Some sensors are able to generate an interupt when a certain metric value is exceeded. When enabled, you will receive an update of the metric value if the threshold is exceeded.

We allow to define two thresholds, i.e., threshold low and threshold high. When a metric value exceeds the threshold high (TH) an interrupt is generated. In contrast, only when a metric value goes below threshold low (TL) an interrupt occurs. This allow us to get updates in three distinct manners.

In all cases an interrupt is generated when the metric value exceeds TH or when is falls below TL. When playing with the TH and TL configuration we can manipulate when we want an update.

1. If we are interested to be notified when a value is higher than TH or lower than TL, we define: TH with a higher value as TL. For example: if we want to get sensor data when a sound level exceeds 100 dB or when it is lower dan 80 dB, we set TH=100 and TL=80.

2. If we are interested when a value enters the area between TH and TL, TL has a higher value than TH. For example: if we want to get sensor data when a sound level is between 80 and 100 dB, we set TH=80 and TL=100.

3. If we want to know when a metric value crosses a specific value, we can define TH equal to TL. For example: if we want to get sensor data when a sound level crosses 85 dB, regardless if the sound level was higher or lower before, we set TH=85 and TL=85.

In the figure below, dashed horizontal lines indicate when sensor data is transmitted to the gateway.

In the table below you can find the minimum and maximum values TL and TH can take, for each physical quantity and each sensor.

Pay attention! Due to the manner in which sound levels are calculated, the measured sound level is always at least 70 dB. Therefore it does not make sense to try to measure ‘quiet’ sounds. It is also not allowed to set thresholds lower than 75 dB, as this will lead to constant data transmission, which consume a lot of power and will drain the battery.

---