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I'm about to start an investigation about people movement after a surgery (walk basically). I would like to know where should I start to look for movement sensors (pedometer/accelerometer). This sensor basically has to be installed on the patient and has to monitor his movement.

I need something affordable, efficient, lightweight and non intrusive. I don't know where I should start to search for sensors.

This sensor also needs to be accessed from outside, for example: a custom iOS app that asks for the sensor information and store information on a database on the cloud.

The sensor has to be accessed via wireless (bluetooth or lte) or some kind of api.

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    This is a solved problem, it's a fitbit
    – hardillb
    Nov 2, 2017 at 17:02
  • That's not really. I need to access the sensor information from my own application, I can't access fitbit because is a propietary software. By the other hand, it is not affordable because every patient on the hospital should wear it and 80$ each sensor is so expensive.
    – Lechucico
    Nov 2, 2017 at 17:05
  • Then search for open step trackers, there are a huge number available from China.
    – hardillb
    Nov 2, 2017 at 17:07
  • I was looking for something similar to arduino (for example). I don't know where should I start to look at.
    – Lechucico
    Nov 2, 2017 at 17:12
  • Ardunio is not a sensor, it is a micro controller platform that sensors could be attached to. If this is for a large scale deployment in a hospital, you do not want to be building your own sensors, you want an off the shelf part.
    – hardillb
    Nov 2, 2017 at 17:14

2 Answers 2

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You have the options of either using an activity service based on an existing device (i.e. a phone), or reverse engineering an existing device (fitbit or derivative).

This is well established technology, you're likely to find some patented ideas, and some open source code relating to the signal processing.

The actual sensor ought not to be posing a challenge - accelerometers are not new or novel.

Here is a micro:bit stepometer lesson plan, using a cheap board which has all the hardware you need to prototype with. The lesson even has an extension which covers building a commercial product. This hardware is an mcu, BLE, accelerometer and a few LEDs (basically an instance of cujo's answer) but I think it is the lesson plan that you are really looking for.

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  • How I could reverse engineering an existing device? I know that there are a lot of devices, but I need someone that is reliable, efficient and and affordable.
    – Lechucico
    Nov 3, 2017 at 15:15
  • @Sean Houlihane do you have an example of any consumer devices that dump raw data?
    – cujo
    Nov 3, 2017 at 15:19
  • @Lechucico Take your pick - employ a consultant, buy a product off the shelf, or learn how to copy. There is a reason some of us get paid well for our work, not everyone finds it easy. We're trying to teach students where to start, look at the link I gave.
    – Sean Houlihane
    Nov 3, 2017 at 17:13
  • @cujo Android has 'activity' as a service. I don't know the details of what you can access if you write an app.
    – Sean Houlihane
    Nov 3, 2017 at 17:13
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    At that level, I highly doubt it would be raw data, but if OP is looking for processed then it would definitely work.
    – cujo
    Nov 3, 2017 at 17:26
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I would recommend you look at building your own custom device and log locally to it, either in a CSV format or something higher grade with better compressibility such as FIT. Then do file transfers periodically and parse your data either on the device either in the cloud or on the phone. A nRF52 microcontroller that has a built-in BLE/ANT radio and is extremely low power, pair that with an accelerometer and you could have a device that runs off a coin cell for probably a few days depending on your radio usage. You would probably need to design your own PCB so it fits your space limitations.

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  • When you mean nRF52 micro-controller, which one is it? If I search for it on internet, there appears so many nRF52 types
    – Lechucico
    Nov 3, 2017 at 15:13
  • Most of them are just variations in the amount of ram/flash and what soft devices for the radios they support. You will probably need to identify what features you need and select the device yourself.
    – cujo
    Nov 3, 2017 at 15:16
  • I should mention, if you are looking strictly at things like steps or something that is already counted by most fitness trackers, then some of them do give you the processed data files in an open format (i.e. Garmin devices use the fit format)
    – cujo
    Nov 3, 2017 at 15:21
  • Okey, I'll take a look! Furthermore, how can I know what fitness trackers use open format for using on my own application? There are a plenty of these over the internet. Cheers!
    – Lechucico
    Nov 3, 2017 at 15:33
  • Unfortunately I don't which ones use which format, only reason I know Garmin is because I have a watch by them. I would assume fitbit does as well but I cannot say for sure.
    – cujo
    Nov 3, 2017 at 15:37

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