Lite-On Ambient Light & Proximity Sensors

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LTR-501 on a breadboard from Olimex

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LTR-501 Sensor in Home Assistant UI.

The ltr501 sensor platform allows you to use a range of LiteOn ambient light and proximity sensors with ESPHome.

The supported family of sensors includes:

  • Ambient Light Sensor LTR-301ALS

  • Integrated Ambient Light and Proximity Sensors LTR-501ALS and LTR-558ALS

The LTR-501 device is available on a breakout board from Olimex.

The sensors are very similar and share the same datasheet. The I²C Bus is required to be set up in your configuration for this sensor to work. I²C address is 0x23.

Proximity sensors are the same sort of sensors that you find in phones and tablets to disable the screen when you hold the device up to your ear. They might be useful for automated turning on or off of displays and control panels.

Ambient light sensing

These sensors have a linear response over a wide dynamic range from 0.01 lux to 64k lux and are well suited to applications under high ambient brightness. There are two gain settings (1X, 150X) available for use. Use higher gain for dimmer areas.

These devices consist of two photodiodes: a CH0 diode that is sensitive to both visible and infrared light and a CH1 diode that is sensitive only to infrared light.

Note: These sensors do not have internal data checking and do not indicate any errors if data is not reliable. The sensors can be easily saturated if the gain is too high or the integration time is too long. In this case, readings can be very strange. It’s recommended to use automatic mode with a starting gain of 1X (default) and a starting integration time of 100ms (default) or even 50ms (if the sensor is in a very bright environment). Automatic mode with starting gain of 150X is not recommended; use it only if you are sure brightness will never exceed 200-300 lx.

Ambient light illuminance calculation

Excerpt from the datasheet:

RATIO = CH1/(CH0+CH1)
IF (RATIO < 0.45)
    ALS_LUX = (1.7743 * CH0 + 1.1059 * CH1) / ALS_GAIN / ALS_INT
ELSEIF (RATIO < 0.64 && RATIO >= 0.45)
    ALS_LUX = (3.7725 * CH0 – 1.3363 * CH1) / ALS_GAIN / ALS_INT
ELSEIF (RATIO < 0.85 && RATIO >= 0.64)
    ALS_LUX = (1.6903 * CH0 - 0.1693 * CH1) / ALS_GAIN / ALS_INT
ELSE
    ALS_LUX = 0
END

where:

  • CH0 and CH1 are the sensor values (measurement counts) for Visible + IR (Ch0) and IR only (Ch1) sensors respectively.

  • ALS_GAIN is the gain multiplier

  • ALS_INT is the integration time in ms/100

ALS Gain levels

The table lists gain values and corresponding illuminance range:

Gain

Illuminance range

1X

2 lux to 64k lux (default)

150X

0.01 lux to 320 lux

This Wikipedia article has a table of some lux values for comparison.

The following table lists possible gain and integration time combinations:

Gain / Int.time

50 ms

100 ms

200 ms

400 ms

1X

✓

✓ (default)

150X

✓

✓

✓

Proximity sensing

The proximity sensor has a built-in emitter and detector. The sensor detects reflected IR light from the emitter and gives a raw count value inversely proportional to the distance squared. A decrease in the count value means an object is getting further away from the sensor (and vice-versa). Neither of the datasheets provide any information on how to convert the raw count value to distance. The only way to do so is to test the sensor yourself and select the threshold according to your needs and environment. Exact values will depend on the type of the object, its color and reflectivity.

Example configuration

sensor:
  - platform: ltr501
    type: ALS_PS  # .. or ALS or PS
    ambient_light: "Ambient light"
    # PS only section
    ps_cooldown: 5 s
    ps_high_threshold: 500
    on_ps_high_threshold:
      then:
        - .... # do something - light up the screen for example
    ps_counts:
      name: "Proximity counts"

Configuration variables

  • id (Optional, ID): Manually specify the ID used for code generation.

  • address (Optional, int): Manually specify the I²C address of the sensor. Default is 0x23.

  • type (Optional, string): The type of the sensor. Valid values are ALS_PS (default) for integrated sensors, ALS for ambient light only or PS for proximity only devices.

  • auto_mode (Optional, boolean): Automatic gain and integration time selection. Defaults to True.

  • gain (Optional, string): The gain the device will use. Higher values are better in low-light conditions. Valid values are 1X (default), 150X.

  • integration_time (Optional, Time): The amount of time sensors are exposed. Longer means more accurate values. Valid values are: 50ms, 100ms (default), 200ms, 400ms.

  • glass_attenuation_factor (Optional, float): The attenuation factor of glass if it’s behind some glass or plastic facia. Default is 1.0 means 100% transmissivity. 2 means 50% transmissivity etc.

  • update_interval (Optional, Time): The interval for checking the sensors. Defaults to 60s.

  • ps_cooldown (Optional, Time): The “cooldown” period after the proximity sensor is triggered. Helps to avoid multiple calls. Defaults to 5s.

  • ps_gain (Optional, string): The gain the device will use for proximity sensor. Higher values are better in low-light conditions. Valid values are 1X (default), 4X, 8X, 16X.

  • ps_high_threshold (Optional, int): The threshold for the proximity sensor to trigger on object getting closer. Defaults to 65535, which implies it will never be triggered.

  • ps_low_threshold (Optional, int): The threshold for the proximity sensor to trigger on object getting further away. Defaults to 0, which implies it will never be triggered.

  • on_ps_high_threshold (Optional): Actions to perform when the proximity sensor is triggered on object getting closer.

  • on_ps_low_threshold (Optional): Actions to perform when the proximity sensor is triggered on object getting further away.

Sensors

This component offers five sensors for ALS-equipped devices and one sensor for PS-equipped devices. You can configure all or any subset of these sensors. Each configured sensor is reported separately on each update_interval. Each is an ESPHome sensor and may be configured accordingly; if you don’t need to configure additional sensor variables, you may simply use the shorthand syntax for the sensor. For example: ambient_light: "Ambient light"

  • ambient_light (Optional): Illuminance of ambient light, close to human eye spectre, lx.

  • infrared_counts (Optional): Sensor counts from the IR-sensitive sensor (CH1), counts.

  • full_spectrum_counts (Optional): Sensor counts from the sensor sensitive to both visible light and IR (CH0), counts.

  • actual_gain (Optional): Gain value used to measure data, multiplier. Particularly useful when “auto_mode” is selected.

  • actual_integration_time (Optional): Integration time used to measure data, ms. Particularly useful when “auto_mode” is selected.

  • ps_counts (Optional) - Raw 11-bit reading from proximity sensor, counts.

See Also