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sensors External Sensors

Overview

As already mentioned in the Logged Data Section GPSLogger supports some additional external sensors. Mainly this feature has been added for my own cycling & running activities, so please understand that there might be a limitation when it comes to support of specific sensor brands or types.

The implementation is based 1:1 on the Protocol specifications (either ANT+ or BluetoothLowEnergy/Bluetooth) - so if your sensor is supporting the standard implementation of the protocol, it should work 🤞 (I’ll keep my fingers crossed).

Once you have paired a Sensor with GPSLogger, the app will always (try to) connect to the sensor during the startup. So it’s pair once - use forever. Of course, you can remove previously paired sensors vie the application settings. You also have the possibility to select from the list of paired sensors which you actually want to use (this especially applies to multi profiles).

You can make use of the audio announcement feature in order to get feedback about the connection state of each of your sensors. Additionally, you can enable the display of connection status information via the Application Settings.

BluetoothLowEnergy / Bluetooth

In the year 2022 we mainly talk about BluetoothLowEnergy (als known as BluetoothLE, BTLE or just BLE) Sensors. The probability that you buy a Bluetooth Sensor is IMHO quite low. But be aware that a lot of old fitness equipment still uses the old 5.3Khz Bluetooth (and not BTLE) technology. This kind of hardware can’t be used with GPSLogger.

So if you see the sign printed on your sensor - but it does not work with GPSLogger, then the chance is quite high that this is an old device. You might like to double-check with an app like nRF Connect for Mobile from Nordic Semiconductor if your sensor is visible by any way. If nRF Connect does not list/show your sensor, GPSLogger isn’t able to use it either.

If nRF Connect shows your sensor in the list, but GPSLogger is not able to connect to it - please get in contact with me - TIA!

Heartrate

Make sure your sensor is supporting the transfer of pulse data as described in the Bluetooth Heartrate Service Specification. There exists some old chest straps that make use of an old/deprecated Bluetooth standard which is quite energy consuming. Please note, that it’s not possible to use such an old-5.3Khz-technology-sensor with GPSLogger.

The Heartrate Service exposes heart rate and other data related to a heart rate sensor intended for fitness applications.

  • Heart Rate Measurement
    • Heart Rate Measurement Value - Unit: beats per minute (bpm)
    • Sensor Contact Status
    • Energy Expended - Unit: kilo Joules
    • RR-Interval (The RR-Interval value represents the time between two R-Wave detections)

  • Body Sensor Location: Other, Chest, Wrist, Finger, Hand, Ear Lobe or Foot

  • Heart Rate Control Point: Resets the value of the Energy Expended field in the Heart Rate Measurement characteristic to 0

I myself use quite a cheap chest strap from Genonaute (from Decathlon)1 - but can also confirm that the Dual Sensors from Polar, Garmin or Wahoo will work. And thanks to Holger we also solved an issue with the G.PULSE 3 in 1.

Cadence / (Speed &) Cadence

The Cycling Speed and Cadence (CSC) Service exposes speed-related data and/or cadence-related data while using the Cycling Speed and Cadence sensor (Server). The Service provides:

  • The CSC Measurement characteristic (CSC refers to Cycling Speed and Cadence) is a variable length structure containing a Flags field and, based on the contents of the Flags field, may contain one or more additional fields:
    • Cumulative Wheel Revolutions - Unit less
    • Last Wheel Event Time - Unit has a resolution of 1/1024s
    • Cumulative Crank Revolutions - Unit less
    • Last Crank Event Time - Unit has a resolution of 1/1024s

  • Sensor Location: Other, Top of shoe, In shoe, Hip, Front Wheel, Left Crank, Right Crank, Left Pedal, Right Pedal, Front Hub, Rear Dropout, Chainstay, Rear Wheel, Rear Hub, Chest, Spider or Chain Ring

  • SC Control Point see Bluetooth Specification sc_control_point.xml for details

  • The CSC Feature characteristics:
    • Wheel Revolution Data Supported (Y/N)
    • Crank Revolution Data Supported (Y/N)
    • Multiple Sensor Locations Supported (Y/N)

If you have a single Cadence sensor, then only the Cumulative Crank Revolutions and the Last Crank Event Time will be present in a CSC Measurement - anyhow the app will ignore any additional speed data (since the value will be taken based on your GPS).

