Step 7: The Process: Rapid Prototyping

In reality, what I did was look through the Digikey catalog, where I only found the DN7418 inductor (the other one was somewhat hidden in the RF inductor section). And it showed up before the Mouser box, so I spent an hour or two making up a prototype.

The circuit itself is simple, I want one large electrolytic cap for low frequency smoothing on the battery, and an output cap pair (electrolytic and one ceramic cap for high freq. smoothing). I also need the chip, a reference voltage capacitor, the inductor and a schottky diode to finish off the boost regulator. I happen to have some 1N5818's, which are often used as schottky diodes in boost regulators. I also need a USB type A female jack, of course, and two holes to solder the battery pack into. You can compare the schematic to the topology diagram in step #3 keeping in mind that this chip has an internal transistor switch.

All these parts must fit into the space left over from the battery pack. I make EagleCAD library parts for the inductor and chip (the rest are already there) and lay out the board. I'm not going to detail making library parts in eagle or pcb layout, others have done so already. Use whichever software you want, I like Eagle because there's a free version available for download if you're just making small PCBs.

Since I am know this is just a prototype version, I make the PCB single sided -- for easy etching. I also make the traces really large. I print out a paper version of the PCB and punch the parts through to verify that they're the right shape/package.

I get my etching setup together, turn on the heater for the etching tank, and print out a bunch of tiled PCB layouts on toner transfer. I transfer the toner onto a single sided PCB and etch it in the tank

Then I clean off the toner transfer, drill the holes with a dremel drill-press with carbide drill bits, and cut out the shape.

Then I solder the parts in, and fit it into the case with the battery pack, using double-sided foam sticky tape to hold down both the battery holder and the PCB without shorting the PCB to the metal tin.

OK, done!
thanatos3703 years ago
If I wanted 2 parallel banks of 2 AA's to increase charger time, would your circuit work still?
TIDGE274 years ago
Great instructable!
Please may you send me the eage files
toby244 years ago
can you put all the components that needed in that project or all parts of the project..
so i can buy on the store..
caseykoh5 years ago
may i know more about the DC/DC switching controller  (with internal transistor switch) and the the schottky diode would look like? send me the pics,please and thank you ^^
mixadj6 years ago
well.... I feel stupid.
mixadj6 years ago
Could you please post a copy of the eagle file.
gosub6 years ago
Very nice work. Maybe I would make the USB plug fit within the box... Well done anyway . For DEVA : IMO any 16/25 Volts will do.
deva8 years ago
maybe a stupid question, but what 'voltage'-indication should the 100 ùF elco's have ?
y2kkmac8 years ago
I like your bike chain bracelet. :)
Kikulof9 years ago
I think ... thats good