I developed this TTL/RS232 module using a typical MAX232 chip. It is a RS-232 serial communiations transceiver with two transmit and two receive channels. It converts from TTL logic (0V=low, 5V=high) to RS-232 signals (approximately -10V to +10V in this case); see the datasheet for more specifics. The 6 pin header has 5V, GND, RX, TX, DTR, CTS. The 10 pin header includes all the DB-9 pins, with the DB-9 female connector attached via ribbon cable and socket. This model of the Maxim chip uses 0.1uF capacitors. I could have used the MAX233 which has is an extra 2 pins wide but doesn't need any added capacitors so is easier to work with. LEDs are included to show send/receive and cts/rts activity. Two of the resistors for the LEDs ended up on the reverse side of the board.