Thanks for the responses.
Some fairly inexpensive radio transceivers ( RFM22B or the SIM20 433 MHz, or the 2.4 GHz RFD21733 ) can be connected as a mesh with multiroutes, aknowledge, and autoresend.
I get 500m from the SIM20 outdoors, but it might be better using the 2.4 GHz does WiFi work OK in the factory ? its basically the same frequency.
A standard RF circuit will not work in the environment I plan to implement. Have you seen the inside of your standard cereal factory? Think of all the motors that drive the lines and multiply their HP by around 30-600 and you get what I'm working in. The factory manufactures puzzles so we have a large amount of motors and controls running an this will be the first arduino ever present in the factory. Almost all the systems there are industrial-grade PLC's from Allem Bradley or Mitsubishi.
What is the spreadsheet for? I mean, what calculations is it performing and what is being done with the results?
Although you've specified that the results must be displayed in a spreadsheet, use of a spreadsheet is a solution not a requirement; the fact you're also asking for 'live' updates make me suspect the spreadsheet is not actually suitable for you. What is the actual requirement here?
Do you want a tabular display of the counters in some order? Over some period? Any of that user-defined? Charts of the rate of change or absolute values over time? The real requirements will imply the most appropriate way to store and present the data, and it may not be a spreadsheet.
My dad wants it in spreadsheet because that's what his employees know how to manipulate. He wants it to be user friendly. I told him repeatedly that Spreadsheet isn't designed for this stuff, especially with it being live. I'm thinking I will have to make a web interface that the arduinos link into with actual live data rather than programming a batch file to reopen a spreadsheet file every 5 minutes. Just another thought, if I got a Mux shield linked to an arduino and connected that to the PC, would that be about ideal for something like this or would it be more of a hassle to do that? I'm thinking of how hard it will be to integrate all the connections from the different arduinos to one page.
Seriously though, has anyone modulated laser pointers? and what range is possible? Of course there would be environmental interference from rain and mist, but I have a specific project I want to test sometime.
Lazer pointers have been modulated before with an extremely simple circuit containing an op-amp and an audio transformer connected to the lazer. I tried it with some success. It would have been better if I had an op-amp though. The range was fairly limited since I couldn't keep it aimed correctly for more than 10 minutes. I have heard of some people using small telescopes with a photoresistor/photodiode connected to the eyepiece. They would take a light bulb like you would find in a scrolling billboard with the light grids and turn it on and off with amps designed for speakers. They were successful at transmitting audio with a half-decent quality of sound.
And a side note, my dad is going by Radioshack to get an arduino for me to start learning. I already have a breadboard so no issues there.