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3.3.2 ABS Gain Corrected

The ABS force response shows the different sensitivities of the buttons. Even though they were designed the
same, the mechanical function is different in each case due to variance in the 3D printing. To achieve a more
even response, a gain can be applied to each channel. After applying individual gains, the force response can
be seen in

Sample

Chang

e

in Data Code

0

500 1000 1500 2000 2500 3000 3500 4000 4500 5000

-2000

0

2000

4000

6000

8000

10000

12000

2N

4N

6N

8N

10N

Ch 0
Ch 1
Ch 2
Ch 3

Sample

Chang

e

in Data Code

0

500 1000 1500 2000 2500 3000 3500 4000 4500 5000

-2500

0

2500

5000

7500

10000

12500

15000

17500

2N

4N

6N

8N

10N

Ch 0
Ch 1
Ch 2
Ch 3

(a) Left Side

(b) Right Side

Figure 3-4. ABS Gain Corrected

3.3.3 Nylon Force Response

Similarly, the Nylon 12 force response is gathered and compared.

Table 3-2.

Sample

Chang

e

in Data Code

0

500 1000 1500 2000 2500 3000 3500 4000 4500 5000

-2500

0

2500

5000

7500

10000

12500

15000

2N

4N

6N

8N

10N

Ch 0
Ch 1
Ch 2
Ch 3

(a) Left Side

(b) Right Side

Figure 3-5. Nylon Force Response

Hardware, Software, Testing Requirements, and Test Results

14

Inductive Touch and Magnetic Dial Contactless User Interface Reference
Design

TIDUC26 – APRIL 2022

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Copyright © 2022 Texas Instruments Incorporated

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Summary of Contents for LDC3114-Q1

Page 1: ...like dirt or damages to the button surface The hall sensor dial creates a contact less rotation that has improved wear and tear over traditional contact based implementations such as potentiometers or rotary encoders Resources TIDA 060039 Design Folder SCB Design Folder LDC3114 Q1 TMAG5273 DRV2605 Product Folder TLV755P TCA9534 PCA9543A Product Folder Ask our TI E2E support experts Features Seamle...

Page 2: ...h buttons In this reference design inductive sensing is used to implement seamless touch buttons that provide a contact free implementation while also enabling variable force touch functionality Additionally hall effect sensing is used to implement a contactless dial to reduce the wear and tear that comes with devices like potentiometers and rotary encoders This design includes a 3D printed housin...

Page 3: ...t inductive touch buttons and a magnetic push dial The touch buttons have three different modes of operation that can be changed by pressing in the dial In the default mode the buttons will give a digital output on the LEDs corresponding to which button was pressed In the second mode the LEDs will showcase how hard any given button is pressed by lighting up more LEDs for a harder press The third m...

Page 4: ...e coil diameter becomes a critical design parameter as well Many times this parameter is constrained by the space available for the sensor coils to be implemented on a PCB From there other factors like the number of turns trace width trace spacing and number of layers all account for the overall coil design The trace width and spacing can be limited by the PCB manufacturing process but can also be...

Page 5: ...t RP 3 19 kΩ Q factor Q 37 00 Self resonant frequency estimated SRF 62 831 MHz Target Distance D 0 800 mm Sensor Inductance from Target Interaction L 0 921 µH Sensor Frequency with Target Interaction fRES 11 081 MHz RP with Target Interaction RP 1 68 kΩ Q Factor with target Q 26 0 Since the button surface is 3D printed it also includes the required spacer for the button design instead of having a ...

Page 6: ...Conductive Rigid Surface Conductive Target Force Stiffener Optional Figure 2 4 Non Conductive Touch Button Alternative Stackup Example 2 2 2 Sensor Coil Placement The LDC3114 allows for sensor coils to be placed remotely rather than next to the IC due to the addition of the COM pin and placing the sensor capacitor near the device instead of next to the coil This provides a better EMI response for ...

Page 7: ...ll scale output range This provides a better SNR performance for the device when used at a suitable distance for the design while still being small and it is easy to obtain Distance mm Mag_B mTesla 0 0 4 0 8 1 2 1 6 2 2 4 2 8 3 2 3 6 4 4 4 4 8 5 2 5 6 6 6 4 6 8 7 2 7 6 8 0 15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 Figure 2 5 Magnetic Field Strength Over Distance The push functionality ...

