One of the skills I'm working on in December is soldering. After a failed attempt at making a Minty boost, I opted for the far more beginner style project in the Times Square watch.
The watch come as a kit from Adafruit. The kit includes:
- TIMESQUARE PCB - half thickness black PCB
- ATMEGA328P - preprogrammed microcontroller
- DS1337 - 8 pin real time clock chip
- 32.768KHz Crystal - thin silver cylinder
- Right angle buttons - two for either side
- 20mm coin battery holder
- 0.1uF ceramic capacitor - yellow blobby
- 1 x 10K resistor - brown black orange gold
- 8 x 47 ohm resistor - yellow violet black gold
- 1.5" 8x8 matrix
The components are solder through on the PCB. As usual the tutorials Adafruit provide on-line are a perfect step by step instruction for assembly. I inventoried the pieces got set-up with a third hand, and went to work. With the magnifying visor I recently acquired, what once was a dreaded job, actually became kinda fun. I could see what I was doing, I could sandwich the lead and the iron, and the gently melt a perfect hershey kiss of solder into the hole.
It almost seemed too easy.
The last step of assembling the watch is attaching the 8x8 led matrix. Aka the lights you see on the front. It comes as a square cube like object with 16 pins on the back that get soldered to the PCB... almost too easy. I had been following instructions, soldering in each component in turn just as I was told. To that point the components had all been arranged on one side of the PCB and soldered in on the other. When I got to this last step I sort of, well, didn't finish reading the instructions. It was obvious which way it went on. So I put it on and soldered in all 16 pins, quite tidily too I might add.
Then I started looking at my finished product. I realized, unlike the rest of the components, this one was supposed to have had its pins pressed through from the opposite side, and THEN get soldered to the board. All 16 solder points I had just made, while pretty, were wrong. I did not panick, I did not curse, I didn't really even stop.
I decided if this was going to teach me to solder than it may as well teach me to desolder too. At this point I had no expectation of saving this project and I was simply learning a skill. My "goal" was to remove the solder from the 16 points, flip the led matrix to the right side of the board, and solder it back in correctly.
Most of desoldering is using copper mesh (think paper towel) to drink up the lower melting point solder (think spilled glass of water) that's on the PCB (think time counter top with holes drilled into it for water to seep into). After poking at it for more than an hour, I was able to melt, sop-up, and free all 16 pins, still in tact!
I flipped it over, got the pins reinserted correctly, re-soldered it, put the battery in, and wham, hello world.
Two things I think made the desoldering job tolerable:
1) Magnification: the geeky head-set is not just for show. It's like being able to visit that tiny little city on the PCB. Do yourself a favor don't be afraid to magnify.
2) Enough heat: I had the iron set just a little over 410C for the non-lead solder I was using. Having that much heat and fine control was invaluable. Do not scrimp on a cheaper soldering iron. It pays for itself in frustration.
The most important thing I learned? There's no shame in desoldering. In fact it's a skill all unto itself. Plus, it can be done successfully.
One last thing, with all this new found proficiency; after working on it for another 30 or 40 minutes yesterday, I still haven't got that pesky piece of solder out of the minty PCB. I think I may give that first attempt up as a lost cause.