[MUSIC PLAYING]

Welcome to the TI Precision Lab series on light sensing. My name is Rahland Gordon, and I am an applications engineer for Texas Instruments optical sensors. This video will discuss the use of light sensors for temperature detection applications.

Many systems require a method to detect tampering, and the use of a light sensor is an effective and simple solution. That could mean detecting that the door of a product has been opened, that a seal on a device has been breached, or that any external element is affecting the measurement precision. Device tampering can have many negative impacts, including unexpected changes in functionality, a safety risk to humans, security breaches, or ruin devices.

The use for tamper detection is appropriate when there is a safety critical need to shut off a portion of a product if opened, such as a smart lock or high voltage power supply. A possibility that a device will be damaged once tampered with, such as products submerged in water or other harsh conditions, or the potential that a user may tamper with the device to alter its functionality, such as an electricity meter.

A light sensor can determine a change in illumination and can sense and increase optical response during a broken seal or open case scenario. For design with a known amount of light at the PCB, a light sensor offers an easy way to implement tamper detection.

Once the light level rises, the end equipment has entered an unexpected state, thus indicating that your end equipment has been tampered with. There are several advantages of using a light sensor for temperature detection applications, such as simple design complexity, low power consumption, and a low cost solution.

For a more secure tamper detection, it is useful to be able to sense a broad spectrum of light, including both visible and infrared wavelengths. Infrared light can be used to see more clearly in low lighting conditions without the use of visible light. Light sensors such as the OPT 3002 have a wide optical spectrum from 300 nanometers to 1,000 nanometers, which includes some ultraviolet, visible, and infrared wavelengths, enabling the detection of more light sources.

To increase the effectiveness when using a light sensor for tamper detection, it is important to consider the light sensor measurement levels across a broad spectrum of wavelengths. The optical power, or irradiance, typically measured in watts per meter squared, measures the light intensity across all wavelengths. This is slightly different from illuminance, which was discussed in chapter 1, as illuminance is a photometric measurement.

Being able to detect low amounts of optical power ensures that, even with a slight opening for light to come in, the sensor can detect that the end equipment has been tampered with. With TI's OPT 3002, the measurement level is as low as 1.2 nanowatts per centimeter squared, which enables the detection of very small amounts of light.

In some applications that are battery powered, the expectation is that they last for long periods of time. In these cases, the use of a light sensor with very low power draw will minimize the effect of the sensor on the overall system power draw.

Another important consideration in low power applications is how often the microprocessor needs to read from the sensor. In light sensors without an interrupt functionality, the microprocessor must continually read the sensor and compare it to the threshold. Some light sensors, such as TI light sensors, support integrated comparisons with programmable thresholds, different types of interrupt modes, and support for interrupt pin.

These features allow the end equipment to take advantage of a single digital signal that indicates whether the light is above or below the levels of interest, and they also allow the microprocessor to sleep and only wake up to take action when the light level crosses the threshold, greatly reducing the MCU active time.

For more light censor technical resources, and to search TI products, please visit the link shown. Thanks for taking the time to watch this video. Please try the following quiz.

Why might you want to use a light sensor with the interrupt feature for tamper detection? This feature allows a microprocessor to sleep and only wake up to take action when a light level crosses a threshold set, thus saving power. Also, this feature allows you to take advantage of a single digital signal that indicates whether the light is above or below the levels of interest.