Page 8: ...atically correct for any deformation in the conductive targets The LDC3114 Q1 offers well matched channels which allow for differential and radiometric measurements which enable compensation of environmental and aging conditions such as temperature and mechanical drift The LDC3114 Q1 includes an ultra low power mode intended for power on off buttons or position sensors in battery powered applicati...

Page 9: ...ate This reference design uses the 1 8 V output option of this device to supply power to the LDC3114 devices and level shifters 2 3 5 TCA9534 The TCA9534 is a 16 pin device that provides 8 bits of general purpose parallel input and output I O expansion for the two line bidirectional I 2C bus or SMBus protocol The device can operate with a power supply voltage ranging from 1 65 V to 5 5 V which all...

Page 10: ...rding to the coil design discussed above The DRV2605 haptic driver is setup to perform haptic feedback when and I2C command is received The device is also setup for the specific LRA that is attached to the board and runs a calibration check each initialization The TMAG5273 is setup so that the X and Y components of the magnetic field are used for rotational calculations This device can also be con...

Page 11: ... 1 Get Hall Angle and Magnetude Update Circle LEDs Hall mag above threshold Op Mode 1 Change in Button Status Haptic FB Collect Data for GUI Yes 1 2 3 No No Yes No No Yes Yes No Yes Yes No No Yes No Figure 3 2 Operational Modes Flowchart During normal operation this reference design has three different operational modes that change the functions of the inductive touch buttons www ti com Hardware S...

Page 12: ...rent This mode looks at the data value from the baseline tracking algorithm on all buttons and determines which button has the highest force press From there LEDs are lit up depending on how hard the button is pressed with more force turning on more LEDs Each time this mode is entered a max force is reset to a standard value If a button is pressed hard enough a new maximum force value will be save...

Page 13: ...tely uniform or have design tolerances large enough to impact the performance Additionally testing with two different materials shows the differences between them as well Table 3 1 Button Press Force Required Button Position ABS Left Newtons ABS Right Newtons Nylon Left Newtons Nylon Right Newtons 1 7 5 2 3 75 2 20 3 5 3 0 75 3 16 1 5 1 1 5 4 3 1 3 1 3 3 1 ABS Force Response The differences shown ...

Page 14: ...a Code 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 2500 0 2500 5000 7500 10000 12500 15000 17500 2N 4N 6N 8N 10N Ch 0 Ch 1 Ch 2 Ch 3 a Left Side b Right Side Figure 3 4 ABS Gain Corrected 3 3 3 Nylon Force Response Similarly the Nylon 12 force response is gathered and compared Table 3 2 Sample Change in Data Code 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 2500 0 2500 5000 7500 10000...

Page 15: ...ince the data moves in the opposite direction from the button press the impact can be ignored in the application and the baseline algorithm in the device has additional tools to handle this impact so that it does not become an issue That being said cases like this can be minimized by isolating the mechanical movement as best as possible Lastly after gain correction on both materials the difference...

Page 16: ...B The top cover is broken into multiple parts to make it easier to print with some 3D printing technologies These different parts are the button surface a dial attachment the dial and a small cover for the top portion of the PCB The button surface has grooves on the top to show where a button press should occur and a hole in the middle for the dial attachment piece to sit in On the back there are ...

Page 17: ...n Figure 4 4 Button Cover with Dial Attachment The dial is designed to clip onto the dial attachment with a spring sitting between the two The dial also has a small hole that the magnet gets glued into This allows for the magnet to sit directly above the TMAG5273 for best rotational sensing measurements www ti com Hardware Components TIDUC26 APRIL 2022 Submit Document Feedback Inductive Touch and ...

Page 18: ...USB cable to connect to the SCB The main purpose of the top cover is to complete the housing and hold the SCB in place Figure 4 6 Full Assembly Hardware Components www ti com 18 Inductive Touch and Magnetic Dial Contactless User Interface Reference Design TIDUC26 APRIL 2022 Submit Document Feedback Copyright 2022 Texas Instruments Incorporated ...

Page 19: ...orithm Functionality application note 4 Texas Instruments Inductive Touch Configuring LDC2114 and LDC3114 Touch Button Sensitivity application report 5 4 Support Resources TI E2E support forums are an engineer s go to source for fast verified answers and design help straight from the experts Search existing answers or ask your own question to get the quick design help you need Linked content is pr...

Page 20: ...o change without notice TI grants you permission to use these resources only for development of an application that uses the TI products described in the resource Other reproduction and display of these resources is prohibited No license is granted to any other TI intellectual property right or to any third party intellectual property right TI disclaims responsibility for and you will fully indemn...

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