To trigger a device input I need a voltage of at least 18 V. One can surely solve this with an external voltage source and a transistor but is there also a way to boost the GPIO that high without an additional voltage source? I'd prefer a readymade solution (boost converter, villard/greinacher on extension board). I just need a voltage slope to shoot the trigger - no power required (I <1 mA).
"No current required" calls in my opinion for a charge pump. This is the concept typically used for RS-232 drivers/transceivers. Actually if 15 V are sufficient (and not 18 V) as written, something like the MAX232 might be the thing to go with.
Charge pump with a toggled GPIO however should also be possible. I'd look into this.