Rylan............. love the idea........... the drip from your valve could be software demanded, without the use of arduino. You simply have a light dependent resistor or photocell at a know location on the side of the tank and above the resin. This location would be known and calibrated. Every time the software wants a drip, it would switch the laser off, move the galvos, so the laser pointed at the LDR/photocell and then switch the laser on. This pulse of light could be used to switch a transistor on to deliver the current to your valve. You could demand a number of drips, one after the other by pulsing the laser on and off if required, or demanding a single drip...... it's totally flexible. This solution requires no digital components, just a single transistor and LDR and a reserved switching location in 3d space. The software would have a demand drip function, which would handle firing at the ldr on the side of the tank. The only parameter you would pass is number of drips required (demand-drip(n)).