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While waiting for the parts to arrive, I pulled out my old soldering iron and other tools. It had been quite a while since I'd used them. Since I'm now living in a house with small children, I also put together a portable workbench, that closes up into a rather large wooden box. The lid opens down to be the bench surface, and the box holds all the tools and parts that I'm working on. I could have put it all in the garage, but I'd rather be able to spend the time with my family. Too bad I can't do the same for the drill press...
The parts arrived in a few deliveries, from Miles Tag, Mouser, and Digikey. I'd also picked up some nice new lead-free RoHS no-clean-flux solder at Fry's, along with a replacement soldering iron tip (my old one was rather pitted). I hadn't realized the flux was so, um, tame that I'd need to take extra care to keep the tip tinned. The habitual sponge-wipe before putting the iron back in the holder just wasn't enough. When the brand-new tip started turning black, and solder would bead up and roll off (when it actually melted; the oxide was a thermal insulator as well), I looked for a reason. I suspect using my old tin-lead rosin core would have been easier, but I wanted to keep the stuff in the house, and my 2-year-old is too likely to find and eat small things. With cleaning and re-tinning, the tip was back to normal, but it certainly seems to need more frequent cleaning.
With the parts in hand, I soldered the components to the 5.XX circuit board. The board itself is very nice, well laid out (only two pairs of holes close enough to require extra care), and well marked. I followed the assembly order suggested on the MilesTag website, only noticing later that the website's list doesn't mention two components (R13 and F1). My guess is that R13 should be added with the other discrete resistors, and F1 after the electrolytic capacitors but before the Molex connectors.
|The 5.XX board, with resistors added.||5.XX, about halfway assembled.||5.XX, ready for voltage test.||Mounted on a plastic plate.|
After assembling the board (except for the PIC), I measured the voltages at the various test points described in the Miles Tag technical manual. Everything came out as it should have, which was a relief, as my prior electronics projects were far in the past and had rather larger components.
There were a few forgetful moments, and a few glitches when it came time to install the PIC and test the board for function. I'd exchanged the IR LED leads, and that caused the board to complain of a dead IR LED. I'd also used a multi-turn trim pot for the LCD contrast, and it took a while to realize I had to turn the screw around and around and around before seeing any result. I'd forgotten the two soldered wires (LCD backlight -BL, ISD +B), and had to dismount and remount the board to take care of that. Memo to self: check and double check the wiring lists. Second memo to self: design the next one to be easier to work on.
I had wanted to build the sound board about the same time as the main board, but Miles Tag was sold out of their ISD-PCB, so I would have had to order using the open designs at rather high cost, or etch them myself (an activity I didn't want to experiment with at this time). I mentioned this on the Laser Forums, and Jim Robertson kindly offered me some Rev B boards at a nice price.
I assembled the sound board in order of component height, since that makes it easier to keep the things tight to their holes, especially the ones whose leads don't bend easily. That turned out to be this order:
Since I had a Rev B board, there were 2 errors I needed to be aware of. They're both documented clearly on the Miles Tag ISD page, so it wasn't a surprise. Reversing the polarity of C2 was simple, just put the thing in backwards. The jumper wire from C1 ground to J1 G was also simple, since I cunningly bent the negative terminal of C1 down flat before soldering to form the jumper. No worries about finding a spare piece of bare wire. Rev C boards don't have the errors, so there's no need to worry about this if you've got the up-to-date boards.
I put automotive insulated disconnects, which I had lying around, near both ends of the battery wire, so that I could remove the board from the casing. Without it, both the main board and the sound board would have been tied to the casing, as that wire passes through a 3/8 inch hole in the wrist of the stock. I'm sure there's a better wire connector available, but those were handy and worked well enough.
When adding the board to the casing, I mistakenly wired the Molex connector mirrored (GND and FF swapped, +5V and CE swapped, PD and EOM swapped). Unsurprisingly, this didn't work, and seems to have damaged something. (Advice to self: don't work after you're tired, and don't hurry, even if you're close to finishing.) After I realized this, I corrected the problem and installed the other board, which I had wanted to use on my second tagger. A little adjustment to the trim potentiometer (R4), and the tagger had nice, loud, realistic sounds.
March 2007: Jim Robertson (Miles Tag) has announced that he'll be selling a combination through-hole board, containing the main board and sound board circuits on a single (larger) board. This will complement his pre-built surface mount board, also containing both circuits. It sounds like that should make some things easier, and I expect that I'd like to use that board in any future designs. Also, with the cancelling of the ISD2560 chip, this is likely one of the last boards to be built to this design.
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Copyright © 2007, Leif Bennett. All rights reserved.