Pi vs Arduino vs NodeMCU vs ???

It's official - the Internet of Things has a lot of, um... things. So many options! Consider this: my friend and I are working on a weather station. Of course, it can't just be a simple weather station, it eventually needs to be a cluster of stations that can be used to measure differences in micro-climates. More on that later, LOL.

The initial goal is to put a weather station on a roof, without wires. With so many little devices, the question is simple: which is the right device for the job?

• I started in on this the other day when I started messing around with the GPIO pins on the Pi. In about 10 min, I was reading in temp and barometric pressure data and thought "Dang, that's easy!". The Pi is awfully powerful and, now with the Pi 3, wifi-enabled.
• And then there's NodeMCU. Very cool little wifi-enabled device that can take signal on a variety of analog, digital and serial-dedicated pins. And then it can run Lua to actually form that data into "IoT" capable packages, like HTML pages or JSON packets. Finally, it can be a rudimentary http server, so data can be retrieved (conversely it could be written as a client, to push data directly into the cloud). Seemed to me to be the perfect solution.
• My friend Chuck is a strong advocate for using the Pi with an Arduino on a Pi alamode board. The arduino collects the data, the alamode board pushes that data into the Pi, and the Pi processes it.

My take? I see four viable solutions for getting the data off the Sparkfun weather shield and into "a consuming sink" such as the cloud, a data aggregator like a database, or published to the web.

1. Weathershield to Pi via GPIO interface
2. Weathershield to Pi via Arduino
3. Weathershield to NodeMCU
4. Weathershield to Arduino with WiFi chip

Each solution has advantages and disadvantages, and that's what we're doing to explore now.

Weather Shield to Pi via GPIO

This is an elegant solution - it requires the Weather Shield, some connecting wires, and a Raspberry Pi. It's elegant in that there are few moving parts - wire it up, good to go. Right? Wrong. Not all of the Weather Shield components seem to have Python libraries available, which means the coding would need to be done in C. Not impossible, but not necessarily straightforward.

Acquisition cost: 

• Weather Shield: $39.95 + shipping
• Raspberry Pi 3: $35.95 + shipping
• Misc parts: $5
• Total: $80

Development effort:

• Moderate to high

Weather Shield to Pi via Arduino

This is the easiest solution to build, frankly. The weather shield runs great on the Arduino, all sorts of libraries and sample code abound on the Internet. 

Acquisition cost:

• Weather Shield: $39.95 + shipping
• Raspberry Pi 3: $35.95 + shipping
• Raspberry Pi Alameda: $35.00 + shipping
• Misc parts: $5
• Total: $115 + shipping

Weather Shield to NodeMCU

By far the most elegant solution, holy cow... Suspend disbelief briefly and take a walk with me... You have a weather station on the roof, which feeds data into a Sparkfun weather shield. That shield, in turn, feeds data into a NodeMCU chip - tiny, quarter-size chip with wifi on it. The NodeMCU does three things: 1) it pushes the data to a cloud service, every N minutes; 2) it serves the data up via JSON string to anyone on the local network, and 3) it serves up data via formatted HTML on the local network. Awfully cool, and the cost? Nominal.

What's the issue? Simple - the libraries for the components of the weather shield only exist in part, and it's a process of porting them to Lua to make them work. The other problem: NodeMCU only has a single analog pin, whereas the weather board uses three or four.

--> Caveat: the NodeMCU *can* be programmed via Arduino, using Arduino libraries. I need to look into this more; not sure if there's enough memory to do it, though. And the Arduino environment has convoluted support for outputting HTML. I think I just need an afternoon to figure it out though. But still, the bottom line is it's not the right tool for this job.

Acquisition cost:

• Weather Shield: $39.95 + shipping
• NodeMCU: $15.00 + shipping
• Total: $55 + shipping

Weather Shield to Arduino with Wifi Chip

This solution is honestly just a variant on the above solution - the weather shield speaks to an Arduino (great library support) and the Arduino uses a Wifi chip on a shield to publish the data. 

Slightly more expensive than the standalone NodeMCU solution:

• Weather Shield: $39.95 + shipping
• Arduino Uno $24.95 + shipping
• Ada fruit Huzzah wireless shield: $39.95 plus shipping
• Total: $105 + shipping

Summary

The cheapest possible solution, using the Weather Shield with NodeMCU, is not possible because NodeMCU only has a single analog pin and the weather shield needs multiple. That doesn't mean NodeMCU isn't a useful tool - I have a couple of other projects it might be perfect for. It does mean, however, that it's the wrong tool for this job.

From a financial perspective, the lowest cost solution is the Weather Shield plus the Raspberry Pi. It presents some problems - probably not insurmountable, but there'll be some effort to integrate the Weather Shield natively into Pi via Python or C. The time spent may not be worth the money saved over the alternatives (which both make use of an Arduino to read and interpret results).

So a little research is needed, to see how well the Pi can work with the Weather Shield's components. That's how to solve this specific application, but making a global rule overall? Globally I think it's easy to say that the NodeMCU is a low-cost solution but will almost alway have a steep implementation curve, at least until the dev community matures and catches up with Arduino. Overall from a sheer convenience perspective, the best solution is either 1) Arduino with Pi or 2) Arduino with wireless.

Bottom line: my buddy Chuck is right. When I insisted I take some time to look into building this solution with something other than Arduino, he told me I was wasting my time. I *was* right in that it would be more elegant, but he is right from a practical perspective. Everything is just "there" and ready to use, if Arduino plays a role in the solution.