Change the HeartRateSensor frequency

[PatTheDog]

I have a clockface that reads the heart rate bpm every 8 seconds and stores it in an array so I can draw a graph of the my heart rate for the past 10 minutes.

I initiate the sensor with const hrm = new HeartRateSensor({ frequency: 8 });

In addition to populating the array every 8 seconds, I would like to read the hrm.heartRate in order to populate a text field. But I would like to do this every second.

So my question is, how can I make the frequency of hrm 8 when the display is off, and change it to 1 when the display is on? Is it simply a case of hrm.frequency = 1?

[JonFitbit]

You can use setOptions()

https://dev.fitbit.com/blog/2019-10-29-announcing-fitbit-os-sdk-4.0/#sensor-apis

[PatTheDog]

Thanks @JonFitbit  Interestingly, although I initiate the sensor with frequency: 8, I'm still able to get varying heartRate values far more frequently than 8 seconds, for example if I read them on the clock tick. Likewise, if I use the code below, I'll get an almost continuous stream of values

hrm.addEventListener("reading", () => {
    console.log(`Current heart rate: ${hrm.heartRate}`);
  });

Could you please clarify what the frequency option is actually doing?

[PatTheDog]

Ah, I think I see my misunderstanding. Frequency is not seconds between readings, it's the number of readings per second (hz)! 

[Gondwana]

I know you're not talking to me, but I think the answer is that the frequency just sets how often your event handler (callback) function is called. You'll probably find that readings only change every three seconds or so, at best.

[PatTheDog]

Yes, thanks Gondwana. I realised my error just after posting. Of course, the clue is in the word "frequency"!