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Gemini-1 mods.html
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<title>Gemini-1 PCB mods to extend battery life</title>
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<td class="h3">Recommend Gemini-1 PCB mods to extend battery life<br />
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<td class="style6">Please note that later versions of the Gemini-1 have this modification included.<br />
You can tell if it is as there is a 39kOhm surface mount resistor just
to the left of the RTC IC, which is connected between pins 2 and 9 of the IC as described below.
Obviously you should only perform the modification below if this
resistor is <b><i>not present</i></b>.<br />
<br />This mod is from the Gemini_Users group<br />
<a href="http://groups.yahoo.com/neo/groups/Gemini_Users/message/3584">
http://groups.yahoo.com/neo/groups/Gemini_Users/message/3584</a><br /><span style="color: #0000ee;"></span><br />Gemini's SRAM is not only used to store user catalogues and the
observation<br />
logs, but also an amount of parameters and matrices used for the
modelling<br />
algorithm. So it has a size of 128 kByte and is accessed (also for
writing)<br />
very often, far exceeding size and reprogramming life time of an EEPROM.<br />
<br />
Normally, the Li CR2032 battery should last at least one year and should<br />
keep the SRAM content safe and the RTC running. If CMOS Resets occur
after<br />
some minutes even with a fresh battery or battery lifetime is
significantly<br />
shorter than one year, I recommend the following patch for the
electronically<br />
inclined:<br />
<br />
1) Buy a small 39k resistor (with wires, not SMD)<br />
2) Solder it between pin 2 (the second from above at the left side)<br />
and pin 9 (the downmost at the left side) of the EPSON real time clock<br />
chip labeled U2. The left side of the RTC is next to the SRAM chip U9.<br />
You can do this on the component side or the soldering side of the
board.<br />
<br />
Power Gemini on/off. Wait. The CMOS resets should be gone.<br />
<br />
3) Remove R38 to save Li battery power. Check again.<br />
<br />
I've tested this modification with three different boards, one of them
had<br />
CMOS Resets. All work fine.<br />
<br />
René<br />
<br />
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