APPLICATION NOTE
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Test Bench for Ultrasonic Sensing ASSP
NCV75215
AND90239/D
Prepared by: Denis Zebrowski, Jiri Kantor, Dalibor Bartos
Summary

Nowadays ultrasonic time−of−flight measurement is
successfully used in industrial and automotive applications.
When reliability is a key aspect ultrasonic sensing has anadvantage over camera detection. Its performance inlow−visibility use−case is superior to infra−red cameras.
Due to small speed of an acoustic wave compared to
low−range radar or light ray in lidar, questions arise whether
it is worth to work on ultrasonic system that can mitigate
doppler−effect as the acoustic wave is more susceptible todistortion than the other mentioned mediums. Apart from
P215, the prerequisite for doppler radar is the ability toreliability determine and recalculate within milliseconds therelative distance based on the knowledge of doppler effectand the side−effects that it might be subject to. Dynamic
control of the frequency at the receiver and transmitter of
NCV75215 is already decoupled and the end−user should
reliability identify the frequencies that correspond to a given
relative speed and the distance between two objects.
onsemi, as a leading supplier of ultrasonic ASICs and thepresented ASSP, is committed to delivering state−of−the−art
sensing solutions for its customers.

Figure 1. Testbench Photo

Ultrasonic Measurement

The acoustic wave supported by the system is in the rangeof 35−90 kHz. In acoustics, the energy is described as soundpressure level (SPL). Acoustic wave propagation isa product of pressure created by vibrating a membrane ina gas. Frequency of vibration defines the frequency of the
wave. The change in pressure (p) is inverse−proportional todistance (r) (inverse−distance law).
p T 1rTime−of−Flight

Figure 2. Ultrasonic Time−of−Flight Basic
Representation

NCV75215 ASSP (short: P215) is designed to process
analog signal reciprocated from a nearby object and convert
it into a digital information about its relative position. It canwork with any ultrasonic transducer but the most used typeis piezoelectric. P215 performs time−of−flight (TOF)
measurement to detect the presence of and calculate theposition of an object.
Detection range depends on several components:
 Piezoelectric ultrasonic transducer
 Matching circuit
 Digital tuning Semiconductor Components Industries, LLC, 2023

September, 2023 − Rev. 0

The NCV75215 can be tuned to a distance anywhere
between 0.25 and 4 meters. As we will discover later,reverberations are the most crucial factor in the tuning
process. They occur naturally after burst pulses and decay
gradually over time. By monitoring them the ASSP canapply countermeasures which improve the range andreaction time. Under ideal external conditions and witha very−well tuned receiver, the ASSP can achieve detection
at a distance as low as 20 cm.

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Distance Estimation

Total reverberation time (tTX) is a result of TX burst pulse
count (npulses) and the carrier period (Tpulse), both of which
are configurable in ASSP’s software.

Distance (d) is a product of measured time interval (techo)
between burst pulse transmission and echo reception, and it
is defined as half of the round−trip time of an ultrasonicpulse. Ambient temperature (Tamb) affects the density of
atmospheric air and thus speed of acoustic wave (vsound).
The exact speed depends on the wave’s period.

t TX + T pulse @ n pulses(eq. 2)Carrier period is defined by the oscillation frequency of
the TX driver.

@ v soundtd + echo
2

Equivalent Circuit

The piezoelectric circuit model can be represented asa structure of 2 resonators: serial and parallel. Both paralleland serial resonator should be tuned to the nominal resonant
frequency of the piezoelectric transducer. Moreover,a tunable transformer can be selected to increase flexibility.

Where:
v sound ^ 346 m
s for T amb + 25C

(eq. 1)

E.g., for an object 1 meter away from the sensor, a burst
pulse reaches the object after approximately 5.78 ms.

Serial Resonator

The resonant frequency of the circuit is defined by theserial resonator, i.e., transducer and can be calculated using
its inductance (Ls), capacitance (Cs) and Thompson’s
formula.

Reverberation

NCV75215 measures the reverberation period and thetotal length of the reverberation for diagnostic purposes.
Based on this information the system can detect faults in thepiezoelectric sensor.
Reverberation, depicted below, is a byproduct of burst
pulse transmission. Thus, the control over the transmitted
number of periods as well as the control over amplitude ofthe drive current is essential to accurately measure time offlight.
Multiple echoes are created and received at different
timestamps by the transducer due to multipath effect.

Figure 5. Equivalent Resonant Circuit of Transducer

Where:
fR = 48 kHz, Cs = 80 pF, Rs = 1 kW, Ls = 138 mH,
CP = 1.7 nF.
Figure 3. TX Burst Pulses, Reverberation, Echoes

Below Thompson’s formula is applied to obtain resonant
frequency. The values correspond with the picture.
f+

Reverberation
too long
Rp value ok,minimalreverberation(eq. 3)

Parallel Resonator

The same formula is applied to the parallel circuit model(Lp, Cp). Additionally, parallel resistance (Rp) significantly
affects the reverberation time. Steps to tune parallel circuit:
1. Choose parallel resistance (Rp) to minimize
reverberation time
2. Tune transformer and adjust parallel capacitance(Cp)

Chattering appeared
TX

1
1
+
+ 48 kHz2p ǸL sC s
2p Ǹ(80 @ 10 *12) @ 0.137

Reverberation

Figure 4. Reverberation Scenarios,
22 TX Pulses + Reverberationwww.onsemi.com
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Trilateration and Object Detection

In the last step, calibration is necessary to assure thecorrect behavior of the overall system.

The goal in trilateration is to map an object on thecartesian plane defined by sensors. Two TOF measurements(d, i), below formulas (l1, vt) and knowledge of physicalproperties of an acoustic wave is sufficient for mapping.

