TI CC2650STK SimpleLink™ IoT SensorTag - Review

Table of contents

RoadTest: TI CC2650STK SimpleLink™ IoT SensorTag

Author: jbaczuk

Creation date: 28 Jun 2015

Evaluation Type: Independent Products

Did you receive all parts the manufacturer stated would be included in the package?: True

What other parts do you consider comparable to this product?: Analog devices ADXL345, Freescale MMA8451, Dialog DA14580.

What were the biggest problems encountered?: The rubber case doesn't quite hold the plastic box in well, and fell out a few times when pulling from the pocket. I assumed it was meant for a keychain based on the rubber casing design, but it doesn't really hold the plastic enclosure well during transitions in and out of the pocket. It should probably encase the plastic better to prevent slippage. How do you access the microphone from the app? In the motion data section, which color (b,r,g) is x,y, and z? Consider matching the text colors to the chart line colors. Schematic says "Gyroscope and Accelerometer ", should also say "Magnetometer" for clarity. The magnet sensor says "Reed Relay" in the schematic, so it took me a while to figure out it was the magnet sensor. Link to the MPU-9250 website and datasheet are both broken.

Detailed Review:

1. First Impressions
   1. Unboxing was fun!  It wasn't a typical dev kit, you know, the typical circuit board with a bunch of headers in an anti-static bag.  The SensorTag, however, is a nicely packaged circuit board with a battery inside a plastic enclosure, and a rubber keychain casing.  It was nice to see that there were also indicators on a clear plastic window that show where the sensors might be, as well as buttons on the side.  Nice design aesthetics.
   2. A general use case is a bit unknown.  You can't argue that this kit has everything.  There are more sensors than you could ever need in a single application, and it supports the latest 2.4GHz wireless protocols standard (except WiFi).  TI is taking a stab at capturing some market share in the IoT with their sensors by creating a hardware platform for designers, including mobile and web applications, which they've done a great job with.  They used all TI sensors where they could, and surprisingly, half the sensors were added from other vendors where TI doesn't have a market.  These software components provide a basic API for running any type of application on virtually any internet-connected hardware, so they seem to have captured the idea of IoT.
      
2. Setup
   1. Setup was amazingly simple.  I didn't realize that there was also a power button when you pull the tab on the battery because that wasn't mentioned in the getting started guide.  It isn't typical to have to press a power button on a dev kit, especially bluetooth-based kits that use a coin cell battery.  I assumed it would power on when the tab was pulled.
   2. The mobile app is awesome!  I like how it graphs the data every second and can upload data to the cloud.  The web interface is also very slick.  I was blown away at the work that went into the mobile app and web stack.
3. Hardware Design
   1. Ambient temperature sensor (TMP007): This sensor is impressive, it is a fully functional infrared sensor with a built-in local temperature sensor.  It also does the temperature calculation with a built-in Math engine.  Placement is not ideal, because it is covered by a plastic mesh which doesn't look like it was specifically designed as an optic channel, and it reflects and refracts some of the IR, which slightly affects the readings (average drop of 2-3deg C compared to without the clear plastic cover).
   2. Ambient light sensor (OPT3001):  This sensor claims to have a very tight wavelength response that matches the human eye.  This could be good for adjusting light levels in a room automatically, for example.  Also placement is ok, it does have a clear view to the outside, but the plastic cover does reflect some of the light and measurements are 5-10lux lower with the case on.
   3. Humidity sensor (HDC1000): This sensor has 14 bit measurement resolution with a range of 0% to 100%.  It also has a built in temperature sensor so there is some redundancy in features, though it probably isn't being used.  Seems like a decent humidity sensor at first glance.
   4. Pressure sensor (BMP280): This Bosch sensor ranges from 300 to 1100hPa which is -500m to +9000m (sea level), everest is at 8,848m so it has plenty range.  The resolution, however is only 1m at room temperature, and can increase up to 10m at other temperatures.  This isn't super great, but probably good for a basic pressure sensor.  The enclosure has only the hole array as openings to the air (when the rubber case is on), but it is probably sufficient.
   5. Motion tracking device (MPU-9250): This sensor is a 9-axis motion device meaning it can do 3 axes on each of the sensors (accelerometer, gyro, and magnetometer).  This is perfect for sensor fusion where you might want to track the exact movement of the device including orientation.  This can be used as a control device just like a Wii remote.  The chip has 2 separate silicon die in a single package (a separate die for the magnetometer), even so the package is only 3mmx3mm, which is pretty good.  It has built in motion processing.  Resolution is up to 16-bit on all 3 ADC's, which is great.
   6. Magnet sensor (MK24): This is a very simple on/off magnet reed switch.  The distance is about 2-3cm using a 2-3cm dia. neodymium magnet, which seems pretty low as any smaller magnets reduce the range significantly.  The magnet also affects the magnetometer significantly so you can't expect to get readings from that and the reed switch at the same time.
   7. Antenna: The kit uses a trace antenna which takes up nearly 1/3 of the board, and has a coaxial connector for an external antenna.  A chip antenna would not take as much space, although ground plane would still be required.
4. Firmware
   1. The sample rate is 1Hz out of the box.  I think with many IoT devices, especially in large quantities, a server setup would be significantly affected by the volume of data.  In wearable and critical applications, the sensors may need to be sampled more often than every second, and this may be a problem depending on the server setup and internet speed.  It would be nice to be able to change the sample rate as part of the custom bluetooth GATT profile.
5. Software
   1. The mobile app is quite impressive.  There is a few things that could be fixed like labeling the colors of the axes on the 9-axis sensor, for example.  The web app looks similar to the mobile app, but not a super pretty interface.  However, it all works great out of the box, and they have done a very good job of getting it all IoT ready.  There is even an api you can use to query the sensor from other applications.
6. Summary
   1. The sensor kit is a great piece of hardware, with great supporting software to set up a almost any type of sensor to the cloud.  For $29 it is not a bad price to pay to get all of these features.  It isn't super portable, as the board is pretty large, mostly due to the large CR2032 battery and the trace antenna.  The battery could be switched for a smaller coin cell battery or a rechargeable pack to become more portable, but then you'd get either less power, or have to add recharging circuitry.  If you want to program custom firmware, you would probably want to purchase a dev kit for $15, although it can do OAD (over the air downloads).  They've captured the sensing part of IoT with this great H/W and S/W kit, highly recommended.