Surface mount technology is within reach of everyone. There's no special technology being used here. The iron is a normal 25W soldering iron, it's just normal electronics solder, and the soldering in the photos is being done by my 11-yo son, who has barely soldered before. Thanks Tim!
The first thing to start with is the ATtiny85 microcontroller. When I was a lad, we were told to add the semiconductors to our project last, because of the danger of damage from static. The reason I'm putting the microcontroller on first is because we need to program the chip, and the other components can interfere with programming.
Here's a pic of the chip perched on the board. I've lined up the pins with the PCB pads. Since we will first solder just one pad, it's not critical that all pads are lined up, just the corner pad that gets soldered first:
|Chip perched on board|
|Pressure applied with mini garden fork|
|Soldering the first pin|
After the first pin is soldered, you can gently rotate the chip to get all the pins aligned.
|One pin soldered, the chip can be aligned|
|Soldering the rest of the pins|
|Fixing solder bridges with soldering braid|
|AVRStick and programmer|
To line up the pins with the pads on the circuit board, I made a sleeve out of three pieces of cardboard, glued together as a sandwich. Holes drilled in the top piece of cardboard line up with the pads on the PCB. I slide the PCB into the sleeve, then using one hand, I can hold the bed of nails and the sleeve together. With the other hand, I can press Enter on my computer to run the command to copy the firmware to the micro, and set the right fuses (for example, the fuse which turns on the clock PLL that I mentioned earlier).
|Playpause with bed of nails. The PCB in this pic doesn't have a chip, but of course for programming it would need to have one.|
The PCB traces at one end of the board are just the right shape to work as a USB connector. But the copper isn't very thin, and if used often, the other part of the connector (the part in your PC) will wear away the copper. To avoid this, you can tin the USB tracks with solder:
|Tinning USB connector traces|
You can use the gardening fork on all the components except for the diodes, if the diodes are cylindrical. For the diodes, you can ask a friend to hold the diode in position with a small screwdriver.
And now a small admission: When I was copying and pasting the layout to make ten boards, I accidentally deleted a track. That track was omitted on all ten boards I made. So here a small wire is being soldered on to act as the missing track. All the other components have already been soldered.
|All passives soldered, doing the switch (extra wire)|
Note that having additional components can interfere with the programmer, but in this case, it seems to work:
|Playpause hot-wired to programmer|
|Five completed playpauses|
So, I now have a Playpause to use at work when I'm listening to music, and I can now apply my knowledge of making PCBs and doing bed-of-nails programming to the USB Doodad. Maybe you can too. If you have any questions, or want help making a Playpause or PCBs, ask me.