Direct vs. Indirect Measurement

Direct measurement is performed by the sensor which
generates ultrasonic burst signal. Other sensors found next
to it indirectly receive the reflections of the signal as itreciprocates under different angles in several directions(multipath propagation). Depending on object’s position
relative to sensors, the echo’s magnitude at the receiver willvary among them.
During one measurement cycle, software analyses thereceived data from the sensors and determines the positionof obstacles with the use of trilateration algorithm. It can use
the data from two or three sensors. Starting from sensor S1,
each next sensor transmits burst pulses.

Figure 6. Trilateration Calculus
l 1 + d * i ) l [m]
2@l
2

2

2

v t +" Ǹd 2 * l 1 [m](eq. 4)2

Once TOF is measured, the formula to find the distance toeach sensor is simple. Applying trilateration is done by thecentral processing unit which collects the data from all the
sensors.

Figure 8. Direct and Indirect Measurement − 1 Cycle

It is necessary to utilize indirect measurements intrilateration. The measurement is arbitrated by the sensor
responsible for sending ultrasonic burst signal. The end oftransmission marks the start point of TOF measurement. The
reception of direct and indirect echoes is logged by eachsensor and reported to the master device. Distance between
the sensors and the object is used for precise object
localization.

Figure 7. Extracting TOF Values using
onsemi NCV75215

Indexes denote: tt1−o1−r1 – TOF of a signal sent by sensor 1,

Figure 9. Measured vs. Calculated TOF Values

reciprocated by object 1 and received by sensor 1,
direct measurement. See variable d above tt1−o1−r2 – TOF of a signal sent by sensor 1,
reciprocated by object 1 and received by sensor 2,
indirect measurement.

Time data is defined as per following equations:tDirect (sensor1) : t t1*o1 + t1*o1*r1
2Indirect (sensor2) : t t1*o1*r2 * t t1*o1

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By using multiple sensors and indirect signals (multipath
effect) more advanced use−cases, such as park assist, arefeasible.

Figure 12. Overlap between Viewing Areas

The Figure 13 shows a sequence consisting of 9 steps
during which the overlap point between signals from 2
sensors and in effect length vt is found.

Figure 10. Car Park Assist Use−caseConfirmation Algorithm

Selection of algorithm type depends on the end
application and complexity of the measurement. In general,
double confirmation scheme offers more robustness as it
requires less sensor signals. However, if the intention is toachieve maximum accuracy, the measurement area isnarrow and placed centrally, a triple confirmation scheme isrecommended.
Double confirmation scheme:
 Input from 2 sensors sufficient wider detection angle,
 better minimum distance, Faster confirmation but more false positives.
Triple confirmation scheme:

 Input from 3 sensors

 narrower detection angle,
 worse minimum distance,

 Slower confirmation but more stable, i.e., fewer false
positives.

Figure 13. Measurement and Localization
using Trilateration − Sequence

The multi−sensor approach enlarges the detection area
compared to one sensor always acting as a transmitter. It also
discards false echoes more efficiently as it requires object
confirmation from at least 2 sensors in 2 consecutive
measurements (double confirmation algorithm). In the caseof simple use−cases, such as occupancy detection, where
narrow viewing angle is sufficient, single−sensor approach
can be used.

In the study, only the double conf. algorithm is evaluatedin detail. In principle, an object is successfully localized if
the coordinates calculated from both pairs of sensors (sensor
1 + 2 and sensor 2 + 3) overlap within the tolerance region.
This setting is particularly good for obstacles in shortdistances, it can find the position if the obstacle is just 25 cm
away from the sensor.
The triple confirmation shows better results for longer
ranges, i.e., exceeding 3 meters. Data from all three sensors
is used to find the position of the obstacle. It is more stable
and less susceptible to false echo position detection.
Because all three sensors need to see the obstacle, theminimum distance at which it can localize the obstacle isfurther away (approx. 35 cm) but it strongly depends on thetransducer.
Software implementation of both methods is defined intrilateration.cpp.

Figure 11. Sensor Viewing Area

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Moving objects with uneven surfaces might yield
different results in 2 consecutive measurements. For thealgorithm to accommodate such use−cases it is necessary to
identify tolerances and define spatial boundaries within
which the object is labelled as found.

close to RX pins. Also, the analog ground plane (GNDA),
that these components are connected to, should be separated
from the digital ground on the right side of NCV75215 EVK.
To prevent the electromagnetic field (EMF) of the RX pathfrom coupling the surrounding noise, the RX path should berouted inside of the poured GNDA polygon that acts as EM
shielding. These routing practices help to achieve a better
signal−noise ratio (SNR) at the receiver.

Figure 15. Top Layer

Figure 14. Human Detection RequiresFine−tuned Algorithm

To summarize:
1. For detection of the object in two−dimensional
space at least 2 sensors are mandatory.
2. To confirm location of the obstacle at least 2
consecutive measurements by each sensor arenecessary.
3. It is essential to confirm the sensor’s viewing
angle and resulting detection range on testbench ifother than recommended sensor is to be selected.

Figure 16. Bottom Layer

P215 Evaluation Kit

The schematic is based on the recommendations from thedatasheet. Auxiliary elements include center−tapped
transformer connected via its primary side to TX driver’s
output pins (DRVA/B/C). The secondary side feeds thepiezoelectric element and connects via the matching circuit(C4, R5) and capacitive coupling (C1/5) to RX input pins.
No EMC filtering is available.
Receiver Path Routing

Figure 17. RX Part of PCB

The external components of the receiver are located on theleft side of the ASSP and are recommended to be placed

Figure 18. Sensor Board with NCV75215
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Test Pins

Table 1. POWER CONSUMPTION

Test pins TST 0−3 serve for application debugging. TST2
and TST3 are PDM debugging ports that allow to observe
echo magnitude, detection etc. A full list is provided in the
NM Register Control tab of P215 Qt graphical interface.
PDM debugging ports are filtered by a 2nd order LPF. In
end−design these pins should be connected to digital groundas they can pick up noise, due to high−speed signal slopes.

