# SCD4X

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Use [Sensirion SCD4X](https://www.sensirion.com/en/environmental-sensors/carbon-dioxide-sensors/carbon-dioxide-sensor-scd4x) [CO2](https://en.wikipedia.org/wiki/Carbon_dioxide) sensors (SCD40 and SCD41) in Elixir.

## Usage

### Start the sensor server

```elixir
iex> {:ok, scd} = SCD4X.start_link(bus_name: "i2c-1")
{:ok, #PID<0.1407.0>}
```

### Periodic measurement

The sensor updates the measurement every 5 seconds once the periodic measurement is started.

```elixir
iex> SCD4X.start_periodic_measurement(scd)
:ok

iex> SCD4X.measure(scd)
{:ok,
 %SCD4X.Measurement{
   co2_ppm: 612,
   humidity_rh: 59.07440185546875,
   temperature_c: 30.331497192382812,
   timestamp_ms: 620482
 }}

SCD4X.stop_periodic_measurement(scd)
:ok
```

### Single shot measurement

The measurement can be performed on demand without the periodic measurement.

```elixir
iex> SCD4X.measure(scd, :single_shot)
{:ok,
 %SCD4X.Measurement{
   co2_ppm: 638,
   humidity_rh: 70.49713134765625,
   temperature_c: 26.63848876953125,
   timestamp_ms: 400768
 }}
```