Monday, December 10, 2012

TV-B-Gone Redesign Part III: Assembly

     After receiving the sheets, the next logical step is to put everything together.  Between the time I ordered the PCBs and when they came, I ordered the parts to solder on.  Here's a side-by-side of the parts I used, and the parts LadyAda used, hers are on the left, mine on the right.
Micro:   ATTINY85V-10-PU     ATTINY85V-10SU
Oscillator:   CSTLS8M00G53Z-B0     CCR8.0MXC8T
Cap_1:   UBR0J221MDD     2x: LMK316BJ106KL-T
Cap_2:    C315C104M5U5TA     N/A
EU Resistor: 1/4W, 5%, 10K     N/A
Status LED Resistor: 1/4W, 5%, 1K     MCR10ERTF1000
Output LED Resistor: 1/4W, 5%, 1K     2x: ESR10EZPJ8R2
Narrow LED:   2x: EL-IR333-A     SFH 4545
Wide LED:   2x: 638-IR333C/H0/L10     OED-EL-1L2
Tact Switch:   FSM4JH     PTS645SK43SMTRLFS
Leading Transistor:   PN2907ABU     FDN335N
LED Transistor:   PN2222BU     N/A
JTAG Header:   961206-6404-AR     N/A
Battery Holder:   2463K-ND     22-0421-R-GR
     All of my parts can be found on Digi-Key, except for the battery pack, which can be found on Mouser.
     The sheets had 50 units per sheet, so I had to separate them somehow.  Now you may ask yourself 'Why didn't you order the boards with holes punched in them, so you could break them apart by hand?'  The reason is, that sequentially punched holes like that are against the agreement when ordering boards, and you'll either have to pay a huge price for it, or you won't get the boards.  So I had to use a bandsaw.
     Lucky for me, my old man used to do woodwork, so our entire basement is basically a woodshop.  Also lucky for me, he had a bandsaw blade with teeth fine enough that roughly two and a half teeth fit into the board at any time, which he said was required for safety reasons.  After a simple blade swap, I began cutting the boards.  Unfortunately, I suck at cutting straight (the boards went under the guide), so I ended up with some pretty ugly units.  However, after a couple hours of sanding, all 50 boards looked decent.
     Now I'm stuck with a bunch of incredibly tiny parts, and 50 boards.  Another wave of help from the old man comes when he brings home some magnification glasses, a board holder, and tweezers.  The largest part is less than a quarter inch in length, so maneuvering the parts into place is hilariously difficult.  Each part is so small that the mere static from your finger will keep it from landing on the board.  Tweezers were a godsend.  The magnification glasses were very helpful in the beginning, but as I got into the rhythm of things, I found myself using them less.  The board holder is something I also love.  It allowed me to (at my peak) work on six boards at once, a far cry from the one I would be working on otherwise.
     Soldering methods range wildly depending on experience, part type, and personal preference.  I found it easiest to solder one pad, then remelt the pad while placing the part into it with the tweezers.  Then I could go around and solder the other pads down, making it especially easy to solder the microcontroller down.
     I generally did the micros first, then did a couple parts at a time, and the LEDs were second to last followed by the battery pack.  Sit back, pop on some music on Pandora, and solder away for a few hours.
     The buttons had to go on last.  I thought I was clever when designing the boards, placing the JTAG programming header under the button.  I thought I could program it from the reverse side of the board.  Unfortunately, without rewiring the header (alright, that's a 5 minute solution, but still) that's not possible.  Not a big deal.  Just solder all the parts, program, then solder the button on.
     To package it up, I had to clip the wires from the battery pack to be a half-inch and solder them to the boards.  The boards were mounted with double-sided tape onto the battery housing, so that the LEDs sat on the edge of the housing, avoiding any bending that may occur. Pop in the batteries, and it's done!

1 comment:

  1. Be careful with those SFH4545! They can emit enough light to cause eye damage when driven with high current pulses, something like 7 Watts per steradian. That is fine for someone like you or me who knows better than to put them right in someone's eye, but if you are going to be handing these out to high school students, there is a potential for bad things to happen. The only thing I can liken this to is a LASER. There is just so much light focused into such a small area. Please keep those series resistors above 5Ω on any boards you give/sell to your classmates.