$1 at the hardware store, not scary
also i'm not confident a soundcard that is not dc-coupled can do pulses... though i have no experience with this. if you check your output on a scope it's likely a very bouncy signal. the WW firmware would need to be tuned, or the input circuit on the frontend. you may be able to do a simple RC debouncer with a cap and resistor, but i can't really get you further into that.