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I have connected a MAX232 chip for RS232 communication with my Arduino. The chip input is connected to Arduino Tx and it is getting power from external 3.3 volt dc power source.

My Arduino is also getting power from 12 volt DC external power source.

While I connect and start the device, the PC is not getting any data until I reboot the MAX232.

How do I make a robust setup so that after I turn the powers on, it starts transmitting. Even if connection to my PC has been lost.

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    MAX232 is not a microprocessor, and does not require initialization. It's really just an inverting level converter. Can you show a schematic of how you have it connected? Also, the typical MAX232 is a 5V part, so 3.3V powering it won't be reliable. – jose can u c Sep 3 '18 at 12:23
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    Agreed - for 3.3V operation you need to use the MAX3232. – Majenko Sep 3 '18 at 12:42
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Datasheet for MAX232

Section 7.3 Recommended Operating Conditions VCC Supply voltage

MIN=4.5, NOM=5, MAX=5.5 (V)

The MAX232 has a minimum supply voltage of 4.5V, typically expecting 5V.

There are other alternatives, such as the MAX3232, which supports either 3.3V or 5V supply voltage.

  • Thanks, I also found that error in datasheet about 5 volt power. But is there any startup sequence? – Moithil Biswas Sep 4 '18 at 6:35
  • Say i have to turn 12 volt power first, then 3.3 and then connect it to the pc. Is there any logic behind proper startup sequence? I am using different power sources. – Moithil Biswas Sep 4 '18 at 6:36
  • The MAX232 chip has no 12V supply. There is no startup sequence. – jose can u c Sep 4 '18 at 10:14
  • I have tried whatever I found here, but still I am unable to send data from Arduino to pc via MAX232. I have only connected the TX line, ground from Arduino to MAX232 chip, thats what i need actually (Arduino here is not supposed to get any data). – Moithil Biswas Sep 5 '18 at 4:02
  • All common grounds are okay. Power lines are okay. Connections are too properly done. – Moithil Biswas Sep 5 '18 at 4:03

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