So this will be quite a fun bit! And we [yes I know it's just me lol] get started on this quite quickly! What kind of sensors will we need? Will we want to record all the sensor data to a mySQL database? We'll want to to output sensor data to a screen locally, And also output to a a smart phone too. And a not-smart phone via SMS. I imagine we can do something with Microsoft Azure IOT platform too.
Anyway, so the zones we have which require sensors are:
Lighting zone, i.e. LED lighting
Plant zone, i.e. the leaves and stems. Would also include the baskets the plants are housed in
Root zone, i.e. yup the roots which are exposed in this zone
Well, for the plant zone we need to monitor gases, and temperature. We could also take images of the plant leaves. We don't need to monitor light since we know what the LEDs will output. Perhaps we should monitor relative humidity here?
For the root zone, we need to again monitor gases. Although since the plant-zone and root-zone are not hermetically sealed the gases are going to be the same. We mostly need to monitor relative humidity. And temperature too.
For the water-supply zone, we need to monitor the water-level in the reservoir, pH in the reservoir, and TDS (total dissolved solids) in the reservoir too.
Anyway, so we can get this all prototyped fairly easily!
Now the hardware for this, I think, is going to be a GrovePi+ HAT for the Raspberry Pi, and using the Grove sensors. They have a really extensive range of gas sensors [see https://wiki.seeedstudio.com/Sensor_gas/]
Sprayers: Well I've noted 'Spray Jet' with 0.016" Orifice [https://aeroponics.com/secure/shop/item.aspx?itemid=85] that should be good for 5-25 micron droplets. These can be in nylon, or brass from what I've seen. Now idea how I can even measure droplet size!. I'll give those a try since they are kinda cheap !
So the primary components of an aeroponics-based vertical farm:
LED-lighting array comprising LEDs of varying wavelengths
NB. needs to be isolated from the plant and root zones, since we don't want the electronics to get wet! Perhaps with plastic or glass as a barrier.
Mounts for the plants, with supply of required gas mix. Sensors specific to this zone.
Here the roots are exposed to components which will deliver water and nutrients and required gas mix. Sensors specific to this zone.
In order to supply water droplets of required size (i.e. 5-50 microns per [need study ref is this the best size] we would need a high-pressure delivery system for the water. This is I think to most complex component, and has a few different possible designs (each with positives and negatives to investigate)
Water and nutrient reservoir
High-pressure ~100psi water-pump. This would be an off-shelf component of the system
Filtration upstream or downstream of the pump? Or is it actually upstream of the reservoir?
Pre-pressurized accumulator tank. The reason being the pump will take some time to get to required pressure, so this prevents us hitting the roots with droplets that are too large. This is one of the components I'm a bit unhappy with. Since off-shelf will mostly be steel, and if they go over their pressure tolerances (e.g. pressure-relief valve fails, poor maintenance, problems with pump) they may explode! The off-shelf tanks can also be made from nylon, and I have heard reports of DIY tanks being built from PET bottles. So this bit will need careful investigation.
Solenoids for switching the spray nozzles on/off
Spray nozzles with holes of required diameter. These can be purchased easily, or can be 3d printed I guess?
There is actually an alternative to using high-pressure for producing droplets of required size! Loosely referred to as fogonomics. So would use ultrasonic atomizers (e.g. https://www.amazon.com/dp/B073322QF8/ amazon link) to get required droplet size from a water reservoir. Perhaps with wicks from the water reservoir to the atomizer which could be then mounted in the ROOT-ZONE? An issue with this is difficulty of cleaning the atomizers, and would the nutrients get through them ok? It's kinda easy to screw off a spray nozzle and clean it manually. But these not so much. There is an idea to automatically clean them I have noticed, and will investigate. The positives of this method are being we don't need to worry about the pre-pressurized accumulator tank anymore and don't need a high-pressure pump.