Comment by exmadscientist

True enough, but it turns out you can't fire a nozzle with a 50% duty cycle TTL signal... it's more complicated than that. More analog. More annoying.

Most of my knowledge here comes from very peripheral involvement with a project to repurpose an inkjet printhead to do Something Else™ (sorry, NDA here). The printhead high priests just scoffed at any kind of software control over the firing process, and that was that.