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I am scratching my head to figure out a possible soloution for this scenario:

I am developing a simple application using TI MSP430 microcontroller. The microcontrol part is powered by 2xAA batteries. I want to send/receive data from the chip to my PC's RS232 port.

I already made a level matching circuit by using MAX232N. My problem is, since the MSP430 is powered by 2xAA, it can not reach the +5 volt required for CMOS to RS232 conversion to happen, considering that the voltage from those batteries is around 2.8 if they are fresh and gradually drops down.

Can somone please point me into a good direction?

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  • \$\begingroup\$ Why don't you use a MAX3232? \$\endgroup\$ – starblue Dec 6 '12 at 19:57
  • \$\begingroup\$ If the serial communication is just for debugging, but is not going to be included in the release version: build a different PCB for the convertor, including the MAX, appropriate power supply and optocouplers that work with any supplied voltage. \$\endgroup\$ – Vorac Dec 7 '12 at 11:36
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There is no simple solution here. Really what you can do is either:

1) Use a different chip that can allow for lower voltages. Take at the list below: http://para.maximintegrated.com/en/results.mvp?fam=rs232&793=1.8|2.5|2.5%20to%203|3

2) Use some booster IC to bring up the voltage to 5V. Btw, the MSP430 won't tolerate 5V I/O very well, so you're better off using a 3.3V RS232 device at least.

Solution #1 in effect is #2 but more integrated.

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MAX3232 exactly for your purpose. uses charge pump caps to get higher voltage

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    \$\begingroup\$ This is the start of a worthwhile answer, but try writing in complete sentences. \$\endgroup\$ – Dave Tweed Apr 25 '13 at 16:20

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