Requirements

The purpose of this system is to understand the local heat experience on various parts of the MIT campus. Brian Goldberg's presentation from Lecture 2 is available to review.

Based on this, a starting set of requirements for the system are:

1. It should accurately measure the air temperature and humidity, with dynamics appropriate for the use case.***
2. It should measure ground surface temperature, with dynamics appropriate for the use case.*
3. It should operate without being connected to line voltage.***
4. It should be portable and able to be set up by an average person in a variety of outdoor environments on the MIT campus, including on a tripod or attached to poles of various dimensions.***
5. It should be able to be physically attached to a HOBO MX2302A data logger.*
6. It should report faults, such as battery failure, falling, vandalism, etc.**
7. It should be as inexpensive as possible.***
8. Data from a sensor node should be able to be tied to a location.***
9. It should maintain privacy. ***
10. It should operate independently without user intervention for 3+ months.***
11. It should be rugged and able to withstand a summertime Boston-area environment (heat, rain, wind and curious people). ***
12. Multiple systems should be able to be used simultaneously. ***
13. It should engage with the community.**
14. The system should present the information on a dashboard (with real-time data outputs to a dashboard if possible), and also allow downloading of raw data.***

There is a FAQ at the end of this document that might be useful.

System architecture

To get a bit of a head start, below is the system architecture that teams adopted last year. It's a good way to start, though you are by no means constrained to doing it this way. In any case, you'll have to adapt for this year's needs to work with two partners.

Specifications and Testing

A key team metric is to develop specifications along with a plan to test (or verify) that your system meets those specifications. We'll provide a draft testing plan, but the specs are up to you, and you'll want to refine the testing plan. You will be able to consult with staff and with mentors on this.

Given that this is a HW/SW system, we can anticipate specifications falling into the following classes:

• Financial
• Regulatory
• Industrial design
• Environmental resistance
• Engineering
• Security & Privacy
• Packaging
• Installation and servicing

Remember the two most important things about specifications: 1) have a process, and 2) write them down!. They are subject to update in our iterative process.

Every specification should be backed up with a testing plan for how you will demonstrate that your system achieves that spec. The testing plan should be detailed, quantitative, and verifiable. It is as important as the spec!

Here are some things to think about for different parts:

Financial

• We are not selling these systems to our partner, so one may think that cost doesn't matter. But MITOS is really interested in distributing these widely. So something with a BOM of 20USD is going to be more powerful than one with a BOM of 100USD.

• Our time to market is dictated by our class schedule.

Regulatory

• There's going to be communications here, so some regulatory requirements.
• The HW node should be able to withstand outdoor exposure. Boston is hot and wet during the summer!

Industrial design

• Consider how these systems will be mounted. We need a variety of mounts: primarily on a tripod, but also to a pole, and so on.
• For size and weight, smaller/lighter is better, of course. A handheld device is better than toaster-sized is better than a microwave-sized.

Environmental

• Think about that outdoor exposure.

Engineering

Sensors

• RH/T should be easy to specify and measure...but really hard to measure accurately. There's a reason that professional-grade weather stations cost $1000s of dollars. It's because it's really hard to measure air temperature. Usually people use an elaborate (expensive) shield to do this. But you can't afford that. Can you do something with a mix of HW and SW to get good accuracy? This company has a way of compensating for solar radiation using sensors and data science, as described in this video.
• There are several ways to measure sun exposure.
• Likewise, there are several non-contact temperature sensors that you can integrate into your system. That said, these are pricey, so you'll have to decide whether it's worth the BOM.
• It's up to you if you want to add an air quality sensor, or other additional environmental sensors.

Compute

• We recommend sticking with the ESP32-C3 that we introduced in lab01. You can go to a different MCU in the ESP32 family if you think you need different specs/cost. You can even go to a different MCU family, or even a SBC, but there will be less help from staff. Up to you!

Comms

• WiFi is present everywhere on campus, sort of. Sometimes it's hard to get at in the nooks and crannies.
• Cellular is another option. It adds to BOM and complexity, but makes you able to access more outdoor locations.
• LoRa is another option for low-power long-distance comms.

