Скачать презентацию 1975 Capacitive touch switches in use 1994 Скачать презентацию 1975 Capacitive touch switches in use 1994

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1975: Capacitive touch switches in use 1975: Capacitive touch switches in use

1994: 1 st laptop capacitive touchpad 1994: 1 st laptop capacitive touchpad

2003: 1 st i. Pod capacitive touchwheel 2003: 1 st i. Pod capacitive touchwheel

Today: Multi-touch capacitive touch screens How do they work? Today: Multi-touch capacitive touch screens How do they work?

CNMAT Sensor Workshop 2008 Capacitive Touch Sensors 2008 -7 -23 John Lazzaro CS Division, CNMAT Sensor Workshop 2008 Capacitive Touch Sensors 2008 -7 -23 John Lazzaro CS Division, UC Berkeley www. cs. berkeley. edu/~lazzaro CNMAT Sensor Workshop: Capacitive Touch Sensors UC Regents Summer 2008 © UCB

Today’s lecture: Capacitive touch sensing Physics of capacitance Simple touch switches Touch pads and Today’s lecture: Capacitive touch sensing Physics of capacitance Simple touch switches Touch pads and touch screens Novel applications CNMAT Sensor Workshop: Capacitive Touch Sensors UC Regents Summer 2008 © UCB

Physics of Capacitance CNMAT Sensor Workshop: Capacitive Touch Sensors UC Regents Summer 2008 © Physics of Capacitance CNMAT Sensor Workshop: Capacitive Touch Sensors UC Regents Summer 2008 © UCB

Capacitor: A part you buy from Digikey. CNMAT Sensor Workshop: Capacitive Touch Sensors UC Capacitor: A part you buy from Digikey. CNMAT Sensor Workshop: Capacitive Touch Sensors UC Regents Summer 2008 © UCB

Capacitor: Two conductive plates, separated by an insulator (dielectric). Current cannot flow through an Capacitor: Two conductive plates, separated by an insulator (dielectric). Current cannot flow through an insulator. Thus, electrons can’t pass from A to B. CNMAT Sensor Workshop: Capacitive Touch Sensors UC Regents Summer 2008 © UCB

Battery pumps electrons from plate A to plate B. We notate each electron pumped Battery pumps electrons from plate A to plate B. We notate each electron pumped from A as and refer to it as a positive charge. CNMAT Sensor Workshop: Capacitive Touch Sensors UC Regents Summer 2008 © UCB

How many does a 1. 5 V battery place on plate A? It depends How many does a 1. 5 V battery place on plate A? It depends on the 3 -D shape of the capacitor, and the material properties of the dielectric. A: Area of plates d: Plate separation ϵ: Dielectric property Q: Number of V: Voltage on plates CNMAT Sensor Workshop: Capacitive Touch Sensors The ratio Q/V is defined as the capacitance C of the device. Q = CV UC Regents Summer 2008 © UCB

We can use a capacitance meter to measure C. LED Display Conceptually, the meter We can use a capacitance meter to measure C. LED Display Conceptually, the meter puts a V across the C, and then drains off the charge and counts Q. C = Q/V. CNMAT Sensor Workshop: Capacitive Touch Sensors UC Regents Summer 2008 © UCB

Notation alert! From now on we draw net charge on the plates. field lines Notation alert! From now on we draw net charge on the plates. field lines A capacitance meter counts the number of field lines (and thus, Q). CNMAT Sensor Workshop: Capacitive Touch Sensors We draw field lines to illustrate the pairing of charges. UC Regents Summer 2008 © UCB

Simple Touch Switches (Sources: Analog Devices, Cypress, and Synaptics data sheets and websites). CNMAT Simple Touch Switches (Sources: Analog Devices, Cypress, and Synaptics data sheets and websites). CNMAT Sensor Workshop: Capacitive Touch Sensors UC Regents Summer 2008 © UCB

i. Pod 3 G front panel What’s on the back of the PC board? i. Pod 3 G front panel What’s on the back of the PC board? Traces on back of PC board form the “capacitors”! Capacitance meter chip (Synaptics) CNMAT Sensor Workshop: Capacitive Touch Sensors UC Regents Summer 2008 © UCB

PC trace design for a capacitive button switch PC Board Top View Plate A PC trace design for a capacitive button switch PC Board Top View Plate A Plate B What does the finger do? i. Pod White Plastic Casing Capacitor Plate A PC BOARD Cross. Section Capacitor Plate B s ne i dl l fie Copper Glass Copper FR-4 (insulator) field line s Copper FR-4 Copper CNMAT Sensor Workshop: Capacitive Touch Sensors UC Regents Summer 2008 © UCB

Some of the field lines will terminate on the iron in the red blood Some of the field lines will terminate on the iron in the red blood cells of a nearby finger. Recall Capacitance meter counts the number of field lines to determine Q, and then computes C = Q/V Capacitor Plate A CNMAT Sensor Workshop: Capacitive Touch Sensors Capacitor Plate B UC Regents Summer 2008 © UCB

Compact button switch designs Capacitor Plate A LED Capacitor Plate A Capacitor Plate B Compact button switch designs Capacitor Plate A LED Capacitor Plate A Capacitor Plate B dm se sen ly ive t aci ap cha e cal ni itch sw C Capacitor Plate A Capacitor Plate B Capacitor Plate A

Capacitive fader design Capacitor Plate B 0 Plate B 1 Plate B 2 Capacitor Capacitive fader design Capacitor Plate B 0 Plate B 1 Plate B 2 Capacitor Plate A Plate B 3 Plate B 4 Plate B 5 Plate B 6 Super-resolution via interpolation. . . Plate B 7

