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Hello, there. From the low power amplifiers and comparators group at TI, we present this short video on PIR motion detectors. We will analyze the overall motion detecting system while paying close attention to the surrounding analog components making up the signal chain. As we step through the system, we'll highlight the need for low power devices and also the key differences between analog and digital PIR solutions.

PIR motion detectors are commonly used in industrial and building automation systems in applications like video surveillance or lighting networks. Think about automatic lights in large buildings or your thermostat that lights up as you walk by for everyday examples. In this image, we see an example of a dual detector that combines two sensors to provide a wider detection angle as indicated by the blue and red dotted lines. Many real life systems utilize a dual detector setup like shown, but for our video, we'll stick to analyzing a single detector circuit for simplicity.

TI has a large portfolio of nanopower devices that are well-suited for low power PIR systems and makes it easy to find everything in one place. We'll highlight some key devices as you step through our system. To start, let's look at the overall PIR signal chain.

Here are the four main blocks that make up a PIR motion sensing system. First, we start with the PIR sensor, which outputs a waveform depending on the IR energy it detects. Stage two, perform signal conditioning to prepare the input for detection, and stage three is often an ADC that compares the cleaned up signal to an adjustable internal threshold. If the signal exceeds the threshold, it wakes up the microcontroller and lets the system know that something is detected. It's important to note that the ADC can be discrete, as shown here, or integrated into the microcontroller.

We'll focus on the first three blocks in this video, which you'll notice are all labeled as always on. As PIR systems continue to grow in size by adding more wireless nodes to their network, power consumption becomes a critical design factor, especially for battery powered applications. That's why it's important to choose low power devices for the signal chain, which allows you to save power at each step. Digital PIR solutions integrate steps one through three, leaving you with no flexibility to select the proper components to minimize power. We'll continue to analyze the differences between analog and digital PIR solutions as we step through the signal chain, starting first with the PIR sensor itself.

A PIR sensor is composed of two sensing elements that measure the difference in IR energy in the field of view of the sensor. The potential difference between the two elements is seen across the output of the sensor. Here, you can see an example of how the wave form tracks the movement of our little human.

As the body passes through each sensing element, and S shaped wave waveform is created on the output. PIR output frequency is very low at only 10 Hertz, and is also very small in amplitude. This means we'll need to amplify the signal to extract meaningful results from it, and that brings us to step two in our signal chain.

In step two, we perform signal conditioning on the PIR sensor output before it is to be read by an ADC. Two amplifiers are used as successive filter and gain stages to bring up the signal amplitude to a readable level while filtering out any unwanted noise at the same time. Note R1 and R2, which control the sensor current.

Typically, designers current-starve the PIR sensor in order to save power, but this comes at the cost of having the lower amplitude signal that requires more gain. In a digital integrated solution, you don't have the option to adjust the sensor current in case you needed more accurate readings. You also wouldn't be able to fully adjust the filter cutoff frequencies and the gain to your liking, although small variations are possible.

Looking at the blue box on the right, we see an example calculation showing how to choose the right amplifier for PIR signal conditioning, and we land at our first featured product, the TLV 8542. It consumes only 500 nanoamps per channel and is available in a tiny lidless package, making it ideal for PIR systems. Next, we'll look at the ADC that is responsible for the actual threshold detection.

First, you'll notice that there is a voltage divider from the ADC leading into our second amplifier. This divider sets the baseline output level and will correlate to a specific numeric code in the ADC. The ADC has an internal window comparator that can detect when our signal exceeds this code in either direction. These thresholds are programmable, given the designer full control on when to alert the microcontroller.

Here, you can see an example graph showing the sensor signal crossing the window thresholds, indicating motion. Once motion is detected, the ADC sends an alert to the microcontroller, which can then take an appropriate action depending on the application, such as turning on your lights. One important feature to note for the chosen ADC is that it can function without being controlled by a microcontroller, greatly saving power and making it ideal for battery powered applications like a PIR detector.

A digital PIR sensor integrates everything up to step three, which simplifies our circuit and saves board space, but comes at a loss of design flexibility. Digital sensors have a few programmable thresholds, but don't allow you to control sensor current or signal gain like a fully analog solution. Additionally, digital solutions result in a higher system cost.

Now, that we have a basic understanding of how a PIR circuit works, along with the differences between analog and digital solutions, we can look at further resources to help you design a PIR motion detection system. TI has many resources to help you out with your designs. Listed here is a low power PIR reference design, as well as a demo board containing a fully functional PIR circuit you can experiment with. TIs large portfolio or training, resources, and support all mesh together to make it easy to design an analog PIR solution for any application.

If you'd like to see more low power amplifiers to save power in your signal chain, make sure to check out the link above. We hope you learned some new tips on motion detectors and some new places to look for additional support. On behalf of the low power amplifiers and comparators team at TI, thank you for watching.