See picture below on how to connect Arduino to Speak and Spell
Updated (31-12-2010) i forgot the Input on D4 for CNTL8) :
Crappy Schematics :
Not sure if the -12V is needed has the PMOS should have Pulldown Resistor inside.
The Switch is here to launch the Speech command, because the Midi is not implemented yet.
Explanation on the command bus (with the Transistors) :
When Arduino Pin is on 0, the Transistors will conduct and there will be a 1 on the Bus Pin,when Arduino Pin is on 1, Transistor will stop conducting and there will be a -12 on S&S bus
On CNTL1, there is a Diode connected to input pin 4, i've put this here because when the S&S is on Speech the CNTL1 is high and you need to wait until speech is done.
By pressing ON, ON, GO. This leaves only the cursor on, which causes CNTL 8 to periodically go high
see below the connections inside S&S :