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I am trying to implement this, but there are a few problems I am facing..

  1. Should I connect PIN 5 of DB9 to Earth ground or the negative pin of the source.
  2. When the serial Rx and Tx cables are attached to the MAX232, loopback in occurring. I have checked, there is no short in the breadboard. How is the data coming back? Yes the 'echo' is off in hyperterminal.
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  • \$\begingroup\$ yes, i found the circuit in the net. The PIN 15 is connected to the negative pin of the source. I am using a voltage regulator to get 5 volts. \$\endgroup\$ – Arjob Mukherjee Apr 3 '13 at 10:00
  • \$\begingroup\$ OK, wasn't sure of your level of experience and thought it might have been missed. Normally pin 5 would go to ground as above which would be the same as ground on the regulator and the ground of the input. When you say negative pin I assume you mean the negative terminal of a battery for example? I wasn't really clear on why you mention ground and negative pin as something different. If AC powered you definitely don't want anything going to the mains ground. \$\endgroup\$ – PeterJ Apr 3 '13 at 10:06
  • \$\begingroup\$ Yes, negative pin is the negative terminal. But then why is the MAX232 doing loopback, even when I disconnect the microcontroller. \$\endgroup\$ – Arjob Mukherjee Apr 3 '13 at 10:14
  • \$\begingroup\$ Not 100% sure, but make sure pin 5 does go to ground and then as a first step with the micro removed try putting pin 10 to ground to make sure the transmit input is not floating and possibly picking up the received the data. \$\endgroup\$ – PeterJ Apr 3 '13 at 10:23
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Have a look at this: -

enter image description here

Pin 2 is shown as the input receive line to the PC and this means you connect this line to your 232 transmit output. At the moment your diagram shows it connected to your receive input.

I'm not saying it'll fix your "loopback" problem - that may be connected to this wiring error so try this first.

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Pin 2 of rs232 should be connected to pin 7 of max232 and 3 to 8 respectively. the given fig has errors. u can consider both cases from the fig, they may have drawn it in correct sense.

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