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MintyBoost 3GS solution?
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MintyBoost 3GS solution?

by nerdydude101 on Fri Jun 28, 2013 8:26 pm

So i just build my mintyboost and it works but the problem is i have an iphone 3GS... Is there any real solution to the fact that it always says its not supported? Please help, its much apriciated? I also had the idea, if i buy the chip that is used to make it compatible and i buy the one currentally used in apple chargers (i found the one in a car charger) could i replace the chips to make it work???
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Re: MintyBoost 3GS solution?

by adafruit_support_bill on Sat Jun 29, 2013 5:50 am

The 3GS is one of the more fussy iPhones with respect to charging. Have you tried shorting the two data pins together? Make sure that you are using fresh high quality batteries. See our battery recommendations here: viewtopic.php?f=15&t=22377

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Re: MintyBoost 3GS solution?

by nerdydude101 on Sun Jun 30, 2013 11:01 am

How do i short the D- and D+ parts, and is there any chance for this damaging the mintyboost?
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Re: MintyBoost 3GS solution?

by adafruit_support_bill on Sun Jun 30, 2013 11:30 am

You can just add a blob of solder that bridges the two middle pins together. See the last step here: http://learn.adafruit.com/minty-boost/solder-it
This won't damage the Minty.

Image

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Re: MintyBoost 3GS solution?

by nerdydude101 on Sun Jun 30, 2013 9:01 pm

If i do this does it still work with say the IPhone 4, 4S, 5 and all other usb charged electronics? sorry for the questions but i want to make sure if i do something its not going to make it only work for 1 thing and not anything else
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Re: MintyBoost 3GS solution?

by adafruit_support_bill on Mon Jul 01, 2013 5:54 am

Almost all newer phones work fine with D1/D2 shorted. It is actually part of the new USB charging standard.

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Re: MintyBoost 3GS solution?

by nerdydude101 on Mon Jul 01, 2013 3:47 pm

thanks
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Re: MintyBoost 3GS solution?

by Dave X on Tue Sep 10, 2013 12:57 pm

"The 3GS is one of the more fussy iPhones with respect to charging." -- this might be a nice note for http://learn.adafruit.com/minty-boost/compat-v3 Maybe "Works 99% - See forum." would be good as well.

I'm having the same fussy 3GS problem. I've soldered the D+/D- together, I measure 4.98 V between USB +5V and GND, and 1.98 from GND to D+/D-. I've tried both new duracells, and charged 2500 NiMH, and repeatedly get the charging is not supported on this device alert.

I have not yet tried grounding the shield, and might try that tonight.

Were there hints about other possible solutions?
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Re: MintyBoost 3GS solution?

by adafruit_support_bill on Tue Sep 10, 2013 1:45 pm

I measure 4.98 V between USB +5V and GND

Does that hold pretty steady as you plug in the phone to charge?

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Re: MintyBoost 3GS solution?

by Dave X on Wed Sep 11, 2013 10:58 pm

My DMM isn't fast, so I don't notice a big transient, but I do see offsets.

The voltages I get are below for Energizer 2500mAH NiMH and Duracells,

Battery, VUSB, VData -- Config
3.068, 4.992, 1.990 -- Duracell, Disconnected
2.940, 4.979, 1.846 -- Duracell, Connected
2.584, 4.992, 1.990 -- NiMH, Disconnected
2.127, 4.983, 1.846 -- NiMH Connected

Is a shorted D+/D- of 1.846V too low under load? If so should I try lowering R2,R4 a bit? I saw a suggestion of 68K or lower on a different thread. I've got some 1/4 watt 5% 68K resistors around. I could try those if you think that would work.

If I'm doing the math right, it seems like the 3GS senses the shorted D+/D- with an equivalent pulldown resistor of about 190K. In parallel with R1/R2 this makes an 22.1K equivalent pulldown,... times 3/2 to get back up to 2V should need 2 66.3K (68K) resistors. Which should then give an open circuit VData of 2.1V.

