iPhone BLE HRM App connection crashes ORM with "Uncaught Exception: TypeError: Cannot read properties of undefined (reading 'readUInt8')"

[dayreiner]

I installed ORM on a stock 4b with a touchscreen display attached and everything seems to work fine up until attempting to connect BLE heartrate. I'm using an iphone app called HRM Heart Rate Monitor that acts as a BLE go-between for the apple watch and fitness equipment.

As soon as I launch the app on my iPhone, it connects to ORM and I can see the initial heart rate reading as displayed in the app and on my watch, however ORM immediately crashes after this with an Uncaught Exception: TypeError: Cannot read properties of undefined (reading 'readUInt8') error in the log. Not sure if this is a specific compatibility issue with the HRM app's BLE implementation or something else (I do not have a separate BLE HRM to test with), but would be nice to be able to use this if possible since I already have the watch and use it for my other workouts.

Log output below with trace enabled in config.js.

Mar 22 16:34:43 rowingmonitor systemd[1]: Started openrowingmonitor.service - OpenRowingMonitor.
Mar 22 16:34:43 rowingmonitor npm[1321]: > OpenRowingMonitor@0.9.6 start
Mar 22 16:34:43 rowingmonitor npm[1321]: > node app/server.js
Mar 22 16:34:44 rowingmonitor npm[1333]: ==== Open Rowing Monitor 0.9.6 ====
Mar 22 16:34:44 rowingmonitor npm[1333]: ant plus profile: Off
Mar 22 16:34:44 rowingmonitor npm[1333]: SessionManager: Workout plan recieved with 1 interval(s)
Mar 22 16:34:44 rowingmonitor npm[1333]:   Workout parser, recognised justrow interval/split
Mar 22 16:34:44 rowingmonitor npm[1333]: Activating interval settings for interval 1 of 1
Mar 22 16:34:44 rowingmonitor npm[1333]:   Workout parser, recognised justrow interval/split
Mar 22 16:34:44 rowingmonitor npm[1333]: Activating split settings for split 1
Mar 22 16:34:44 rowingmonitor npm[1333]:   Workout parser, recognised justrow interval/split
Mar 22 16:34:44 rowingmonitor npm[1333]: heart rate profile: BLE
Mar 22 16:34:44 rowingmonitor npm[1333]: Opening BLE manager
Mar 22 16:34:44 rowingmonitor npm[1333]: webserver running on port 80
Mar 22 16:34:44 rowingmonitor npm[1333]: Server: peripheral requested refreshPeripheralConfig
Mar 22 16:34:44 rowingmonitor npm[1333]: bluetooth profile: Concept2 PM5
Mar 22 16:34:44 rowingmonitor npm[1333]: Server: peripheral requested refreshPeripheralConfig
Mar 22 16:34:44 rowingmonitor npm[1333]: Found device (HRM App)
Mar 22 16:34:44 rowingmonitor npm[1333]: Connected to 43:2E:E7:A3:16:E2
Mar 22 16:34:45 rowingmonitor npm[1343]: Gpio-service: pin number 17, polling interval 10 us, triggered on Up flank, minimal pulse time 50 us
Mar 22 16:34:45 rowingmonitor npm[1333]: websocket client connected
Mar 22 16:34:45 rowingmonitor npm[1333]: HR device information service was discovered
Mar 22 16:34:46 rowingmonitor npm[1333]: New heart rate value: <Buffer 00 4c>
Mar 22 16:34:46 rowingmonitor npm[1333]: Uncaught Exception: TypeError: Cannot read properties of undefined (reading 'readUInt8')
Mar 22 16:34:46 rowingmonitor npm[1333]:     at GattClientCharacteristic.<anonymous> (file:///opt/openrowingmonitor/app/peripherals/ble/hrm/HrmService.js:222:80)
Mar 22 16:34:46 rowingmonitor npm[1333]:     at cb (/opt/openrowingmonitor/node_modules/ble-host/lib/internal/gatt.js:2206:7)
Mar 22 16:34:46 rowingmonitor npm[1333]:     at /opt/openrowingmonitor/node_modules/ble-host/lib/internal/gatt.js:1781:5
Mar 22 16:34:46 rowingmonitor npm[1333]:     at Object.<anonymous> (/opt/openrowingmonitor/node_modules/ble-host/lib/internal/gatt.js:1027:10)
Mar 22 16:34:46 rowingmonitor npm[1333]:     at AclConnection.<anonymous> (/opt/openrowingmonitor/node_modules/ble-host/lib/ble-manager.js:1703:14)
Mar 22 16:34:46 rowingmonitor npm[1333]:     at AclConnection.emit (node:events:519:28)
Mar 22 16:34:46 rowingmonitor npm[1333]:     at HciSocket.onData (/opt/openrowingmonitor/node_modules/ble-host/lib/internal/adapter.js:1231:16)
Mar 22 16:34:46 rowingmonitor npm[1333]:     at HciSocket.emit (node:events:519:28)
Mar 22 16:34:46 rowingmonitor npm[1333]:     at /opt/openrowingmonitor/node_modules/hci-socket/lib/hci-socket.js:105:9
Mar 22 16:34:46 rowingmonitor npm[1343]: 2026-03-22 16:34:46 sigHandler: Unhandled signal 15, terminating
Mar 22 16:34:46 rowingmonitor npm[1333]: OpenRowingMonitor shutdown at 16:34, at 0.00000 seconds,distance 0.0m
Mar 22 16:34:46 rowingmonitor npm[1333]: RowingData file has not been written, as there was not enough data recorded
Mar 22 16:34:46 rowingmonitor npm[1333]: Garmin fit file has not been written, as there was not enough data recorded
Mar 22 16:34:46 rowingmonitor npm[1333]: Garmin tcx file has not been written, as there was not enough data recorded
Mar 22 16:34:46 rowingmonitor npm[1333]: shutting down all peripherals
Mar 22 16:34:46 rowingmonitor npm[1333]: Shutting down PM5 peripheral
Mar 22 16:34:46 rowingmonitor npm[1333]: Shutting down HRM peripheral
Mar 22 16:34:46 rowingmonitor npm[1333]: Terminating current HRM connection
Mar 22 16:34:46 rowingmonitor npm[1333]: Ble socket is closed
Mar 22 16:34:46 rowingmonitor systemd[1]: openrowingmonitor.service: Main process exited, code=exited, status=1/FAILURE
Mar 22 16:34:46 rowingmonitor systemd[1]: openrowingmonitor.service: Failed with result 'exit-code'.
Mar 22 16:34:46 rowingmonitor systemd[1]: openrowingmonitor.service: Consumed 2.756s CPU time.
Mar 22 16:34:46 rowingmonitor systemd[1]: openrowingmonitor.service: Scheduled restart job, restart counter is at 6.
Mar 22 16:34:46 rowingmonitor systemd[1]: Stopped openrowingmonitor.service - OpenRowingMonitor.
Mar 22 16:34:46 rowingmonitor systemd[1]: openrowingmonitor.service: Consumed 2.756s CPU time.
Mar 22 16:34:46 rowingmonitor systemd[1]: openrowingmonitor.service: Start request repeated too quickly.
Mar 22 16:34:46 rowingmonitor systemd[1]: openrowingmonitor.service: Failed with result 'exit-code'.
Mar 22 16:34:46 rowingmonitor systemd[1]: Failed to start openrowingmonitor.service - OpenRowingMonitor.