Number of Sensors

Power Consumption [mA]0, no USB71

0, USB

79

1

83

2

90

3

94

Assembled Demo Boards

The demo sensor board is based on NCV75215 modulefrom onsemi and was tested with Murata 58 kHz
MA58MF14−7N transducer. Recommended list oftransducers can be found in the datasheet of NCV75215.
To achieve optimal reverberation time, we calculate thevalues of the parallel resistor and capacitor in the matchingcircuit.
Matching Circuit(Rp, Cp)
Test pins:
TST 0−3
I/O Line
Transformer

Figure 21. Complete Setup with 3 Out of 4 Sensor
BoardsFigure 19. Sensor Demo Board

The boards work correctly if the serial port of theconnected master board is displayed in Trilateration demo
software.

The master board connects to the sensor boards via four(4) NCV7321 LIN transceivers from onsemi. An Atmel
AVR32 microcontroller controls the measurement, extracts
the detected echoes from sensors (NCV75215 slave
modules) and sends them to the PC software for analysis.

Figure 22. Connection Successful

4 x NCV7321
LIN Transceiver

NCV75215 ASSPThe ASSP device controls the ultrasonic transducer (Pz1)
via a transformer (Tr1). The receiver’s path impedance isdefined by the matching circuit (C3). Additionally, EMC
filtering (CF1, RF1, RF2) is added before the input pins.
Moreover, 2 capacitors (C1, C2) serve as capacitive
coupling of the receiver.
The blocks in the diagram represent the functionalities
constituting either the analog front−end or digital signal
processing (DSP) unit. The analog signal from ultrasonictransducer is amplified (LNA & VGA), converted to digital(ADC). At the digital side, the signal is filtered (BPF) before
comparing it to a time−dependent threshold (Threshold
control) which defines the detection threshold of an echo.

Figure 20. Master Demo Board

Up to four (4) NCV75215 modules can be connected tothe main master board. The master board requires approx.
12 V and 100 mA. Depending on the number of connected
sensors the current consumption will vary.

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The echo is reported on I/O Line (IO Line transceiver)when the signal magnitude exceeds the threshold.
Steps and corresponding output signals:
1. Receive analog RX signal  RX analog
2. Convert analog RX signal to digital
3. Amplify it with dynamic gain (VGA)
4. Apply filtering  Echo Magnitude
5. Apply threshold detection  Echo Envelope
6. Debounce  Echo Detection
Figure 23. ASSP Diagram

Figure 24. Signal Processing Block Diagram (Ref. Datasheet)
Supply Voltage, Drive Current, Burst Power Saturation

The Figure 25 shows an example of drive current andsupply voltage characteristic of the NCV75215. The
minimum voltage level (Vsupmin) defines the transmit power
for the transducer. If the transducer’s equivalent serial
resistance (RSmax) is too high, it limits both Vsupmin and thus
drive current (ITX) as per the characteristic.

Figure 25. Example of Vsup (ITX) Characteristicwww.onsemi.com
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The relation between the transmit current and voltagechanges, depending on the transformer and the impedanceof its primary winding.

The transformer acts as a push−pull converter for thetransmitted burst pulses and received echoes. The center tap(CT) of the transformer divides the primary coil in half. The
voltage measured between one end and the center tap of the
primary side is N times higher on the secondary side. Thiscan be calculated as follows:
V sec +N sec
@ V inN pri,CT

Example:Nsec = 8, Npri,CT = 1 (1:1:8), VDRVA, B = 2 V  Vsec = 8 V.
Figure 26. Center−tapped Transformer

Transformer Requirements

The NCV75215 controls a piezoelectric membrane thatvibrates under applied drive current (ITX). Tuning to thedesired frequency is only possible if the components werechosen correctly. We present the typical values of thetransducer and transformer for a given resonant frequency.
Typical values: Secondary inductance: 3 to 5 mH,
 Rdc Secondary: 25 to 50 W,
 Rdc Primary: 1.6 to 2.5 W,
 No. of turns ratio (priA:priB:sec): 1:1:8 to 1:1:11.

Figure 27. Transducer Murata MA58MF14−7N 58 kHz

We should adjust transformer turn ratio and resonant
circuit characteristics to avoid the saturation of Vsup voltage
which eventually leads to lower transmit power. Minimum
supply voltage (Vsupmin) is described as follows:
V supmin + V ȀDRVC
V Smax +V DRVC

On

On

Transducer & Matching Circuit Requirements

Typical values: Resonant frequency: fR = 48 to 58 kHz, Parallel capacitance: Cp = 22 pF to 4 nF,
 Parallel resistance: Rp = 3 to 8.2 kW,
 Series resistance: Rs = 1 to 2 kW.

) V DRVA,B ) V Smax

R Smax @ I TX
N2
+ R DRVC

V supmin + V DRVCOn

On

The evaluation kit works both with tunable andnon−tunable transformer. Parallel resistor (RP) andcapacitor (CP) correspond to R5 and C4 respectively(schematic).

@ I TX@ T TX ) V DRVA,B )R Smax @ I TX
N2(eq. 6)

Where:RDRVCOn − switch on resistance at TX driver output C(center of the winding),
ITX − TX current,
VDRVA,B − voltage between TX driver output A and B(primary winding),
Rsmax − transducer maximum equivalent serial resistance,
N − transformer turn ratio e.g., 1:1:8  8 (step−up 8 times),
Vsupmin − TX voltage (secondary winding).

Figure 28. Transformer and the Matching Circuit

An example of how to calculate the minimum supply
voltage to avoid TX saturation.

