MintyBoost XL - Custom MintyBoost

by RobertHunt, published

MintyBoost XL - Custom MintyBoost by RobertHunt Apr 7, 2010


This is my modification of Ladyada's excellent open source MintyBoost kit that is documented at ladyada.net/make/mintyboost.

My modification consists of a custom PCB design based on the original schematic that it slightly larger than the MintyBoost's PCB but is single sided with no links and has room for two battery connections. It is still small enough to fit in a large Altoids tin along with 4x AA batteries.

You have the option of running the MintyBoost XL at 2.4v - 3.0v by putting the two pairs of 2x AA batteries in parallel or running it at 4.8v - 6.0v by putting the two pairs of 2x AA in series. The LT1302 runs at a maximum input voltage of 8.0v so the higher voltage produced by the batteries in series isn't an issue. Running in parallel might cause issues if the battery packs are not evenly charged as it may result in the higher charged one draining into the lower one. You have the option to decide when building as there is room to connect them in parallel on the PCB.

The resistors that I chose for the D+ and D- pins of the USB connector were 100k as I wanted it to work with my iPhone 3G. Some devices are fussier than others, most notably Apple's newer products, you may need to adjust the design to get it to work. See Ladyada's documentation and forums for more information about this.

To etch the PCB I used the toner transfer method which is extensively described at fullnet.com/~tomg/gooteepc.htm. Basically it involves printing the track design onto photo paper with a laser printer and then ironing it onto the copper clad board. After it has transferred to the board it is soaked in water to remove the paper which leaves an etch resistant layer of toner on the copper board. It is then etched in a corrosive solution such as ferric chloride to remove the remaining copper. Be sure to wear safety glasses, protective gloves and suitable clothing when dealing with etching solutions and keep it away from anything metallic.

The toner transfer method isn't perfect as the quality can vary quite a lot and requires a bit of tweaking. The real beauty of this method is that you can always scrub off the toner before you etch if you're not happy with the quality and try again.

Altoid tins are notoriously hard to get hold of in the UK but luckily Marks & Spencer sell "Curiously Strong Mints" which are identical to Altoid mints and come in the same sized tin.


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1. Etch the board design onto copper clad board using your desired method.
2. Drill the holes in the etched board.
3. solder al of the components in place.
4. Cut a hole in the tin for the USB connector (Dremel or snippers are handy).
5. Insulate the metal by the circuit board and glue the board into place.
6. Insert 4x AA batteries.
7. Charge you gadgets on the go!

You will more than likely be stopped by airport security if you take try and take a device like this on board despite it being harmless.
This design corresponds to 2.0 version of MintyBoost, right?

Did you update schematics for 3.0 version?
Great info! Do you have an Eagle formatted file of the circuit? I want to make my own as well...

The .brd and .sch files are Eagle formatted files.
What resistor values should I use for iPhone 4?
2x 100K resistors work on my iPhone 4 but it's best to give it a test on breadboard before soldering it up as it may be different. I have one of the release iPhone 4's, it could well be different for iPhone 4's made today or the CDMA version so it's best to test it first.
Thanks, what values should I be looking for on the output?
going do make one with printed casing and and Bike mount clunch
I've started my own take on this project. I've taken your schematic and given it a little more "flair," and mastered the art of laser toner to PCB transfer. The result is pretty awesome. It's too bad I only have single sided boards - double-sided next time! :)

Now I'm just waiting on my FeCl powder. It should be here any day...
Here's a good guide for the toner transfer: riccibitti.com/pcb/pcb.htm

I used the stupid ads in the back of the Economist for my paper and it was AWESOME. I knew those old magazines would eventually be good for some
thing! Thanks for the awesome design and instructions. Also, I picked up the following IC - do you think it will be an adequate replacement for the LT1302? Digikey and Mouser are all out of the 1302 and most of the other possibilities from the original Mintyboost.

Erik - in reply to Erik
Well, I finished drilling and soldering the board together today. It worked! The only problem is the LT1303 apparently only puts out a maximum of 200mA. My Android phone gets all angry when I try to charge it (but it does detect the 5V and start trying to charge). I'll be upgrading to an LT1302 or similar if I can find one on the market for a decent price! Thanks a bunch! :-D
is there anything i can use instead of lt1302, its not avaialable in india,, cant i use a max 756
what is the size of the pcb
It's about 40mm x 25mm. There is plenty of space to fit it in an altoids sized tine with 4x AA batteries.
Robert, the inductor and resistor values on part list and schematic are not identical. It seems the 1uH makes no sense, what I have found out on the data specs. But what about the resistor. Could you please fix this issue. Anyway, the whole project seems pretty awesome. I will probably do it without making a PCB. To much hassle for this kind of circuit. :-D
The inductor should be 22 uH but it's not critical, pretty much any old inductor will do. As I mentioned in the description, the resistor values are variable depending on your application, they can be completely omitted in many cases. It depends on how fussy the device you are trying to charge is.

If you need any more information it's worth visting ladyada.net/make/mintyboost as my design is almost identical to the regular MintyBoost.
Dump the ferric chloride, muratic acid and hydrogen peroxide much cleaner and easier to work with. Look it up on the internet.