Gemini 1 mods
Recommend modification to Gemini-1 boards from uses Group
message.  This mod only applies to boards that use the RJ45 connectors for motor connectors.

Gemini's SRAM is not only used to store user catalogues and the observation
logs, but also an amount of parameters and matrices used for the modelling
algorithm. So it has a size of 128 kByte and is accessed (also for writing)
very often, far exceeding size and reprogramming life time of an EEPROM.

Normally, the Li CR2032 battery should last at least one year and should
keep the SRAM content safe and the RTC running. If CMOS Resets occur after
some minutes even with a fresh battery or battery lifetime is significantly
shorter than one year, I recommend the following patch for the electronically

  1. Buy a small 39k resistor (with wires, not SMD)
  2. Remove all power and battery.
  3. Solder the resistor between pin 2 (the second from above at the left side)
    and pin 9 (the down most at the left side) of the EPSON real time clock
    chip labeled U2. The left side of the RTC is next to the SRAM chip U9. You can do this on the component side or the soldering side of the board.
  4. Put Battery back. Hook up power.
  5. Power Gemini on/off. Wait. The CMOS resets should be gone.
  6. Remove battery again and power.
  7. Remove R38 to save Li battery power.
  8. Put battery and power back and Power Gemini on/off. Check again for CMOS resets. They should be gone.

I've tested this modification with three different boards, one of them had
CMOS Resets. All work fine.


Click on image to see larger view.
Picture courtsey of Brendan