Temperature sensor example

[sandeepmistry]

Temperature sensor example

[sandeepmistry]

@gbuesing that is a great idea! A pull request would be awesome. I could also try with a DHT sensor later.

I'm not to keen about making BLEPeripheral calls inside the interrupt handler (it could confuse state inside the lib). So, my suggestion would be to set a "read temperature" flag to true in the interrupt handler and check for it in the loop. Something like this:

bool readTemperature = false;

// ...

void timerHandler() {
  readTemperature = true;
}

// ...

void loop() {
  blePeripheral.poll();

  if (readTemperature) {
    setTempCharacteristicValue();
    readTemperature = false;
  }
}

What do you think? Another, improvement would be to start/stop the timer on connect/disconnect or subscribe/unsubscribe.

On a side note, it's a bit weird that the nRF8001 and nRF51822 don't let you know about read requests, so you can return dynamic data - but a timer is perfect for notify characteristics.

[gbuesing]

That makes sense -- just set a flag in the interrupt handler, and do the sensor reading and characteristic setting in loop(). I tested this approach and it seems to work. Created a pull request with this skeleton: #11

Integrating with a DHT is a good idea -- could also expose the humidity as a second service. I'll give this a shot when I get a chance.

Re: starting/stopping timer on connect/disconnect -- if the peripheral spends a lot of its time advertising, that could save work, and maybe battery. But the potential issue I see is: if a client connects and immediately reads the value, they'd see a value from the last connection, which could have occurred a long time ago.

Ultimately would be nice to figure out how to make this run with very little power - though that might be device (e.g. avr/sleep) and use-case dependent.

[gbuesing]

I added code to get real temperature and humidity readings from a DHT22 sensor: https://github.com/gbuesing/arduino-BLEPeripheral/blob/temp_sensor/examples/temp_sensor/temp_sensor.ino

I'm only updating the characteristics when there's a significant change in the reading, which should minimize radio usage for notify events.

Pull request: #11

[sandeepmistry]

Which Arduino board are you using? I've managed to get idle power consumer to < 2mA with the Blend Micro (this is without the DHT22).

[gbuesing]

I'm prototyping on an Uno -- I intend to move the circuit to an Adafruit Pro Trinket 3.3V, or possibly a boarduino.

RedBear has a good example of how to dial system functions down for sleep: http://redbearlab.com/blend-low-power-settings/

But AFAICT the TimerOne library (which I'm using to sample the DHT every two seconds) won't work when in SLEEP_MODE_PWR_DOWN.

I think this could be achieved with the watchdog timer, though?

[sandeepmistry]

I don't have much experience with timers and watchdogs on the Arduino, but once you figure things out a pull request for a low power mode example would be great :)

My <2mA idle power consumption is based on the Blend example.

#11 closes this.

[gbuesing]

Ok will do!