heAlTh & sAFeTy
walked around the office in different intervals, and the signal of the sensor was recorded. Figure 4 shows the sensor signal and a clear response to movement for the represented test run. On the left side, the intensity value is plotted, while on the right side, the change of intensity is shown. The intensity change corresponding to the movement is significant. In a second test, the evaluation board was
tested under more difficult circumstances. The test person stood still while allowing only very little motion to test the detection capability of not only movement, but also people presence. Figure 5 shows the signal and a clear intensity change.
Figure 3. Timing configuration of the ADPD1080 photometric front end.
Active infrAreD SenSing SolutionS Analog Devices’ ADPD1080 evaluation board, shown in Figure 1, realises active infrared tracking. The evaluation board consists of power
management, one photodiode, six leDs, and a photometric front end, the ADPD1080. The infrared leDs emit light, and the reflected intensity of the light is measured up to 5m away from the sensor. Movement can be detected by the change in intensity—when there is no motion in the room, the intensity is unchanged. The photodiode is centred between the leDs and can be placed behind a black dyed plastic screen, an added design feature providing a customer with the option for discrete placement. The evaluation board consists of two setups.
The first one is for closer proximities, and the second one works best for long-range distances. This is due to the leD intensity. The ADPD1080 is a full photometric front end with eight front-end inputs, which are connected to the photodiodes. It also has three integrated leD drivers and offers two time slots, which can be programmed independently to read out the photodiode and control the leDs. With those time slots, different modes can be enabled without reprogramming the registers to save power (about 20 per cent compared to the previous version). In addition, it has in-built ambient light rejection to filter for other light factors, such as sunlight, lamps, or other ambient light. even fluorescent light bulbs, despite their broad frequency spectrum, and leD luminaires, despite their switching frequency, are effectively filtered. Figure 2 shows a block diagram of the
ADPD1080. The current of the photodiode is amplified and converted with a transimpedance amplifier. Afterward, the band-pass filter and integrator are used for the ambient light filtering. The band-pass filter blocks the DC
light, and the integrator is used to filter out the AC component of the ambient light, reducing it by 80 dB. The working principle of the analogue front end is shown in Figure 3.
reAl-life MeASureMent ShowS the ADvAntAgeS The evaluation board was tested by mounting it on the ceiling of an office in multiple test environments. For each run, the test person
concluSion In conclusion, the ADPD1080 delivers an out- of-the-box experience, offering an active infrared presence detection solution that is not only low cost and highly accurate, but is also small in size. It operates at significantly lower power than time of flight or radar solutions, and can measure in a radius of up to 5m. Its robust features allow easy integration into existing products and in addition to presence detection, it can be used for a variety of use cases, including gesture sensing. Overall, the advantages can enable customers to improve efficiency and safety at reduced costs, thus helping to shape facility management in the future.
Analog Devices
www.analog.com
Figure 4. IR sensor response to walking motion: intensity value (left) and corresponding change in intensity (right).
Figure 5. IR sensor response to standstill position with limited movement: intensity value (left) and corresponding change in intensity (right).
FACTORy&hANDlINGsOlUTIONs | jUly/AUGUsT 2021 61
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