Detection Threshold

Threshold is part of digital signal conditioning, and it
defines a minimal magnitude level of a received signal atwhich the received echo signal is detected as an object.
Anything below the threshold value is ignored.

Known values: ITX = 350 mA (maximum), RSmax =1000 W, N = 8 (1:1:8), VDRVA,B = 2 V, RDRVCon = 3.7 W(maximum).
V supmin + 3.7 @ 0.35 ) 2 ) 1000 @2 0.35 + 8.76 V
8

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IO Line Data Communication

Threshold curve is linearly interpolated and consists of 12
sections − for each section, a level and its duration are
specified.

An IO driver controls the IO line to provide
communication between an ECU and the NCV75215.
IO Line Properties:
 3.3 kbit/s baud rate, 8−bit checksum, Pulse Width Modulation (PWM) bit coding, 4−bit addressing.
There are 3 types of communication that are possible with
NCV75215:
 Standard: reports reverberation and echo with their actual
width by pulling the bus voltage down to ground, Echo reporting: reports the same information with shortpulses thus optimizing the bus usage,
 Advanced: no echo reporting on the bus while themeasurement is ongoing. Instead, data communication isused afterwards to encode the information about the peak
duration. This method also reduces disturbances on thebus and in DSP.

Figure 29. Threshold Curve (ref. Threshold)Low state on the bus is used to encode information(zero−dominant) when the bus transmits in advanced mode.
IO−Line encoding takes place in a predefined fixed−timeframe and is analogical to LIN communication. This modeis enabled via register 10− “Advanced IO Line protocol
enable” bit.
Rising and falling edges have slope control function to
reduce EMI radiation. This slew−rate control is disabled(IO_SLP high) after 60 ms (typical, TSLP_IOL).
During the measurement cycle, the driver asserts a low
level (IO_CMP) on IO Line (IO) which indicates that anecho is detected. After the end of measurement cycle theinternal logic turns the control block off.

Figure 30. Example of Threshold and RX Signal on
Oscilloscope
Dynamic RX Gain

Dynamic gain is part of analog signal conditioning and isessential to keep the received analog signal within the
dynamic range prior to digital processing steps. Gain iscontrolled dynamically so that weaker echoes that arrive
from more distant objects are interpreted correctly. Thismethod enlarges the detection area of a sensor.
Dynamic gain shown in Figure 31 consists of 5 sections.
Each of them is defined by starting gain, gain delta and time
duration.

Figure 31. Dynamic Gain Curve (ref. Datasheet)

Figure 33. Single Data Frame used by Advanced
IO−Line Mode

The integrated low−side driver requires an externalpull−up resistor (R4) connected to VSUP.

Figure 32. Example of Dynamic Gain and RX Signal
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Mastercommand

TX Signal +Reverberation

Echo #1

Echo #2

THRESHOLD

pulse
RX Signal
MAGNITUDE

Standard
High recessive idle level (pull-up)

Red line is controlled by sensor.
echo width

Echo reporting (Pulse)
Low dominant level

Pulse: 99.2 us

Advanced IO Line (LIN similar)

Diagnostic
pulse
TOF #1
End of measurement
Start ofmeasurement

TOF #2
Measurement duration

Figure 34. IO− Line Communication − Standard, Advanced, Echo Reporting

T<TSLP_IOL
IO

by master

T<TSLP_IOL

T=TSLP_IOL

by sensor

T=TSLP_IOL

by sensor

IO_DRVIO_SLP
IO_DRV_ENA
TSLP_IOLTSLP_IOL

Figure 35. Timing of IO−Driver Inputs/Outputs. Example: Sensor controls the IO Line

R2

D1

P215 ASSP

VSUP

VBAT

~300 kW

+
CMP

R4
C6

C7

C8

IO_CMP

IO
R3Control

IO LineC9

IO_DRVIO_SLP
IO_DRV_ENA

Figure 36. IO−Line Internal Driver with External Network

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Qt Application consists of 3 Windows:
1. “Measurement” menu − basic control of themeasurement such as start/stop.
2. “Triangulation” menu − presents the results ingraphical form in cartesian coordinate system.
3. “NM Controller (NM)” menu − configures
EEPROM registers.

Table 2. PARAMETERS OF IO/LINE COMMUNICATIONPROTOCOL
Parameter

Min

Output Slew Rate
I/O Short Circuit Current

10

Pull−up Resistor

200

Duration of slew rate control

Typ.

Max

Unit

0.5

0.8

V/ms

50

mA
kW

60

ms

IO line recessive current
consumption

150

mA

IO line dominant current
consumption

600

mA

Master MCU Firmware

Figure 37. Three Application Windows

The MCU controls the measurement, extracts the detectedechoes from sensors and sends them to the PC software foranalysis.

Although the software references “triangulation”, theunderlying method is based solely on trilateration
principles. No angle is measured or calculated in the process.

Front−end Qt Application

This tool communicates with AVR32 microcontroller
over the serial line (UART).
Configurations include: Resonant frequency, Measurement mode, Threshold and dynamic gain,
 IO−Line settings.

Figure 38. Trilateration Real−timeMeasurement Window

Figure 39. Measurement Period and Duration Values in Qt Software, NM Controller

Start/Stop Continuous Measurement
Perform Single Measurement

Sensor location [x, y] relative
to sensor 1

Algorithm/trilateration
settings

Figure 40. Measurement Configuration Window
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Figure 39 shows: “Measurement period” setting influences the speed atwhich the measurement is repeated. It must be longer thanthe “Measurement duration” in “NM Controller”
window.
 “Memory threshold” & “Memory tolerance”− notimplemented.
 “Algorithm tolerance” − specifies tolerance for declaring
confirmation during comparison of 2 consecutive
measurements from the same sensor.
 “Intersection tolerance”− used by triple confirmation.
Object is detected upon intersection  tolerance ofarches/circles. The radius of a circle is equal to the
distance from an object to each sensor.
 The coordinates refer to the position of the sensors
relative to sensor 1, i.e., [0, 0].
 “Adaptive axis range” setting is used for measurements atlonger distances.