Req = Rpu*(VData/VUSB)/(1-VData/VUSB)
Rsense=1/(1/Req-1/Rpulldown)

Shorting the two datalines makes Rpullup=37.5k, and Rpulldown=25k so to get these Data voltages while connected the equivalent pulldown (Req) and my iPhone's sense resistor seems to be:

Req, Rsense
22.1k, 190K -- Duracell Connected
22.1k, 190K -- NiMH Connected

So the sense current for my particular iPhone 3GS is 1.846/190K=10mA. I wonder whether the less finicky iPhones use a pair of bigger pulldown resistors?
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Re: MintyBoost 3GS solution?

by adafruit_support_bill on Thu Sep 12, 2013 6:14 am

Not much VUSB sag under load. But the VData change is not proportional. 1.846V is a bit on the low side.

The other variable here is the cable. Some cables have enough resistance to make a difference. Extra-long and/or 3-rd party cables are the worst offenders, but we've seen problems in some official Apple cables (or maybe they were just really good counterfeits).

I'd try a few different cables first to see if it makes a difference.

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Re: MintyBoost 3GS solution?

by Dave X on Thu Sep 12, 2013 9:59 am

Thanks,

I've just got the one cable that came with my used phone. I'm not sure if it's official Apple or not.

You should only expect a proportional VData reduction if the input impedance if the iPhine is infinite. If Apple attached a pulldown resistor to read the D+/D- lines and keep them from floating, you'd get just this sort of non-proportionality. Maybe the 3GS has smaller sense resistors than the rest of the iPhones and put a heavier load the data lines?

If the 1.846V is marginally low, maybe trying the 68K suggestion from viewtopic.php?f=15&t=16699&p=90611&hilit=3gs+68k+68k#p90611 would help. What is normal VData for a 3GS under load?

I'll look for a new cable, but trying the 68Ks might be easier.
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Re: MintyBoost 3GS solution?

by adafruit_support_bill on Thu Sep 12, 2013 10:16 am

Apple has no published spec on it. We only know what we can glean from reverse engineering & VData below 1.9v is iffy for most phones. The VData lines on my old clunker 3G (non S) only drop by 1 or 2 mV (compared to about 4-5 mV for VUSB). Clearly something different in the 3GS circuitry.

The 68K solution sounds like it is worth a try.

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Re: MintyBoost 3GS solution?

by Dave X on Mon Sep 16, 2013 12:07 am

I tried adding a 330K in parallel to the 75Ks 1/(1/330+1/75+1/75) to get the effect of replacing the 75ks with 68ks w/o desoldering. That got the Vdata up to to 2.120 unloaded, 1.998 loaded, but still no joy.

I also tried 3 NiMHs with the stock 75s, and that didn't seem to help.

Is the transient response important? Is there some sort of handshaking negotiation going on with iCharging? For DC response, it seems like cable quality could only be some function of resistance, and if I've got problems with my 3GS on the Mintyboost.

I'll try a connection cycle with an oscilloscope to look for transients.

I'll also try different cable, but in DC, what would a "quality" cable mean? Less resistance, which would cause less voltage drop between the mintyboost and the 3Gs?

I'd have been less surprised by these problems if the compatibilty doc said something a little less certain than "Works" for the 3Gs.
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Re: MintyBoost 3GS solution?

by adafruit_support_bill on Mon Sep 16, 2013 6:46 am

I don't believe there is any active handshaking, but I've never put a scope on it. Let us know what you find.

We don't hear of many problems with reasonably new genuine Apple cables. Older cables, 3rd party cables and extra-long cables are often a problem. I suspect it is simply a matter of resistance.

Thanks for letting us know what you have found. I have edited the compatibility doc to say "works with most". If you cannot get it to work with yours we will be happy to refund your purchase. Just contact support@adafruit.com with a link to this thread.

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Please be positive and constructive with your questions and comments.