The three-letter acronym (TLA) for Touch Sensor Module.
The area (width and height / columns and rows) the TSM will scan for an object with lasers and photodiodes (PD). The scanning width is set to the physical length of the TSM, and the scanning range (height) is set by default to ~90% of the width for the majority of the TSM. The scanning range (height) can be changed from the firmware NTSMF 2.0
The area where an object of a specific size, shape and physical properties can be detected.
Depending on the size, shape and physical properties, the detection area can vary on the same TSM size.
Touch Active Area (TAA)
This is the selected (configured) sub area of the scanning area that the TSM will report touches from.
Normal and Extended Range
The default scanning range is sometime referred as "normal range" for some TSM sizes (295, 310 , 346 & 374) the default scanning range is set to 208.5 mm and can be "extended".
The TSM is designed to detect fingers. When measuring the accuracy of the TSM or doing automated test, we need a test object, a finger equivalence. For testing we use a 16mm silicon rod (cylinder), with flat tip to simulate a finger.
Center of (test) object
The TSM can only "see" one side of an object. The width of the object can be calculated from the number of lasers that illuminates the object. The depth of the object is a combination of the curvature, shape, angle and reflectance of the object. The reported touch x-position is the center point of the object and about 3.6 mm from the edge in y direction. This corresponds well to the perceived "center" of a touch when a finger touches a display/screen (I.e. the touch is in the middle of the fingertip).
Test Object Size (and shape)
The TSM can detect small objects. Due to the pitch (distance between the lasers) on the TSM, small object can be placed between two lasers and not get illuminated. This resulting of a missing touch.
If the object is small is will also be harder to detect far away from the sensor due to the signal-to-noise ratio.
The accuracy is connected to the size, shape and reflectance of the object. The accuracy for a TSM is therefor for a specific object size (and shape).
The purpose of the TSM is to report the position of a physical object when it is completely inside the Touch Active Area.
The accuracy is the difference between the reported and the physical position of the object (finger) in front of the TSM.
When a user moves a finger in a line or circle in front of the TSM, the user "wants" the line to be straight and the circle to be round, even if the user doesn't technically draw the finger in a straight line or in a perfect circle.
It is possible to add filters to "enhance" the experience by straightening the drawn line and improving the curvature of a circle. This will increase the "perceived accuracy".
Note: Not all TSMs will have this type of filters and some parts of this is in the base algorithms of the TSM.
Neonode TSM Accuracy Specification
The specification for the TSM is for a specified TSM type, size and configuration. The accuracy is measured with many of the filters turned off to get a "raw optical mechanical accuracy". This enables us to measure the accuracy, accurately and with high repeatability.
When moving an object in a straight line in front of the TSM, the fluctuations (deviation) from that line can be described as a measurement of linearity.
Floating and Floating Protection.
The TSM uses lasers to illuminate an object and calculate the position. For a "touch on surface" system the distance from the surface and the laser beams can described as "floating". If the laser beams are not perpendicular to the surface, the "floating" can be different over the Touch Active Area. When this happens, the time between the tactile feedback from the finger hitting the surface and the reported "touch" by the host (and TSM) will differ over the TAA. This can be described as a latency problem and the system feel inconsistent over the TAA.
With higher floating the shape (curvature) of the finger tip can affect the movement of the touch. I.e. the TSM will "see" the tip of the finger first and then the side of the finger resulting in a movement. Floating protection is a filter which mitigates this problem. The filter gives a "stable" touch event with high floating.
Scanning (finger) frequency and reported (continuous) frequency
Scanning frequency set on the TSM is the speed (frequency) the TSM scans the scanning area. Reporting frequency is the speed (frequency) the host system will receive reported touches.
The goal is that the reported frequency is as high as the scanning frequency. Depending on communication type, protocol and host configuration, the reported frequency can in some cases be lower then the scanning frequency.
Persistent parameters vs runtime configuration
The TSM has two types of configurations, startup and runtime. (persistent parameters and runtime configuration).
The persistent parameters are set when firmware is flashed to the TSM and can be modified using the zForce Programmer tool.
The persistent parameters are loaded during startup and a subset of the parameters can be change during runtime using ASN.1. This is the runtime configuration.