Figure 41. Test Pin Signal Assignment, NM Control

In register 10 (REG10) sensor current or reverberation
debounce time are among the settings that can improvereaction time and detection range. Users might decrease
sensor current to avoid saturating TX power which could
lead to longer reverberation time and chattering effect.
Debounce time is another measure to tackle this issue andimprove robustness. Remaining parameters in REG10 deal
with reverberation monitoring and digital post−processingof the received echoes.

“NM Controller” menu from Figure 42 offers optional
advanced configuration of NCV75215 through its 16
registers in EEPROM. For basic demonstration purposeswith an object in specified range it is not necessary to modify
their content, nevertheless several settings that help to
optimize the measurement are demonstrated.
The value of duration is stored in register 4 (REG4). The
period must be greater than meas. duration.
The selection of test pin output signal is stored in register
15 (REG5).
 Echo detection,
 Echo magnitude, Echo threshold, Echo gain.

Figure 42. Reverberation Control and Additional
Settings, NM Control

Pin 0 can be changed between amplified differential
signal from transducer (“RX Analog”) or high−impedance
signal from the transducer passed through a pull−up resistor(“HiZ”). Pin 1 can be skipped.

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Table 3. ADDITIONAL PARAMETERS TO IMPROVE PERFORMANCE, REGISTER 10 SETTINGSNM Window Label

Description

 Reverberation / Decay Monitoring Window Duration
 Monitoring window start Monitoring window step

Reverberation monitor: start time, duration,
and accuracy. Should be set accordingly tosensor’s behavior.

REVERB_MON_DUR[8],MON_WIN_START[12],MON_WIN_STEP[2]Software Variable (REG10)[duration, start,step] =
[409.6, 0.0,
204.8]

Default State

Reverberation period Variation
Limit

In case variation is above specified limit error
flag is set. Serves as automatic sensor check.

REVERB_PER_VAR_LIMIT

5.4%

Noise suppression Enable

Measure to improve Signal−Noise−Ratio

NOISE_SUPP_ENA

1

Automatic carrier period control

Ensures the optimal sensitivity and SPL of thetransducer over temperature, instead ofmanual tracking of reverberation frequency.
Might require higher IO−Line bandwidth toduring active measurement.

CARRIER_PER_AUTO_ENA

0

DSP Filter auto Q factor control
enable*Automatic control of Q factor. Measure to
improve detection performance during
dynamic ranging and at longer distances.

AUTO_QF_CTRL_ENA

Automatic echo debounce time
control enable

Improves detection during dynamic ranging(similarly to auto Q factor control). Use onlywith auto Q factor control and adaptive axis
range enabled.

AUTO_ECHO_DEB_CTRL_ENA

0, fixed Q = 50*Higher Q results in less losses at the resonator due to more damping of parasitic frequencies (acts as a filter) and effectively in better SNR.
It is recommended for greater detection distance thus echo detection in dynamic environment can be improved.

the receiver’s sensitivity should be readjusted. This can bedone using temperature reading from the pins connected tothe transducer and stored in register 0. This value can be used
to return the RX gain and for automatic carrier period control(see above).

Figure 45. Transducer Temp. Reading is Possible
over Connected Pins

TX & RX period can be controlled independently fromeach other which makes it possible to turn the P215−based
system into doppler radar.

Figure 43. Dynamic Gain Values, NM Controller

Register 5 and 8 store gain and threshold values. The
curves are modelled underneath using linear interpolation.

Figure 46. TX & RX Period can be Controlled
Independently
Back−end C++ Application“Measurement.cpp” contains the functions that are called
within “Measurement” menu in Qt application. Except forbasic start/stop measurement command, it provides
interface to set more advanced meas. parameters such as
meas. period. The data received from Qt app. is passed to theother two C++ applications which are explained in the next
sections.

Figure 44. Threshold Register Values, NM Controller

Tracking of transducer temperature is especially usefulfor keeping the performance of the transducer flat overtemperature. Due to change in temperature, SPL varies, andwww.onsemi.com
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Finding Obstacles“Trilateration−cpp” defines functions that analyze themeasurement data samples and calculate the position of

obstacles with use of selected algorithm. Both algorithms
are supported by the code.

Figure 47. Data Processing between MCU and Qt GUI in measurement.cpp
NCV75215 Configuration & Control

executes the user commands coming from the Qt application
and reports back the register status when possible. Beside
read/write register operations, C++ source file contains alsofunctions to control status LEDs of the master board via DIO
pins.

NM Controller is a graphical interface that wraps up thefunctionalities defined in “tmccontroler.cpp” C++application. Registers R0−R15 of NCV75215’s EEPROM
are read and written by AVR32 MCU over IO−Line. AVR32

Figure 48. Snippet of Double Confirmation Algorithm Loop in “trilateration.cpp”

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Measurement Test Bench“P215_EVK_V1” sensor boards are connected in star
topology to “P215_TRIANG_V1” master board. Three

sensors are sufficient for demonstrating trilateration,
whereas 4 sensors increase the detection area.

Figure 49. Top View Drawing

Figure 50. Front View

Figure 51. Side View

Figure 52. Top View

Trilateration Range

The maximum detection range was limited due to thelaboratory’s constrained environment. Nevertheless, it can
provide insight into system’s capabilities in complex
use−cases with multiple objects that can reflect the acoustic
wave.
For test purposes we focus on demonstrating
out−of−the−box detection performance of the ASSP.
Therefore, only default configuration was used to generate
results. Results showed that depending on the object’s
position, the detection range varies. It reaches its maximum
point of 2.8 meters midway of the testing area.

