Ive got these microswitches with levers. Ive got these gravity fed box racks. When the box is on the switch lever, its "off". When the box slides off it, the switch sends a signal through an arduino "thing" to our ordering software. Ill need HUNDREDS of these setups. One for each rack with boxes. What would you use for the controller? Possible? Cheap enough?
If you can wire them all together, you could use few digital IO expansion modules and one Esp32. About 25 bucks all together for 100 switches.
By the way, your post title is little bit misleading.. 
Watch your design very carefully! Microswitches are famous for bouncing connections on closing. If you wire them to OPEN on pressure, you will have better luck!
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This sounds line an industrial environment, if so I would not use an Arduino out of the box, they will need protection from EMI, RF, Transient etc interference. It would be easy enough to build it in the lab and it will work but when getting into the industrial arena with all the electrical noise it will be problematic.
If you do not have the skill consider a PLC, they are designed for this environment. The only wire allowed out of the Arduino into the field is the ground, all of the rest must be buffered/isolated from the Arduino. I like to run at least one mA at 24VDC through these type of switches as they are not rated for dry contact switching. This should get you started.
If it is a time critical process, diy microswitches + arduino is not probably the way to go. Like gilshulz wrote, professional PLC with tested components for interferences should be used.
On the other hand, from description I could immaginate that the process is not time critical. Something like "when the last box is gone, connect to wifi and send a note". In that case microcontroller has plenty of time to filter the noise an triple check that the switch is surely open.
Also one should consider mechanical wear of the switches if they are switching on and off repeatedly. Digital IR-sensors are cheap alternative.
Thanks. But our racks are in about 1/2 million sq ft of space. Ill keep digging.
But how is it misleading. Im just dabbling in this so I dont know the exact things to say...
Well first you need to find out the exact amount. If it's 100, it may work via 100 WiFi connections. If it's 500 then WiFi would be a disaster.
Next you need to find out how far apart the racks are and if wired communications would be feasible
That is a lot of area, If the building is square it is about 700' per side. Are these switches located in groups and/or are they relative close to each other. This is a major project and I am assuming lots of 3 phase motors in the building with contactors controlling them. Also electronically controlled motors. Have you considered making some custom Circuit boards?
We are all just guessing here. To recommend an ideal solution one needs to know all the factors. May be wired, may be wireless, may be even battery powered. Most important factor is how time critical it is. Some safety switch has to work reliably within a millisecond to prevent injury. Or CNC machine having interferences for few milliseconds could destroy the workpiece or the tool itself. On the other hand, one second is a lifetime for microcontroller, time enough to send hundreds of signals or filter out interferences.
Anyway if your application is not safety related I encourage you to go on with an open source system, keep your dirty cheap spare parts at your office and replace when needed by yourself. Most of companies buy proprietary systems even for stupid simple solutions and after they need to call technician every time there is an issue, waiting for spares to arrive, if still available... And the production line is standing still for days.
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