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.