Figure 53. Object Detection Range
Measured in the Lab
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Measurement Period & Duration

Threshold Visualized

Measurement period and cycle are shown below with 3
IO−Line Vbat signal curves (yellow, green, purple) − eachassigned to a different sensor. To represent meas. duration,
we use an additional diagnostic signal (pink) indicatingwhen the measurement is ongoing. The measurement cycle
consists of 3 meas. periods. Each period is configured bydefault to last 24 milliseconds. Three sensors transmit inalternating round−robin fashion.

The threshold curve (red) is a digital reference signal
compared with echo’s magnitude. Its purpose is to filter out
irrelevant echoes. In the case of objects located further away
there is a visible difference in arrival time and magnitude ofan echo. The green curve starts with TX burst pulse fromsensor 1 followed by multiple echoes. Three identical red
shapes correspond to 3 measurement periods, i.e., TX+RX
slots − each reserved for different sensor.

Figure 54. Measurement Duration, Period, and Cycle

Figure 56. Pole 70 cm Away, Threshold andMagnitude, Measurement Duration of 24 ms

When the first sensor is in direct measurement mode, itsbattery voltage drops during the transmission of burst pulses
by approx. 1.1 V and recovers to its nominal value (bluecurve) of approx. 12 V. IO−Line communication isdependent on the battery/power supply voltage level. We
observe several square−shaped voltage drops (red curve).
The first low voltage state represents TX transmission
followed by a few dips indicating detected echoes, each ofdifferent length. Yellow and green curves represent the same
behavior for the second sensor. The measurement period forboth signals in the case is 30 ms.

Figure 57. Pole 2.3 m Away, Threshold andMagnitude
Dynamic Gain

The gain curve defines the sensitivity of the receiver path,i.e., the amplification of the analog RX signal. Like thedetection threshold, the gain curve is also fully configurable.
Gain value is set based on the knowledge of the relation
between signal attenuation and distance.

Figure 55. Echo Detection Encoding on IO−Linewww.onsemi.com
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AND90239/D
Provided evaluation software can be used to measure
reverberation without oscilloscope. Register 1 (REG1) in
EEPROM memory is a designated area that stores this value.
The supported frequency range of the transducer is30−95 kHz. Below we analyze the reverberation time withdifferent carrier frequencies (TX−RX Period, REG2A) andburst pulse count (TX Pulses, REG3) given the default
current of 350 mA. When the nominal resonant frequency of
the transducer (orange) is juxtaposed, it almost overlaps
with the lowest reverberation time. This indicates that thesystem is calibrated well to the nominal frequency. The
pulse count’s impact on the reverberation stays constantfrom 8 pulses onwards and it changes by 450 ns between 0
and 31 pulses.

Figure 58. Dynamic Gain, Echo Magnitude
Reverberation

As a part of diagnosis, we observe the control signal of thepiezoelectric transducer followed by reverberation (red).
Impedance signal (blue) characterizes the sensor’s responseto stimuli, and it is valuable information for diagnosinginternal sensor faults, polluted surface, or detached state.

Figure 61. Reverberation vs TX Frequency

Figure 59. 140 ms Reverberation

Figure 62. Reverberation vs Burst Pulses

It is recommended to calibrate the system according to thenominal frequency of the transducer. The second calibration
step should focus on the measurement range expected in thefield. Detection and reaction time at 0.25 m can be improved
by lowering the number of pulses and dynamic gain incontrary to 4 m, which requires more transmit energy andhigher sensitivity/RX gain of the receiver.
Figure 60. Detached Sensor

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AND90239/D
RX Signal Processing & IO Line Communication

Measurement with Multiple Sensors

The analog signal is processed through several analog anddigital stages before an object is. Using provided test pins
(TST2, TST3) we can observe selected intermediate signals.

The test setup consists of 3 sensors and 1 object. Every
cycle consists of 3 measurements during which 1 sensor acts
as a transmitter. To detect an object, i.e., label it with a dot
as shown later, any 2 out of 3 sensors should confirm its
presence. The role of transmitting sensor rotates between all
3 of them in round−robin fashion (blue, red, yellow spike).
The data frames are sent to the central master unit via
IO−Line after each measurement cycle.

Figure 63. Analog Echo Signal is Amplified andProcessed Digitally

Detection signal is a square−shaped pulse of variable
duration that is directly encoded onto IO−Line. It resembles
a binary signal that indicates either the presence or absenceof an object at a certain distance.

Figure 66. Echo Envelopes for 3 Sensors.
S1, S2, S3 Transmit Burst Pulses

During 1 cycle each sensor performs 1 direct (TX & RX)
and 2 indirect (RX only) measurements. Two sensors are
sufficient to confirm an object.

Figure 64. Echoes with Magnitude below
Threshold are Discarded

Figure 67. Echo Envelopes for 3 Sensors.
S1 Transmits Burst Pulse

Figure 65. Detected Echoes are Encoded
onto IO Line

Figure 68. Echo Magnitude Signals compared to theThreshold Value
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AND90239/DWith more relaxed values of the confirmation tolerances
the system’s response time might be faster. This comes at thecost of accuracy. Side−effects might occur if an object ismoving, or it has a complex/uneven surface. In such a case
2 pairs of sensors might detect the same object at slightly
various locations which leads to duplicates. The
visualizations were performed for default measurement
settings.
Triple Confirmation

The detection with 3 sensors in 2 consequent
measurements is more demanding in terms of object’s shape.
Especially asymmetrical shapes might seem problematic toconfirm. Therefore, it is recommended that sensors face thecritical area directly and not under an angle. In Figure 72 andFigure 73 we highlight two different behaviors of thealgorithm without a change in placement or configuration.

