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[Group Buy-5][D]MTK3339 GPS + BoosterPack - $14.26

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I just came across these little beauties:

http://www.goldmine-elec-products.com/p ... er=G13133A

 

Provided the figures are correct on both datasheets, one of these would last about a day as a backup for this GPS module. And the 15c price tag means more than one can be used.

 

I got a few of these the other day and they are basically useless. They discharge from 3V to 2V in a matter of minutes when not connected to anything. Do not buy them for memory backup.

 

How did you test that? I got a few too, and took those tabs of and slotted it into the launchpads power connector thing (J6) and it lasted a good few minutes running one of the LEDs. I think I did leave it to charge for a while though, they do call em batteries, so I guess they have charge characteristics some where between a battery and a capacitor.

 

TL;DR try charging them for longer.

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I just came across these little beauties:

http://www.goldmine-elec-products.com/p ... er=G13133A

 

Provided the figures are correct on both datasheets, one of these would last about a day as a backup for this GPS module. And the 15c price tag means more than one can be used.

 

I got a few of these the other day and they are basically useless. They discharge from 3V to 2V in a matter of minutes when not connected to anything. Do not buy them for memory backup.

 

How did you test that? I got a few too, and took those tabs of and slotted it into the launchpads power connector thing (J6) and it lasted a good few minutes running one of the LEDs. I think I did leave it to charge for a while though, they do call em batteries, so I guess they have charge characteristics some where between a battery and a capacitor.

 

TL;DR try charging them for longer.

 

I have no doubts that these batteries can run an LED for a few minutes. What I was trying to convey in my previous post is that there is very significant leakage current that causes the batteries to discharge very rapidly with no load. They are not a good choice for preserving almanac data in MTK3339.

 

I used a regular multimeter to test the voltage. I did try charging the batteries longer, with no noticeable difference.

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I used a regular multimeter to test the voltage. I did try charging the batteries longer, with no noticeable difference.

 

I've seen multimeter resistances as low as 1Meg, that could be drawing a decent chunk of current(3uA), when comparing to the standby current draw of the MTK ~7uA.

 

They are not a good choice for preserving almanac data in MTK3339.

 

I do agree with you on this one. A CR2032 would last 10 years as battery backup for the MTK provided there would be no self discharge.

 

These little caps are very cool though.

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There is a newer version of MTK3339 available from the same seller on AliExpress:

 

http://www.aliexpress.com/item/FGPMMOPA6H-utilizes-the-MediaTek-new-generation-GPS-Chipset-MT3339/623742154.html

 

The main differences are size (new unit is 20% thinner: 4.7mm vs 6.2mm), pinout, and presence of an input for an external antenna. The module automatically switches between the built-in and external antennas. As far as I can tell, everything else is the same.

 

This is what Adafruit now sells as their "Ultimate GPS module":

 

http://www.adafruit.com/products/790

 

Datasheet:

 

http://www.adafruit.com/datasheets/GlobalTop-FGPMMOPA6H-Datasheet-V0A.pdf

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