CoreBluetooth and Omron Evolv Blood Pressure Monitor - swift

Question

I have been working on trying to support the Omron Evolv Blood Pressure Monitor (BPM) in my app, via CoreBluetooth. Using the Bluetooth SIG documentation about BPM’s (https://www.bluetooth.com/specifications/specs/ and then BLP and BLS) I could connect with the monitor.
I used the following characteristics:
Blood pressure measurement, 2A35
Blood pressure feature, 2A49
Page 10 in the BLS documentation states that the Blood Pressure Measurement is the property Indicate, which to my knowledge behaves similar to the Notify property.
To clarify some code I call in the delegate methods of CBPeripheralDelegate:
func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {
print("connected!")
bloodPressurePeripheral.discoverServices([bloodPressureService])
}
func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {
guard let services = peripheral.services else { return }
services.forEach { service in
print("discovered service: \(service) \n")
peripheral.discoverCharacteristics(nil, for: service)
}
}
In the didDiscoverCharacteristicsFor function I simply loop through the characteristics and check their property.
if char.properties.contains(.read) {
print("\(char.uuid): properties contains .read")
peripheral.readValue(for: char)
}
if char.properties.contains(.indicate) {
print("\(char.uuid): properties contains .indicate")
peripheral.setNotifyValue(true, for: char)
}
if char.properties.contains(.notify) {
print("\(char.uuid): properties contains .notify")
peripheral.setNotifyValue(false, for: char)
I tried both readValue and setNotifyValue for indicate both I still get the following result:
<CBCharacteristic: 0x2829880c0, UUID = 2A35, properties = 0x20, value = (null), notifying = NO>
2A35: properties contains .indicate
<CBCharacteristic: 0x282988180, UUID = 2A49, properties = 0x2, value = {length = 2, bytes = 0x2700}, notifying = NO>
2A49: properties contains .read
I don't really understand why the value of 2A35 is null. I know there are values because with the Omron application I can get the measurements.
My actual questions is: Has anyone has any experience in connecting with (Omron) BPM's using CoreBluetooth and what am I overlooking?
Thanks for answering!

Answer 1

I have tried connecting Ormon Evolv with Android device.
I will tell you what I have learned from it.
NB:- Ble Devices communicates asynchronously, you have to do one GATT operation (eg, read, write, enable notification, enable indication) at a time. The next operation is to be done only after the previous one is successfully done.
My device had the following services.
DEVICE_INFO_SERVICE with UUID 180a
BATTERY_SERVICE_UUID with UUID 180f
CURRENT_TIME_SERVICE_UUID with UUID 1805
BLOOD_PRESSURE_SERVICE_UUID with UUID 1810
The first GATT operation after a successful connect is gatt.discoverServices() . (the event onServicesDiscoverd is trigged, in android)
If you just need the BP reading without reading status and time stamp, just enable indication for UUID 2A35
val bloodPressureService = gatt?.getService(BLOOD_PRESSURE_SERVICE_UUID)
val bloodPressureChar = bloodPressureService?.getCharacteristic(BLOOD_PRESSURE_CHAR_UUID)
gatt?.setCharacteristicNotification(bloodPressureChar, true)
val bloodDescriptor = bloodPressureChar?.getDescriptor(CCC_DESCRIPTOR_UUID)
bloodDescriptor?.value = BluetoothGattDescriptor.ENABLE_INDICATION_VALUE
gatt?.writeDescriptor(bloodDescriptor)