TDC1000: can we us this usecase for ultrasonic sensor ?

Hello Masaharu,

This depends on how the customer would like to implement the occupancy sensing. In any case, at these distances in air the PGA460 would be a better choice than the TDC1000. Do you know what method they plan to use?

Regards,

hi, Scott san.

thanks your reply.

could you more explain more detailed why PGA460 is better than TDC in air ?

what's method like ?

i know "how to place sensing transducer" , "how is the outside condition" are one of integral part for sensor which is the barrier for people who can't use it.

i'd like to know "desired thing" such as "sensing transducer has to be place inside of wall", sensing transducer can be place on the wall but need to be avoided to expose for watet, like something that.

all of thing for using ultrasonic sensor i'd like to know.

if i could summarize, let me ask customer to see.

Hi Takahashi-san,

Two air-coupled transducer sensor types are available, open and closed tops. I recommend the closed-top (such as the Murata MA58MF14-7N) due to the risks of the transducer being exposed to water.  Here is a description of the two types:

• Closed-top transducers are transducers which hermetically seal the piezoelectric

membrane from exposure to air or destructive particles. Closed-top transducer are favorable in applications that

are subject to harsh environmental conditions, such as exposure to outdoor elements, extreme temperature

changes, and debris. As a result of the additional protection offered by closed-top transducers, a transformer driven

method is typically required to maximize distance performance.

• Open-top transducers are transducers with vents or slots that expose the piezoelectric membrane to the air.

Open-top transducers are favorable for controlled indoor applications to minimize the risk of the transducer

becoming damaged. Open-top transducers do not require as much driving voltage as closed-top transducers to

achieve maximum distance performance; therefore, a transformer is not necessary.

Please read the PGA460 Ultrasonic Module Hardware and Software Optimization app note (www.ti.com/.../slaa732) for additional details.

The PGA460-Q1 can support closed-top transducers in the resonant frequency range between 30-80kHz, which is the ideal frequency range for this type of application since detecting people in the bathroom should be limited to a maximum distance of 2-3m. Both the TDC1000 and PGA460 use a time-of-flight ultrasonic measurement. This is mainly used to measure distance, but can also be used for occupancy detection. Typically, a Doppler-shift ultrasonic measurement is used to detect changes/movement in a room, which would be favorable, but TI's SENSING team currently does not offer a Doppler solution for ultrasound.

The transducer should typically not be obstructed by a wall or glass, but it is possible to detect objects through several mediums if mounted and coupled properly. Preliminary testing with the Murata MA58MF14-7N transducer shows object detection is possible through a 2.4mm thick sheet of polycarbonate and other plastics.

Since this approach uses ultrasonic time-of-flight, the sensor would need to be calibrated to the bathroom when no human is occupying the room. The no-human profile can then be compared to the calibrated threshold. The best approach is to compare a running history of ultrasonic return echo profile and/or ultrasonic measurement result to determine if there is movement within the bathroom. The problem is when the person remains still for too long, the sensor will assume no one is in the room, unless a combination of room calibration and echo signature change is implemented.

The ultrasonic time-of-flight sensor should be mounted higher so an object, such a box or rack of towels, doesn't block the sensor.