I use multiple CAD-Sensors on different bikes: the one from Garmin, the old magnet-based one from BTWIN (a Decathlon brand) and the CAD-Sensor from Wahoo (which I can’t recommend since it hasn’t provided any values below 20 rpm during my testings)1

Cycling Power-meter

The Cycling Power (CP) Service exposes power- and force-related data and optionally, speed- and cadence-related data from a Cycling Power sensor intended for sports and fitness applications. The Service provides:

  • The Cycling Power Measurement characteristic is a variable length structure containing a Flags field, an Instantaneous Power field and, based on the contents of the Flags field, may contain one or more additional fields:
    • Instantaneous Power - Unit is in watts
    • Pedal Power Balance - Unit is in percentage with a resolution of 1/2
    • Accumulated Torque - Unit is in newton metres with a resolution of 1/32
    • Cumulative Wheel Revolutions - Unit less
    • Last Wheel Event Time - Unit is in seconds with a resolution of 1/2048s
    • Cumulative Crank Revolutions - Unit less
    • Last Crank Event Time - Unit is in seconds with a resolution of 1/1024s
    • Maximum Force Magnitude - Unit is in newtons
    • Minimum Force Magnitude - Unit is in newtons
    • Maximum Torque Magnitude - Unit is in newton metres with a resolution of 1/32
    • Minimum Torque Magnitude - Unit is in newton metres with a resolution of 1/32
    • Maximum Angle - Unit is in degrees
    • Minimum Angle - Unit is in degrees
    • Top Dead Spot Angle - Unit is in degree
    • Bottom Dead Spot Angle - Unit is in degrees
    • Accumulated Energy - Unit is in kilojoules

  • The Cycling Power Vector
    • Cumulative Crank Revolutions - Unit less
    • Last Crank Event Time - Unit is in seconds with a resolution of 1/1024s.
    • First Crank Measurement Angle - Unit is in degrees
    • Instantaneous Force Magnitude Array - Unit is in newtons
    • Instantaneous Torque Magnitude Array - Unit is in newton/meters with a resolution of 1/32

  • Sensor Location: Other, Top of shoe, In shoe, Hip, Front Wheel, Left Crank, Right Crank, Left Pedal, Right Pedal, Front Hub, Rear Dropout, Chainstay, Rear Wheel, Rear Hub, Chest, Spider or Chain Ring

  • The Cycling Power Control Point see Bluetooth Specification cycling_power_control_point.xml for details

  • The Cycling Power Feature characteristic:
    • Pedal Power Balance Supported (Y/N)
    • Accumulated Torque Supported (Y/N)
    • Wheel Revolution Data Supported (Y/N)
    • Crank Revolution Data Supported (Y/N)
    • Extreme Magnitudes Supported (Y/N)
    • Extreme Angles Supported (Y/N)
    • Top and Bottom Dead Spot Angles Supported (Y/N)
    • Accumulated Energy Supported (Y/N)
    • Offset Compensation Indicator Supported (Y/N)
    • Offset Compensation Supported (Y/N)
    • Cycling Power Measurement Characteristic Content Masking Supported (Y/N)
    • Multiple Sensor Locations Supported (Y/N)
    • Crank Length Adjustment Supported (Y/N)
    • Chain Length Adjustment Supported (Y/N)
    • Chain Weight Adjustment Supported (Y/N)
    • Span Length Adjustment Supported (Y/N)
    • Sensor Measurement Context (Y/N)
    • Instantaneous Measurement Direction Supported (Y/N)
    • Factory Calibration Date Supported (Y/N)
    • Enhanced Offset Compensation Supported (Y/N)
    • Distribute System Support [Unspecified (legacy sensor), Not for use in a distributed system, Can be used in a distributed system, RFU]

Again my personal setup - I use the Assioma Duo from Favero Electronics1

FTMS Treadmill Service providing Treadmill Data

The data available from the various characteristics will be used to a) simulate your current location and b) control your treadmill speed and incline. see Treadmill Section of this manual

rowing FTMS Rowing-Machine providing Rowing-Machine Data

see Rowing-Machine Section of this manual

Additional non-standard BluetoothLE Sensors/Devices supported by GPSLogger

ANT+

The ANT+ protocol is under the control of GARMIN and is the standard in the cycling world. Since a couple of years ago the required hardware to be able to receive data from an ANT+ sensor is not built any longer into smartphones. Apple started withdrawing the support if I remember correctly with the iPhone 6 (if not earlier) and other hardware manufactures have followed the Apple route.

IMHO ANT+ has reached a dead end for smartphones.

Before you are able to connect any ANT+Sensor with GPSLogger you need:

  • Android Device with build-in ANT+ hardware
  • The manufacture of the device has to compile valid ANT+ drivers into its Android OS (for my last phone with build-in ANT+ hardware the manufacture has withdrawn ANT+ support on hardware driver level with its latest OS update)

Additionally you need to install:

Just another side note: When I used ANT+ on my phone I ran into serious Wi-Fi-connection issues while my phone was on roaming (on vacation) and trying to connect to my ANT+ HR Sensor (each time Wi-Fi was turned off). So I have my opinion about the quality concerning the ANT+ drivers (built in Canada) but make your own experience.

Supported ANT+ Sensors

  • Heartrate Sensors
  • Cadence / Speed & Cadence Sensors

  1. Please note this is NOT AN ADVERTISEMENT I just use/own these devices - and I paid the regular price. ↩ ↩2 ↩3

Version: 2023/03/19