Robot Brain: Build a single board computer in an evening

Step 4 Wire up a serial cable

If you go back to step 2 you can see the serial cable in the picture. There are three parts to this:

1) My extension lead that comes from the back of the PC. This is the rainbow cable. I built it the same way as the programmer lead extension cable except that this one uses a D9 IDC plug and socket. It is really useful not to have to keep reaching behind the computer all the time. The extension lead has a female at one end and a male at the other.

2) A null modem. This is a female to female connection. I got the circuit from here http://www.beyondlogic.org/serial/serial.htm (scroll down a bit). Essentially, a null modem joins pin 7 and 8, joins pins 1,4,6 and swaps pins 2 and 3 over. The 9 pin connection then becomes a 3 wire connection -ground, transmit data and receive data. It kind of simplifies RS232.

3) A 10 pin header on the board to a D9 male connector. More about this on the next page.

On the schematic, the male D9 on the left connects to the PC. The null modem is a female to female connection with the connections in the plugs. I could have wired all this with a lot less plugs, but I'll be using the null modem in other projects.