Figure 69. Echo Detection Signals from 3 Sensors
Visualization − Double Confirmation

Objects reported by solely 1 sensor are labelled as
unconfirmed and are visualized by a blue arch with theradius of the measured distance.
If an overlapping point of 2 arches is found in 2
consecutive measurements, the point is labelled with a dot.
This indicates that trilateration algorithm determined theobject’s exact position (within the tolerance range) byconfirming the distance with 2 sensors.

Figure 72. Chair 160 cm away, Detected

Figure 70. Pole 70 cm away, Visualization, Correct

Figure 73. Chair Detection Failed

Measurement data containing echo magnitude is stored in
Register 12 (REG12) and is plotted underneath.
Figure 71. Pole 2.3 m away, Visualization, Duplicate

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AND90239/D
Transformer Characteristics

We analyze input and output voltage signal of thecenter−tapped transformer. It receives burst pulses withtransducer frequency of 56 kHz from TX driver. Voltage is
stepped up according to the transformer ratio and current
drops accordingly from the set value of 350 mA.

Figure 74. Measurement Data in EEPROM

As discussed previously, double confirmation suffersfrom side−effects such as duplicates. This can be mitigatedwith the triple confirmation algorithm if its shortcomings are
acceptable in targeted use−case. Below we depict how bothalgorithms perform in the case of the chair placed centrally
at 160 cm.

Figure 77. TX Driver Output Pins DRVC (center−tap,
C2−purple), DRVA/B (top/bottom, C1−yellow)

Figure 78. Transducer Input Signal

Expected theoretical transducer voltage can be calculated
according to the previously presented formula. The step−up
ratio based on the measured voltages is equal to N = 8.36.
Figure 75. Single Object Detected, Triple Conf. Alg.

Figure 76. Mirrored Detection from 2 Pairs of
Sensors, Double Conf. Alg.
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AND90239/D
LIST OF ABBREVIATIONS
HW
SW
TX
RX
TOF
SPL
ASSP
ASIC
ECU
MCU
DSP
BPF
LNA
VGA
EMF
EMC
SNR
EVK
EVB
PWM
UART
EEPROM
PCB
BOM
IO
REG
GND
DRV

− Hardware− Software− Transmitter− Receiver− Time of Flight− Sound Pressure Level− Application Specific Standard Product− Application Specific Integrated Circuit− Electronic Control Unit
− Microcontroller Unit
− Digital Signal Processing− Band Pass Filter− Low Noise Amplifier− Variable Gain Amplifier− Electromagnetic Field− Electromagnetic Compatibility− Signal Noise Ratio− Evaluation Kit− Evaluation Board− Pulse Width Modulation− Universal Asynchronous Receiver−Transmitter− Electrically Erasable Programmable Read−Only Memory− Printed Circuit Board− Bill of Materials− Input Output− Register− Ground− Driverwww.onsemi.com
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AND90239/D
APPENDIX 1

Figure 79. Triple Confirmation Algorithm in C++

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AND90239/D
APPENDIX 2

Figure 80. Master Board Schematic

Figure 81. Master Board Dimensions

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AND90239/D

Figure 82. Master Top View

Figure 83. Master Bottom View

APPENDIX 3
Table 4. SENSOR BOARD/SLAVE BILL OF MATERIALS
Description

Quantity102−3035 SIL SOCKET 2 pins, matches 102−2218 header (made of breakaway SIL32 socket); D01−9973242; HARWIN;
RoHS=Yes (repl. for 366−5707, 176−371)2

109−7981 SCOPEGND; WIRE BRIDGE, made of 1/36 FCI - 75160−105−36LF - HEADER, 1ROW, 36WAY

1

114−0813 RESISTOR NB_0805_1.22K_0.1W_0.1%; RN73C2A1K21BTG ; TYCO; RoHS=Yes

1

116−9632 SMA RIGHT ANGLE JACK GOLD plated; 19−49−5−TGG; MULTICOMP; RoHS=Yes

1

145−9029 DIODE; SWITCHING 200 mA/75V; BAS16HT1G; onsemi

1

171−4769 Capacitor 100uF/50V, low ESR=0.18R; EEEFP1H101AP; PANASONIC; RoHS=Yes

1

175−9285 Capacitor MLC−X7R_0805_680pF_10%_100V; MCCA000404; MULTICOMP; RoHS=Yes

2

175−9293 Capacitor MLCC−X7R_0805_4.7NF_10%_100V; MCCA000411; MULTICOMP; RoHS=Yes

1

301−9846 Capacitor MLC−X7R_0805_330pF_10%_50V; 2238 580 15616; PHYCOMP; RoHS=Yes

1

301−9858 Capacitor MLC−X7R_0805_470pF_10%_50V; 2238 580 15618; PHYCOMP; RoHS=Yes

4

301−9949 Capacitor MLC−X7R_0805_100nF_10%_50V; 2238 580 15649; PHYCOMP; RoHS=Yes

3

933−2375 RESISTOR MF_0805_100R_0.1W_1%_100V; MC 0.1W 0805 1% 100R; MULTICOMP; RoHS=Yes (repl. For
911−732)2

933−2383 RESISTOR MF_0805_1K0_0.1W_1%_100V; MC 0.1W 0805 1% 1K; MULTICOMP; RoHS=Yes (repl. for 911−859)2

933−2391 RESISTOR MF_0805_10K_0.1W_1%_100V; MC 0.1W 0805 1% 10K; MULTICOMP; RoHS=Yes (repl. For
911−975)5933−3150 RESISTOR MF_0805_390R_0.1W_1%_100V; MC 0.1W 0805 1% 390R; MULTICOMP; RoHS=Yes (repl. For
911−800)

