Scheduling a Digital Temperature Sensor One Shot Conversion

A successful bus read immediately after a one shot command does not necessarily return a new temperature measurement. The result register may still contain an earlier conversion or a startup value. Build the schedule around the device’s conversion sequence and averaging configuration rather than the time needed to transfer bytes.

Identify all timing intervals

The TI TMP117 data sheet distinguishes power up time, individual conversions, averaging, and conversion cycle behavior. Averaging is available in one shot operation and increases the time before the final reported result is ready.

Record the power state, averaging setting, command acceptance point, maximum conversion duration, and result availability behavior. Avoid substituting a typical conversion time for a required upper bound when scheduling an unattended read.

Track result freshness explicitly

Associate each requested conversion with its command time and completion evidence. Use the supported data ready or timing method, including the documented effects of reading status registers. A flag that clears on read needs a different polling strategy from a persistent status bit.

Do not infer freshness because the numerical temperature changed. A stable environment can produce identical valid readings, while an old value can differ from a software variable that was reset during startup.

Include averaging in the energy budget

Averaging multiple conversions can reduce output variation but keeps the measurement circuitry active longer. Calculate active time from the configured number of conversions and the applicable device timing, then add the idle interval and communication overhead.

For a hypothetical sensor that takes 20 ms per conversion, averaging eight conversions occupies about 160 ms before additional overhead. Polling every 50 ms does not make that averaged result arrive sooner and may repeatedly retrieve the same data.

Verify the complete wake sequence

Capture supply, command traffic, and the completion indication during a cold start, an ordinary wake, and a rapid repeated request. Confirm that configuration writes occur after the device can accept them and that a new request does not unintentionally replace an unfinished measurement.

Test bus errors and timeout handling with a bounded recovery path. Report an unavailable or stale sample as such rather than substituting a startup code into the temperature history.

Save the timing diagram, configuration values, maximum wait, and freshness rules. Keep electrical conversion latency separate from the sensor’s thermal response to the object being measured. A conversion can be digitally complete while the package is still approaching thermal equilibrium. A reliable one shot implementation establishes both when the result is new and what physical temperature condition that result can represent.