Touch wheel design B 0 B 1 B 7 B 2 Plate A B Touch wheel design B 0 B 1 B 7 B 2 Plate A B 6 B 3 B 5 B 0 B 4 B 1 B 2 A B 7 B 6 B 3 B 4 B 5

Keypad design A One switch Switch array B 0 B 1 A (connect all Keypad design A One switch Switch array B 0 B 1 A (connect all As together) B 0 B 1 If row I and column J have big Cs, key Kij is touched

Scaling up Scaling up

Typical part $3. 04 Qu 1 $1. 69 Qu 5000 Senses 14 Cs Typical part $3. 04 Qu 1 $1. 69 Qu 5000 Senses 14 Cs

Interesting AD 7142 facts. . . Pad C a few p. F. Finger ΔC Interesting AD 7142 facts. . . Pad C a few p. F. Finger ΔC a few f. F ! Measured pad C is always drifting. Sensor chip tracks it adaptively. Sense time per pad: 3 ms. If all 14 channels in use: 36 ms “frame rate”. Plastic thickness over PCB: 2 -4 mm. CNMAT Sensor Workshop: Capacitive Touch Sensors UC Regents Summer 2008 © UCB

Touchpads and Touchscreens CNMAT Sensor Workshop: Capacitive Touch Sensors (Sources: Apple, Synaptics, and Cirque Touchpads and Touchscreens CNMAT Sensor Workshop: Capacitive Touch Sensors (Sources: Apple, Synaptics, and Cirque patents, UCvarious websites). Regents Summer 2008 © UCB

Touchpad: A circuit board Back view: Capacitance meter chip Top view - finger surface Touchpad: A circuit board Back view: Capacitance meter chip Top view - finger surface

Touchpad Cross-section Grid cross-points are sensor capacitors. Touchpad Cross-section Grid cross-points are sensor capacitors.

Touch screens use a transparent wire matrix (ITO, Indium-Tin Oxide) under glass or plastic. Touch screens use a transparent wire matrix (ITO, Indium-Tin Oxide) under glass or plastic.

The Sensor Array Cross-Point close-up Recall. . . Capacitor Plate B Capacitor Plate A The Sensor Array Cross-Point close-up Recall. . . Capacitor Plate B Capacitor Plate A

Sensor Array Some of the field lines will terminate on the iron in the Sensor Array Some of the field lines will terminate on the iron in the red blood cells of a nearby finger. If many fingers may touch at once (multi-touch), scan out Cij array (frames) at a constant frame rate. “Capacitance video camera”.

Circuit from Apple patent teaching the i. Phone touchscreen controller chip. Like a camera Circuit from Apple patent teaching the i. Phone touchscreen controller chip. Like a camera chip readout Excite one row with a sense waveform Read capacitance of all columns in To parallel A/D channels

One A/D readout channel Not feasible in 1994. . . Looks a lot like One A/D readout channel Not feasible in 1994. . . Looks a lot like a radio receiver. . . Which may be why Apple partnered with Broadcom for the design!

Before Multi-touch Single-touch: A fast accurate keypad Keypad recap: Switch Array B 0 B Before Multi-touch Single-touch: A fast accurate keypad Keypad recap: Switch Array B 0 B 1 adapted the keypad idea to track one finger over a track pad cross-point matrix (1991). Connect all As together One switch If row I and column J have big Cs, key Kij is touched

Before Multi-touch B 0 B 1 First, drive all Y lines simultaneously, and measure Before Multi-touch B 0 B 1 First, drive all Y lines simultaneously, and measure X capacitance vector. . . Then, drive all X lines simultaneously, and measure Y capacitance vector. Track peaks over time, etc. . .

All-analog computation ! Analog background C normalization To identical circuits for Y. Analog peak All-analog computation ! Analog background C normalization To identical circuits for Y. Analog peak interpolation A/D at very end.

For your design: A typical part Most 2 -D products are sold as per-customer For your design: A typical part Most 2 -D products are sold as per-customer custom modules (Synaptics) or done as in-house ASICs (Apple). Recently, standard parts have started to appear. . .

Novel applications CNMAT Sensor Workshop: Capacitive Touch Sensors UC Regents Summer 2008 © UCB Novel applications CNMAT Sensor Workshop: Capacitive Touch Sensors UC Regents Summer 2008 © UCB

Touch sensing ideas. . . Techniques not limited to finger capacitance CNMAT Sensor Workshop: Touch sensing ideas. . . Techniques not limited to finger capacitance CNMAT Sensor Workshop: Capacitive Touch Sensors UC Regents Summer 2008 © UCB

Touch pad and touch screen ideas. . . Techniques are not limited to the Touch pad and touch screen ideas. . . Techniques are not limited to the Cartesian coordinate space. CNMAT Sensor Workshop: Capacitive Touch Sensors UC Regents Summer 2008 © UCB

Touch sensing ideas. . . Techniques can be adapted to flexible printed circuit technologies. Touch sensing ideas. . . Techniques can be adapted to flexible printed circuit technologies. CNMAT Sensor Workshop: Capacitive Touch Sensors UC Regents Summer 2008 © UCB

Touch user interfaces on curved surfaces (Apple patent) Touch user interfaces on curved surfaces (Apple patent)

Touch user interfaces on curved surfaces (Apple patent) Touch user interfaces on curved surfaces (Apple patent)

Final thought Touch Sensing = Materials + Electronics + Product Design A decade ago, Final thought Touch Sensing = Materials + Electronics + Product Design A decade ago, a design team needed experts in all 3 disciplines to succeed. Today, sensor chips and Internet PC board services change the equation. Sensing on curved surfaces await their i. Pod moment -- a product design concept that brings them mainstream.