1

CUSTOM TRAFO SMD, primary 3 leads, secondary 2 leads

1

DK:277−2415−ND CONNECTOR HEADER, PCB, HORIZONTAL, 3.5MM, 300V/8A, 3WAY; MC 1,5/3−G−3,5 (1844223);
PHOENIX CONTACT; RoHS=Yes

1

DK:277−5789−ND CONNECTOR HEADER, PCB, HORIZONTAL, 3.5MM, 300V/8A, 5WAY; MC 1,5/5−G−3,5 (1844249);
PHOENIX CONTACT; RoHS=Yes

1

DK:277−2413−ND PLUG SCREW, 3.5MM, 3WAY; MC 1,5/3−ST−3,5; PHOENIX CONTACT; RoHS=Yes

1

DK:277−5721−ND PLUG SCREW, 3.5MM, 5WAY; MC 1,5/5−ST−3,5; PHOENIX CONTACT; RoHS=Yes

1

onsemi P215 ultrasonic ASSP, IO; TSSOP16; NCV75215; onsemi

1

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AND90239/D
APPENDIX 4
Table 5. MASTER BILL OF MATERIALS
Description

Quantity109−7981 SCOPEGND; WIRE BRIDGE, made of 1/36 FCI - 75160−105−36LF - HEADER, 1ROW, 36WAY

1

109−9786 RESISTOR MF_0805_0R_0.1W_100V; WCR0805−R005JI; WELVYN; RoHS=Yes (repl. for 772−239)

8110−0192 RESISTOR MF_1206_1K0_0.25W_1%_200V; WCR 1206 1K 1%; WELWYN; RoHS=Yes (repl. for 420−384)

4

114−6032 USB TO UART; FT232RL; FTDI; RoHS=Yes

1

126−9406 Very low capacitance ESD protection; USBLC6−2SC6; ST Microelectronics; RoHS=Yes

1

128−8255 Capacitor MLC−X7R_0603_100NF_10%_50V; C0603C104K5RAC; KEMET; RoHS=Yes

7

143−1076 DIODE SCHOTTKY 60V/1A; MBRA160TG3; SMA; onsemi; RoHS=Yes

1

146−9752 RESISTOR MF_0603_100R_0.1W_1%_75V; CRCW0603100RFKEA; VISHAY; RoHS=Yes

2

160−7971 SWITCH SPNO 4.5x4.5 mm; 7914G−001−000; BOURNS; RoHs=Yes

1

160−8727 SOCKET, PCB, DC POWER, 2.1MM, 5A, 250V; RAPC722X; SWITCHCRAFT; RoHS=Yes

1

186−5285 HEADER, 1.27MM, Through−hole, 10WAY, 20021111−00010T4LF, AMPHENOL FCI

1

192−4881 LDO, 400MA, 3.3V, NCV4274AST33T3G, SOT223, onsemi

1

192−4884 LDO, 400MA, 5V, NCV4274AST50T3G, TO−252, onsemi

1209−4044 C_MLC−X7R_1206_10UF_10%_25V; 12063C106KAT2A; AVX; RoHS=Yes

2

239−6418 TE−1612618−4; AMP 1612618−4 CONNECTOR, DIMM SOCKET, 200POS; SODIMM200; TE

1

301−9949 Capacitor MLC−X7R_0805_100nF_10%_50V; 2238 580 15649; PHYCOMP; RoHS=Yes

5

499−316

4

Capacitor MLC−NP0_1206_1nF_5%_100V; 12061A102JAT2A; AVX; RoHS=Yes (repl. for 355−4983)

579−0852 LED DIODE GREEN 20mA, 0805; HSMG−C170; AVAGO TECHNOLOGIES; RoHS=Yes

2

855−4501 LED DIODE RED 20mA, 0805; HSMC−C170; AVAGO TECHNOLOGIES; RoHS=Yes

5873−1128 (PK100) TESTPIN 200 SER. HOLE 1.0 BLACK; 20−2137; VERO; RoHS=Yes (repl. for 240−333)

6

923−4489 RESISTOR ARRAY 330R_1206_0.063W_5%; 235003510331; PHYCOMP; RoHS=Yes

1923−8603 RESISTOR MF_0603_10KR_0.1W_1%_50V; RC0603FR−0710KL; PHYCOMP; RoHS=Yes

1

933−1247 RESISTOR MF_0603_4.7KR_0.063W_1%_50V; MC 0.063W 0603 1% 4k7; MULTICOMP; RoHS=Yes

1

933−2391 RESISTOR MF_0805_10K_0.1W_1%_100V; MC 0.1W 0805 1% 10K; MULTICOMP; RoHS=Yes (repl. for 911−975)4

933−2715 RESISTOR MF_0805_1K8_0.1W_1%_100V; MC 0.1W 0805 1% 1K8; MULTICOMP; RoHS=Yes (repl. for 911−884)1

933−3258 RESISTOR MF_0805_470R_0.1W_1%_100V; MC 0.1W 0805 1% 470R; MULTICOMP; RoHS=Yes (repl. for911−811)2

955−6923 DIODE SCHOTTKY 40V/0.5A; MBR0540T1G; onsemi; RoHS=Yes

4

1753806 MINI USB B, RECEPTACLE, SMT, MUSB−05−S−B−SM−A, SAMTEC

1

DK:277−2415−ND CONNECTOR HEADER, PCB, HORIZONTAL, 3.5MM, 300V/8A, 3WAY; MC 1,5/3−G−3,5 (1844223);
PHOENIX CONTACT; RoHS=Yes

4

onsemi DIODE TVS 600W, bidirectional, Vb=28V; 1SMB28AT3G; onsemi; RoHS=Yes

1

onsemi NCV7321; Stand−alone LIN Transceiver, −40.+125C, SOIC8; onsemi

4

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AND90239/D

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