Introducing the amsO STATIC RAMS Optical Force sensor.

In recent HMI (Human-Machine Interface) designs, there is a demand not only for aesthetic appeal but also for reliable input detection while minimizing errors.
In particular, in automotive, industrial, and home appliance control panels, considerations must be taken into account, such as operation with wet hands or gloves, the use of metal or thick decorative panels, and stable operation in EMI environments. Conventional mechanical SWITCHES and capacitive systems are increasingly finding it difficult to meet all of these requirements simultaneously.
This is where the Optical Force Sensor (OFS) comes into play. OFS uses an optical detection method to detect minute "deflection" of the cover material caused by pressure as a change in light intensity. Because it detects pressure optically, it is less dependent on the presence or absence of conductivity and has the major advantage of being easily applicable to a variety of surface materials, including metals and wood.
This article summarizes the detection principles and design points of OFS (Optical-Free System), and introduces the technical features and use cases of amsO STATIC RAMS 's OFS product, AS7100.

What is OFS?

OFS is an optical sensor that uses infrared light to detect minute deflections (displacements) of objects such as cover materials and measures the amount of change with high precision. The change is so small that it is almost imperceptible to the human eye, but it appears as a difference in the amount of light reflected and returned. OFS converts this difference into an electrical signal to determine whether or not an object has been pressed and how much force has been applied. Because it does not require direct contact with electrodes, it is easy to apply to a variety of cover materials where aesthetics are important, such as metal, resin, glass, and wood.

Basic principles of OFS products

Deflection (displacement) detection using OFS is mainly performed using the following procedure.

amsO STATIC RAMS OFS product: Key features of the AS7100

The AS7100, an OFS (Optical-Free System) product offered by amsO STATIC RAMS, integrates the light-emitting unit, light-receiving unit, drive circuit, and signal processing circuit necessary for OFS implementation into a single package, lowering the barrier to OFS implementation. Because these functions are realized in a small package of 4.0 mm x 3.05 mm x 0.7 mm, multiple units can be used side-by-side even in limited spaces.
Another major feature is its high displacement resolution, thanks to the adoption of a high-resolution ADC. Because it can capture even minute deflections, it becomes easier to design not only for simple on/off detection, but also for distinguishing between lightly touched and firmly pressed states.
For example, it becomes easier to consider multi-stage input that separates soft and hard presses on a single operation surface, or UI designs that switch functions depending on the amount of pressure applied. This is also effective for products where you want to improve usability without increasing the number of buttons.
Furthermore, because it complies with AEC-Q102-003 automotive quality standards, it can be used in automotive applications that require high reliability. Key features are listed below.

• Built-in high-precision 16-bit ADC (maximum 75 dB SNR)
• Displacement resolution up to 1 µm level (resolution varies depending on the material of the cover and the distance from the sensor)
• Built-in LED driver with adjustable current up to 250 mA.
• I2C interface with a maximum frequency of 400 kHz
• Equipped with 256-byte FIFO memory.
• AEC-Q102-003 compliant
• Small package: 4.0 mm x 3.05 mm x 0.7 mm

Anticipated use cases

Steering wheel SWITCHES

Flat operation of home appliances and industrial equipment