Energy management

• There's no A/C line voltage around the HW nodes, nor is there a nice 5V USB port to connect to.
• There is alot of sun.
• And you can use a battery, of course.
• Weather changes slowly. Even occupancy is slow from the standpoint of a microcontroller that runs at 160 MHz. So, you can spend most of your time sleeping if you want.

Firmware

• What does the MCU need to do in this system? You'll want to architect the firmware so that it is easy for team members to work on different sections, easy to debug, and so on.
• The MCU will most definitely need to sleep in order to meet energy budget. See previous...

Server & analytics

• Since we're setting up a server in the psets, we recommend using that approach here. But you're not obligated to do so.

• It will be useful to overlay your data on a map.

Web front-end

• You'll want to both visualize the data, as well as make it available for use by partners.

Security and Privacy

• These systems are going to be deployed in the wild. Residents are important stakeholders here. At MIT, there will be curious students and sometimes members of the public.

Packaging, installation, and servicing

• How will the HW node be installed, turned on, commisioned, and debugged (which will certainly be needed)?
• We'd like to set up that HW node in May and leave it out till September or October, ideally without someone needing to attend to it.

Resources

• Lauren Futami's MS thesis on the MITOS systems

FAQ

Q: What areas of campus should we target for monitoring?

It would be good to start with the ones we measured last year, so we start to accumulate longitudinal data.

Q: Are there any plans to expand to Cambridge?

Yes, there have been conservations with the City of Cambridge, and if these sensors work and are relatively inexpensive there could be a pretty big uptake.

Q: How can we evaluate the accuracy of our system? Is there a gold-standard we can compare to?

This is critical. The gold standard is a research-grade weather station. We believe that there is one on the Green building and another at the MIT Sailing Pavilion. It would be great to use one of those to calibrate your systems.

Q: Why were last year's measurements higher than expected?

Partly it could be due to actual elevated temperatures in a heat island. But it is also due in part to solar heat gain of the device itself.

Q: Do materials affect temperature results?

Most certainly. Different materials absorb/reflect incident solar radiation.

Q: What does privacy mean here?

Privacy just means that you don't want to do anything that would identify people. It's probably a super-easy requirement to meet. Take the "W".

Q: What connectivity can we expect?

Theoretically the MIT campus has widespread WiFi. But it can be spotty outdoors, so this requires some thought.

Q: What was last year's prototype BOM?

Ask Srinidh or Hasan. They have the complete breakdown. But it was around $300.

Q: How did weather affect last year's units?

The units survived being outdoors all summer. However, there were periodic failures that we weren't able to debug, which could be due to environmental exposure (we're not sure). We also observed (though not 100% confirmed) some condensation in the units, but again was difficult to tell.

Q: Why not create a device that attaches to a Hobo and just relays the Hobo data to a basestation

You could, but then all you're using from the Hobo is the RH/T sensor, which is about a $1. So it's probably cheaper to build your own system.

Q: What data do you want to see on the dashboard?

• Basic map with locations of each sensor
• Reporting/visualization of daily averages for each sensor for temperature and heat index (i.e. day time average; night time average; 3pm-6pm average; 3am-6am average)
• Include temp reporting from MIT sailing pavilion
• Reporting intervals every 30 mins or so

Q: How will you use the data?

• Potential uses include:
• Understand how popular outdoor spaces on campus experience heat measured by temperature and heat index
• Understand how outdoor spaces on campus compare to National Weather Service temp reporting (via weather apps for Cambridge)
• Identify places on campus that might require additional heat relief/shading during summer months
• Raise awareness among students and MIT community about the increasing frequency of extreme heat and the importance of understanding it’s potential impacts on people
• Inform actions that MIT and City of Cambridge can take to provide heat relief (i.e. develop indoor/outdoor cool spots for people) and inform longer term changes to public spaces so that they can stay cooler during extreme heat

Q: If we also use these monitors in the winter, are there specific issues to be aware of in that environment? Or are there different things to measure (e.g., wind chill)?

• Monitors will need to be stable and affixed to something that would not get easily knocked over and rest on the ground in snow and ice
• While we’re most concerned about the increasing frequency of extreme heat resulting from a changing climate, a changing climate can also bring more swings of cold days followed by warm days. Seeing days where temps swing wildly back and forth is not common in New England during winter. Seeing this here on campus could help visualize climate change here on campus.