[JaapvanEkris]

Hmmm, it works well with Garmin and Polar devices. Perhaps @Abasz has some ideas here?

[dayreiner]

Thanks. Just to add, I also tried a second app called ECHO that provides the same BLE HR functionality, however it also causes the same crash on the ORM side upon connection. So it doesn't seem to be specific to the app I was using but any BLE HR app on the iPhone.

[JaapvanEkris]

Mar 22 16:34:46 rowingmonitor npm[1333]: Uncaught Exception: TypeError: Cannot read properties of undefined (reading 'readUInt8')
Mar 22 16:34:46 rowingmonitor npm[1333]:     at GattClientCharacteristic.<anonymous> (file:///opt/openrowingmonitor/app/peripherals/ble/hrm/HrmService.js:222:80)

Yeah, it crashes on reading the battery level, which appearantly is optional?

[Abasz]

I will have a look. in the meantime can you please try the development branch? there has been changes to the ble stack.

The part thdt is strange is that of there is no battery then there should be no service either and ot should not broadcast anything. My Garmin FR255 does not expose battery and that worked fine.

EDIT:

Actually I am looking at the code the error is that we try to read the battery level and nothing is returned. Obvious solution is to add defensive coding with null check but that might just hide the actual issue. On the other hand this is rather strange that the characteristics is present but it does not return value....

[dayreiner]

I switched to 0.9.7 to no change, however adding in @saschabuehrle's changes to HrmService.js has resolved this issue on my end!

[Abasz]

Can you actually tell me if battery shows up on the dashboard? What I'm trying to check is weather the implementation of the BLE service on the iPhone side is wrong or whether there is any other issue

[dayreiner]

I'm not seeing anywhere on the dashboard where the battery level would be shown, but trace in the logs shows it connecting and sending values.:

Mar 23 12:29:11 rowingmonitor npm[711]: websocket client connected
Mar 23 12:29:48 rowingmonitor npm[711]: Found device (HRM App)
Mar 23 12:29:48 rowingmonitor npm[711]: Connected to 7A:6A:C4:AD:FB:DD
Mar 23 12:29:48 rowingmonitor npm[711]: Disconnected from 7A:6A:C4:AD:FB:DD, restart scanning
Mar 23 12:29:49 rowingmonitor npm[711]: Found device (HRM App)
Mar 23 12:29:49 rowingmonitor npm[711]: Connected to 7A:6A:C4:AD:FB:DD
Mar 23 12:29:49 rowingmonitor npm[711]: Disconnected from 7A:6A:C4:AD:FB:DD, restart scanning
Mar 23 12:29:49 rowingmonitor npm[711]: Found device (HRM App)
Mar 23 12:29:49 rowingmonitor npm[711]: Connected to 7A:6A:C4:AD:FB:DD
Mar 23 12:29:50 rowingmonitor npm[711]: HR device information service was discovered
Mar 23 12:30:03 rowingmonitor npm[711]: New heart rate value: <Buffer 00 46>
Mar 23 12:30:03 rowingmonitor npm[711]: New heart rate value: <Buffer 00 46>
Mar 23 12:30:03 rowingmonitor npm[711]: New heart rate value: <Buffer 00 46>
Mar 23 12:30:03 rowingmonitor npm[711]: New heart rate value: <Buffer 00 46>
Mar 23 12:30:03 rowingmonitor npm[711]: New heart rate value: <Buffer 00 46>