This question is intentionally rather open ended, and potentially opinion based, but it is intended to act as a catch-all for the questions on how to select a device for a sensor/endpoint. Any question which intends to be more specific would need to start with assumptions about all of these points.

Question: In addition to the points below, how would someone go about selecting a good device for the sensor/endpoint part of an IoT system?

There are already good questions 1, 2, 3 on how to select specific devices for a well-defined application, and questions that address some of the points below in detail.

There are a number of clear factors which will help to determine which devices are suitable for a particular application. In the end, there are likely to be many good choices, and no obvious 'best'.

  • Communications. A sensor will usually rely on a wireless interface, sometimes a combined power/signal wired interface might be appropriate. Depending on the application, this might be well defined, or there might be some flexability. Communication can be built-in, or a peripheral depending on how good a fit the other parameters are. Depending on the device deployment, there is a scale of roughly increasing cost/range from wired (Ethernet, serial, USB), short range (BlueTooth, WiFi and mesh variants), developed areas (SMS, LoRaWan, NB-IoT), remote (satellite). Bandwidth and latency also factor into the choice of communication protocol. Note that often the communications parameters are fairly well defined up-front before worrying about specific device selection.

  • Processing power. Some sensors are just taking input values and generating packets, others are doing complex signal analysis (face recognition for example). Some communication protocols need a reasonable processing power, so result in devices which have a small (but useful) amount of left-over processing power.

  • Device or Module Modules have the advantage of providing an off the shelf, pre-certified solution. They may also be cheap due to economy of scale. If you already need a custom PCB, a device might allow better optimisation.

  • Power Consumption If the sensor is battery powered, this will limit the communication choices, and also tends to suggest a device which will spend most of it's time in a deep sleep state (i.e. running a real-time embedded OS rather than Linux).

  • Power Source Related to consumption, but acting as a different type of constraint. Mains/battery/solar/harvesting are the obvious choices.

  • Security Often security can be ignored (for one off or evaluation projects). If security is important, what is the threat model? Are encryption accelerators important? Do you need a secure bootloader with the ability to prevent firmware roll-back, whilst at the same time allowing over-the-air firmware updates?

  • Peripherals If your sensor uses SPI, you need an SPI peripheral. If your sensor is a USB gadget, you need USB-on-the-go. For a high-end sensor, maybe you need a touch-screen display. Define the minimum set for your application. Memory sizes and external storage may also be relevant.

  • Production or Project There are economy of scale questions, availability, toolchain, example code, etc. issues that might affect the choice depending if this is a one-off project, a mock-up learning tool, or a full high volume production concept.

  • Coding Style Depending on your existing experience, migrating to a linux or mcu development environment might be a significant cost, might be necessary, or might be the reason for the project. Often you might prototype on a more powerful/flexible single-board computer, even if an optimised sensor/hub architecture would result in splitting the functionality between two devices.

  • Vendor There may sometimes be a specific reason to only consider devices from a specific vendor, but generally this is one of the most opinion based aspects of device selection. Free samples, good development boards etc. might be a factor here (although someone pays for this in the end).

  • Software Stack You may be set on using a specific software stack (maybe to integrate with a cloud provider), in which case there can be hardware requirements (RTC, TRNG), or you might just require a certain library to be available (TLS, COAP). Each RTOS will require certain features, Linux will require more (mmu specifically).

  • Thanks, Sean. As I said only yesterday on this question, we need a canonical question on how to choose a device and this looks like it. With regard to communications, I noted there a preference order of Ethernet, WiFi, SMS, satellite for data transmission. Can you work that into the question somehow? – Mawg Oct 11 at 8:38
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    @Mawg, how does that look? Hopefully the system will suggest this if people start asking something similar. All it needs is an answer or two now, with some more selection criteria. – Sean Houlihane Oct 11 at 9:02
  • That looks excellent - with one minor quibble (sorry). "global (satellite)", they are all "global". I use satellite in "remote" areas, where I don't even have coverage to send SMS. It's a good looking question (which basically answers itself :-) – Mawg Oct 11 at 9:09
  • "Power Consumption" - mains -> battery -> solar -> any others? – Mawg Oct 11 at 9:10
  • How about "software support"? Some implementations have requirements for certain software. This might be a superset requirement for "Coding Style" above. Otherwise, excellent overview. – Gambit Support Oct 11 at 12:52
up vote 1 down vote accepted

Let me answer this in a slightly frivolous way, better answers welcome.

After considering all the above, chose:

  • Something suitable from your existing hardware
  • Something nicely optimised for the application
  • Something you want to learn about
  • Something cheap enough, reliable enough and easy enough

Come next year, you might make a different choice for the same problem.

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