To reduce the risk of burning the chip, I should have soldered the Network resistors first, followed by the 10 LEDs. And then only do I solder the SOIC chip. The was because after soldering the chip, I did the LEDs next. For every LED soldered, I tested it with the meter and the voltage from the meter went back to the chip which effectively, rendered it semi-useful.
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This is the part where the solder wick comes in. Gently place the solder wick onto the glob os solder and use the soldering iron on top of it. When the solder beneath melts, it will be sucked into the wick via capilary action, into the oxygen free copper. Oh, and when you do this, please hold onto the plastic casing of the wick and not the copper braid itself as it gets hot very fast. Make sure you check to mack sure each pin is soldered and not shorting with every attempt of the solder wick. |
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Repeat the same with the other side of the IC. And once everything has been checked for dry joints and shorts, you are now ready to witness the next step. |
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