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I have a Linksprite RS232 v2 adapter (which uses a MAX232 chip), as per this image. I have soldered on the headers and tested the pins to make sure there are no solder bridges. I have set the jumpers so that D2 is set to TX and D3 to RX. However, I can't establish comms through the device using the Software Serial library, regardless of how I set the jumpers. (Real Term doesn't show me anything when a USB-to-Serial adapter is connected. However, if I change the baud rate to 9600, I get about 5 bytes of 0x00, then nothing.)

If I disconnect the shield from the Arduino board then supply 5V to pin 2 or 3 (from an Arduino) and connect pin 5 of the DB/E9 to the Arduino's GND, I get output from both pins 2 and 3 (RX/TX) on the DB/E9 (regardless of which pin on the board is powered). The voltage between pins 2 and 3 on the connector differs by ~0.1V. Is this normal or is my circuit faulty? How do I test the continuity of the board/connector and diagnose and fix the fault?

In case it's of any relevance, I'm using an Uno with an SMD chip.

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    Do you have an oscilloscope, or logic analyzer, or more than one Arduino? If you only have a DVM, with jumpers off run a sketch that toggles different digital pins at about .5 Hz, and verify that that shows up ok on pins of J2 on the shield. – James Waldby - jwpat7 Mar 25 '17 at 5:08
  • I don't have an oscilloscope or logic analyser (or know how to use one). I do have a DT830B multimeter and multiple boards (Uno R3, Leonardo R3, Mega 2560 R3). – Agi Hammerthief Mar 25 '17 at 10:59
  • It turns out that the ATMega328P-PU chip on the Uno I was using is damaged. I will try again with a different board and see if the problem persists. – Agi Hammerthief Mar 25 '17 at 11:55
  • @JamesWaldby-jwpat7 Thank you for the suggestion. I managed to get access to an oscilloscope and test the shield with a different board. It helped me diagnose that the RS232 shield is non-functional. – Agi Hammerthief May 4 '17 at 21:10

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