Touchscreen Technologies: Ultrasonic, Near Field, and Standards
Touchscreen Technologies and Display Standards
Ultrasonic Touchscreen Technology
Used technology: Ultrasonic transducers generate surface waves transmitted through the glass surface and received by sensors on the opposite side. A pointer touching the screen absorbs some acoustic wave energy. The receiver measures changes in the received acoustic wave’s amplitude to detect the pointer’s position.
Advantages
- Total light transmission
- Protection through a graphical display
- Ability to detect the depth of the touch
Disadvantages
- Requires a push pointer to absorb acoustic wave energy
- Susceptible to noise and interference
- Difficult to industrialize production
- High consumption
- Sound waves are affected by liquids or contaminants on the screen
Near Field Imaging Technology
Technology used: Robust and perfect for harsh industrial environments. Uses two glass sheets separated by a transparent metal oxide layer. Applying AC to the metal oxide creates an electrostatic field on the screen’s surface. A pointer touching the screen disturbs this field.
Advantages
- Good light transmission
- Extremely robust
- Works with a finger or conductor
- Good accuracy
Disadvantages
- High cost
Graphic Display Management Standards
1. Video Standards
TTL (Transistor-Transistor Logic)
- Digital video graphic displays used in LCDs
- Parallel data transfer through a flat cable
- Can work at 5V or 3.3V
LVDS (Low-Voltage Differential Signaling)
- Digital video LCD graphic displays used in large screens
- Known as FPD-Link (Flat Panel Display Link)
- Data transmission through a twisted-pair cable
- Can use one or two channels in parallel
- Can work at 5V or 3.3V
DVI (Digital Visual Interface)
- Digital flat panel displays for high-end personal computers
- Combines digital video and video input: DVI-A, DVI-D, DVI-I
- Uses one or two-channel TMDS (Transition Minimized Differential Signaling) format
2. LCD Backlight
LCD Backlight: Used in LCD displays. The light source is usually one or two white fluorescent tubes with a diffuser that evenly distributes light across the screen. The diffuser is typically a plastic lens with aluminum foil acting as a mirror, reflecting light outward. A high-voltage AC is needed to power the fluorescent tubes, generated by an inverter (DC-AC).
Registered Potentiometers
This may refer to a closed-loop recorder or servorecorder. The pen’s position is controlled by a cursor moving along a linear potentiometer. The cursor’s position determines the potential applied to an operational amplifier, which subtracts the signal for measuring the signal coming from the transducer. The amplifier output is related to the difference between the pen and transducer signals. This signal drives a servomotor, controlling the pen’s movement on the chart. The pen moves to a position where there is no difference between the pen and transducer signals.
They have high input resistances and accuracies higher than galvanometer recorders, but slower response time.