C++ Tinyb ble temperature reader application gives constant readings which doesn't reflect the actual temperature variation

ba_kirang · 05-27-2019, 01:37 AM

I am trying to read temperature values from a BLE Temperature sensor (bluemaestro tempo disc)

I am developing in c++ using intel's tinyb library which requires bluez.

Relevant code snippet:

Code:

using Iter = std::vector<std::unique_ptr<tinyb::BluetoothDevice>>::const_iterator;
while (true)
{
    for (Iter it = sensor_tag_array.begin(); it != sensor_tag_array.end(); ++it)
    {
        std::string address_ = (*it)->get_address();

        std::map<uint16_t, std::vector<uint8_t>> mfg__ = (*it)->get_manufacturer_data();
        for (auto it : mfg__)
        {
            if (it.second.empty())
                logger_->error("{}, {} :Empty mfg for : {}", __FILENAME__, __func__, bleMap[address_].sensor_name);
            else
            {
                if (it.second.front() == 23)
                {
                    battery_lvl = it.second[1];
                    first_byte = it.second[6];
                    second_byte = it.second[7];
                    temperature = convert_to_actual(first_byte, second_byte) / 10.0;
                    std::cout << "\nTemperature is for : " << bleMap[address_].sensor_name << " : " << temperature << "\n";
                }
            }
        }
}

This was properly giving the correct relatime values until now. But suddenly it started printing a single constant reading each time the application is restarted. Whatever temperature value is first read at application startup is repeated throughout the application runtime. I used the tempo utility app to verify that the sensor is actually reporting the correct realtime values.

I tried re-installing the OS (Ubuntu 18.04.1), tried multple version of bluez ( 5.48 which is pre-installed,5.39 and 5.37) but the issue is still there.

I also changed the advertisement frequency in the bluemaestro device.

How to resolve this ?

astrogeek · 05-27-2019, 03:33 PM

Quote:

Originally Posted by ba_kirang

This was properly giving the correct relatime values until now. But suddenly it started printing a single constant reading each time the application is restarted. Whatever temperature value is first read at application startup is repeated throughout the application runtime. I used the tempo utility app to verify that the sensor is actually reporting the correct realtime values.

Then the obvious question to ask is what changed between when it worked, and when it no longer worked.

Did you make a change to your application code, intentionally or otherwise? Something obviously changed and it is possible but unlikely to be due to the operating system.

Review your code carefully and verify that each variable and your loop parameters are what you think they are at each point. Use a few printfs or couts to see the values at each point, and/or use gdb to trace the internal state if necessary.

Set up a minimal test case which demonstrates the unexpected behavior and verify that you have correctly polled the sensor according to its documentation, and that you correctly handle the resulting data array it returns.