MintyBoost 3.0


I built a pocket size USB charger using a MintyBoost 3.0 USB charger, a 3.7 v, 2600 mAh LiIon battery and a built-in LiIon battery charger in an Altoids Wintergreen Mints tin. It can be used to recharge a cell phone, iPod or other small USB rechargeable device.

I’ve had‘s MintyBoost 3.0 kit and USB LiIon/LiPoly charger (this is v1.1) for a while but I never put them together. I liked the size of the Altoids gum tin of the previous MintyBoost versions I have built but I wanted a little more charging capacity than 2 AA batteries could provide. I wanted a suitable battery and enclosure that didn’t compromise charging capacity and size.

Using ladyada’s calculations for battery power, I decided to use a 3.7v 2600 mAh LiIon battery.

The battery’s capacity:
MintyBoost mWh = 3.7V * 2600 mAh = 9620 mWh input

The amount of current it can provide:
Output mAh @ 5V = 9620 mWh / 5 * 80% = 1539 mAh output (80% is the conversion efficiency)

Number of iPhone 4S recharges = 1539 mAh / 1430 mAh (iPhone battery capacity) ~ 1.1

The MintyBoost kit requires the soldering of a few components to a circuit board. I also made two mods to the internal battery charger. With this version (1.1) of the adafruit LiIon battery charger, removing the resistor R4 and replacing it with a 1K ohm resistor allows the internal battery to be charged at 1000 mA.

The internal battery charger has connections for external status LEDs. I connected current limiting resistors between the board and LEDs, then mounted the LEDs in holes in the Altoids tin. The green LED indicates that the internal battery is charging and the yellow LED indicates a fully charged battery. (LiIon/LiPoly charging tutorial at Adafruit Learning System)

The battery and circuit boards are mounted in the Altoids tin with double sided foam tape. I made a miscalculation in the height of the LiIon charger taped to battery – the cover won’t close when the charging cable for the internal battery is attached.

To charge the internal battery, a USB Mini B plug supplies the power to the internal battery charger as in the photo above. To charge a device, a USB Standard A connector is used. There’s also enough room in the Altoids tin for storing an Apple 30-pin to USB Cable.

MintyBoost 3.0 in Altoids Wintergreen Mints tin

Below are charging test results with an iPhone 4S starting with battery at 49%:

Time (minutes)      Charge (%)
0:00                           49%
0:15                           58%
0:30                           66%
0:45                           75%
1:00                           83%
1:15                           89%
1:30                           93%
1:45                           96%
2:00                           97%

If you are interested in the MintyBoost design process:

MintyBoost USB Charger v1.1

Update: This post is about version 1.1 of the MintyBoost. ladyada has updated the kit to version 3.0.

In high school, I used to love building electronic things. That was so long ago, I was using vacuum tubes to make power supplies.

Once I made an audible tachometer for my car from a schematic in Popular Science. I even thought I wanted to be an EE and started at UC Berkeley in the School of Engineering. After a few quarters I realized that if I didn’t like learning engineering, I probably wouldn’t like doing Minty Boost Componentsengineering. (I think my friend Dan Kalman told me that)
Over the years, I still enjoyed making electronic things. Back in the mid 70’s, I had just moved to New York.

As a photo assistant, I used an answering service home answering machines weren’t in wide use.
By the late 70’s, I bought an answering machine and a pager. In those days, the only people who used pagers were doctors. I needed a way to know immediately that I had received a message on my answering machine.

I put a roller switch on one of the answering machine cassette solenoids that triggered a bunch of 555 timers. That dialed my pager’s number from a chopped up Radio Shack phone that had my pager’s numberprogrammed in one of the speed dial locations.

Minty Boost Circuit Board

Years later, answering machines had their own call transfer feature.
When Make Magazine started publishing, I became a charter subscriber. The projects they were doing were all the kinds of things that I used to do. One of the projects I saw at the Make Blog, was kit called the MintyBoost, a USB charger designed by ladyada, that fits in an Altoids tin and runs on two AA batteries.

MintyBoost Solder Side

It basically takes the 3 volts from the batteries and boosts it to the 5 volts that USB devices use. Since we have a couple of iPods and cell phone that can be charged with the MintyBoost, I bought a kit.
You can update the v1.1 by adding a resistor.

It’s a great beginner’s kit and easy to assemble. You have to solder the components to the circuit board but you’ll learn basic soldering skills in the process.

MintyBoost Case

The hardest part for me was finding the Altoids gum.

Once you’ve built the charger, you’ll have a something that is useful and may give you the satisfaction of making something yourself. That’s got to be worth something.