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Step 4The Process: Enclosure selection
So at this point I start thinking about enclosure and size. Most people think of this last, and that's a bad idea. If there's one thing I've learned from hacking on electronics, its that you should try and select the case first because it dictates a lot of the electronics and interface.
I know that the parts for the kit must be all through-hole (no surface mount) and easy to work with. I also want AA batteries, 2 is good although I know from experience that most boost converters will work with any number from 1 and 3 just fine. I have a predilection for Altoids tins and I also know that I can fit ~2 AA's into a gum tin so I pull out a tin and take some measurements.
OK 2 AA's fit well, so now I rummage through my collection of battery holders and find one (PCB-mount) which seems to be pretty good, it doesn't have a switch but I don't need one anyway (see quiescient calculations, later on)
So I take some measurements...Looks like I have about 1.25" x 0.7" semicircular PCB space at the top for the circuit board.
I also try out another battery holder I have, this gives me more space, 1.25"x0.85"...but the batteries go in sideways so one would have to remove the holder to change the batteries. I'd prefer that you can just take them out directly, so I don't go with this one (it also turns out I don't need that extra space)
(I now do a little hack to turn the PCB mount 2xAA battery holder into a wire-lead one. Basically I just solder on red and black 6" wires and clip off the PCB through-hole leads. This is actually a little difficult because the plastic melts and you have to sort of keep it in place while you solder. Its not suggested :) )
Now that's done I'm ready to think about what I can cram into that space.
I know that the parts for the kit must be all through-hole (no surface mount) and easy to work with. I also want AA batteries, 2 is good although I know from experience that most boost converters will work with any number from 1 and 3 just fine. I have a predilection for Altoids tins and I also know that I can fit ~2 AA's into a gum tin so I pull out a tin and take some measurements.
OK 2 AA's fit well, so now I rummage through my collection of battery holders and find one (PCB-mount) which seems to be pretty good, it doesn't have a switch but I don't need one anyway (see quiescient calculations, later on)
So I take some measurements...Looks like I have about 1.25" x 0.7" semicircular PCB space at the top for the circuit board.
I also try out another battery holder I have, this gives me more space, 1.25"x0.85"...but the batteries go in sideways so one would have to remove the holder to change the batteries. I'd prefer that you can just take them out directly, so I don't go with this one (it also turns out I don't need that extra space)
(I now do a little hack to turn the PCB mount 2xAA battery holder into a wire-lead one. Basically I just solder on red and black 6" wires and clip off the PCB through-hole leads. This is actually a little difficult because the plastic melts and you have to sort of keep it in place while you solder. Its not suggested :) )
Now that's done I'm ready to think about what I can cram into that space.
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This is enough volts that you don't need the IC that increases the voltage of two batteries. So all you need is the 7805 regulator and supporting parts.
And because of the large number of batteries, it would allow the ipod to work much, much longer. Probably three times longer as the two battery version. It might be worth it if you are camping, or off somewhere where you wont have access to AC power.
Downside is, you have a battery pack that is three times the size.
To put it another way, 4 NiMH cells in series doth a USB charger make. That's it.
If you want smaller size but no introduced energy losses due to the electronics connect 4 N cells in series. That will make a package about the size of 2 AA cells.