MintyBoost

MintyBoost Tucked Into Its Minty Box

At left is a “Minty Boost v2.0” that Roger and I put together over the course of a couple of evenings.

The Minty Boost is a tiny power supply designed to provide power or to charge most USB devices.

Including the iPhone 3G, which really wants somewhere around 500ma to charge. Normally, to achieve that level of current, the devices have to negotiate with each other.

The MintyBoost is a “dumb” USB power source in that it mimics the wall wart (very very tiny wall wart) style USB power supplies, providing enough bias on the data lines to make the device pull current without going into “negotiation” mode.

MintyBoost Detail; No Crappy 7805 Here!

As a power supply, the Minty Boost is both smart and efficient. It is built around Linear Technology’s LT1302 Micropower High Output Current Step-Up Adjustable and Fixed 5V DC/DC Converter.

Combining the chip with a handful of discrete components creates a power supply that produces a steady 5 volts @ 600 milliamps. It is designed for use with 2x 1.5 volt cells and will continue to operate even until the combined voltage output by the in-series cells drops to 2 volts. When not in use, the chip draws extremely little current.

I’m using GreenBatteries.COM’s Ultra Low Self Discharge cells. These rechargeable batteries are specifically designed not to self-drain over time when not in use. Perfect for remote controls and camera flashes that don’t get used all the time (or are used rather intermittently when you think about it).

I’ll likely pick up a set of the high-capacity non-ULSD rechargeables.

The whole assembly is hot-glued into an Altoids tin (with a bit of electrical tape as insulation). Very convenient packaging and it is still quite easy to pop out the batteries.

It works quite well, though differently than other battery packs. Namely, the device actually charges the iPhone’s battery. That is, it isn’t an extender. As such, the iPhone will happily suck whatever current — 600ma, in this case — out of the device until either the iPhone’s battery is charged or the charger is drained.

The one caveat is that the device can actually drain the iPhone’s battery as the current falls. You need to keep an eye on things and pull the charger’s plug once the iPhone’s battery icon changes from “charging” to “powered”.

A small bit of inconvenience given that the device is around $20 and I don’t ever have to click “OK” on the “external device may be incompatible with your phone” dialog.

You can buy the kits from Lady Ada’s store. It is fairly straightforward to solder together, too.

Alternatively, you can try to grab the parts yourself. I had a hard time finding the LT1302 power supply chip at a reasonable price (including shipping). Turned out to be cheaper just to buy the kits.



8 Responses to “MintyBoost”

  1. benh57 says:

    Just don’t try to get one of these through airport security… i saw a horror story about just such a charger once. TSA not happy.

  2. Ben Holt says:

    I had no trouble at all flying with my homebuilt charger – basically just four AAs and this little circuit (had the same issue with it depleting my iPhone battery when the pack ran low, however)

  3. Alexander says:

    I had no issue with carrying mine through security last December. I’m really glad this was posted. I’ve been trying to diagnose the problem with my friend’s minty boost and now I finally have (depleting the battery on his iPod Touch)! Thanks!

  4. Costa says:

    H,

    Does anyone know if you can get the Minty Boost in the UK?

    I will check but I thought I would ask while I am here as my son has been driving me mad about his ipod needing charging all the time.

    If I cannot find a Minty Boost in the UK I will be back to find out how to make one.

    All The Best – And Happy New Year
    Costa

  5. bilbo says:

    I bought a couple of these kits direct from USA Ladyada, shipped to UK last year. I assembled the kits – excellent pieces of engineering. Extremely pleased. You will be liable for UK VAT and Post Office fleecing ( oops I mean ‘handling charges’). I will probably have more shipped to get the new LT1302 converter.

    good luck

    bilbo

  6. Digital Scale says:

    Hey, how long does it take to put one of these kits together? I’m pretty new at hacking but it looks like this one might be a bit much for me? That’s pretty sweet that your using an altoids can lol.

  7. Zaphodikus says:

    Still keen to find the chip in the UK, an alternative to max756 is the MC34063A -P1G for DIL, but no stock currently in the UK. I know you can get them in the UK, has anyone been able to, since the chip should cost less than a pound on it’s own locally, whereas postage plus the customs charges will be about £10.

  8. Zaphodikus says:

    Just back-ordered a few 3406’s – I see it’s the one used in a cheapo nokia car-charger, so if you have £10, you can pick one up and just desolder the part. Although for my purposes I’m going to assume the current limiting is set to 1amp, and shift my D+ line to 2.8v (3volts for simplicity) and the D- to 2v, using .125w resistors 22k and 22k, with a 10K in between. Dry run this afternoon will tell the truth I hope.

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