dry contact switching for synthesizer bank buttons

[CHH]

I'd like to control the "bank" and "patch" buttons on my pre-midi electronic synthesizers from my laptop by tapping onto the switch contact leads from the buttons that change the bank/patch selections on the control panel of the keyboard. These are just momentary contact buttons that are soldered onto one of the circuit boards. I have two identical keyboards. Each has 13 buttons I'd like to control, some of which need to be pressed simultaneously. My laptop has a 9-pin serial port, a USP port, and a PS-2 port. Long ago, a friend was going to do this for my by using computer-controlled SCR's, I believe, but I have no idea how to accomplish this. I'm not looking for detailed instructions, necessarily, but would appreciate a place to look for answers/diagrams/chip types, etc.
Thanks.............

 

[Dialtone]

You could use decoder chips wired to the parallel port output data leads. Using 2- 74ls154 decoder chips would get you direct control of 32 output leads in 2 seperate banks of 16 each. If you needed more than 2 at a time control, you could use 1 more driven by the printer port control leads. , or split the 8 data bits out using 2 in 4 out decoder chips.
To control it, you just write a data byte to the port and the decoder translates the bit pattern into the appropriate output lead(s). What you do from there depends on the exact interface needed at the switches.
Dialtone