Beginner's question (re LPT1)

[swa]

Hello

I have an idea I am ready to implement, but I won't go ahead until I know whether it's feasible. I would appreciate some comments regarding whether it might work.

The idea is to hook up LPT1 to the keyboard matrix of a non-MIDI musical keyboard. Now, each key on the musical keyboard works by making a connection when the key is pressed. The sound chip works out which key(s) is being pressed, by determining which of 6 data lines is set or not-set (i.e. 1 or 0). The player of the instrument holds down a key for however long, and a sound of the appropriate pitch is generated until the key is released.

I intend to simply wire in a connection to LPT1, to the 6 data lines directly, i.e. without relays/reed switches, and then remotely operate the keyboard by writing a program that sends a bitstream to whichever data line I want. I imagine that given it's a 6-volt unit, then sending fast 5-volt pulses directly into the data line for x length of time should close the circuit in the same way as pressing a key.

What do you think? Is this mad or might it work?

Thanks

 

[cyb0rg777]

Sounds like this can all be done in software with some wiring.
Programming a legacy parallel port is easy .
A newer bidirectional port is harder.
A sound card used to be easy too depending on the system you are using.
I haven't done it recently.
I'm sure if you can write the program it will work.

 

[swa]

Great! I'll give it a shot. I can write the program with a tracker-style interface. My old laptop runs Win95 and has a true parallel port, so it should be OK. Relays would definitely work but if it can be done without, then so much the better.

 

[mramos1]

I imagine that given it's a 6-volt unit, then sending fast 5-volt pulses directly
Thanks

The LPT1 is TTL I believe to 5V out. You will not want to go two fast or you might not hear the sound. If the direct wiring does not work, you can drive the keys to ground with 2 resistors and a transistor. You are sure the sound chip is 5 volts in?

 

[swa]

Yes I'm fairly sure the chip's input is around the 5/6-volt mark. In case it doesn't work, can you please elaborate more about what you mean by using 2 resistors and a transistor to take each line to ground?