MacBook trackpad: Accurate enough to be a scale
Apple's solid-state cursor field detects pressure very accurately. This is even enough to determine what you put on it to the nearest gram.
Weighing with a MacBook: Useful and surprisingly accurate.
(Image: Krish Shah/Screenshot)
Apple's trackpad built into the MacBook Pro and MacBook Air has a surprising additional function: the built-in sensors can also be used as scales. Developer Krish Shah has published a corresponding app called TrackWeight on GitHub. The accuracy is in the gram range, sometimes even lower. However, a private API must be accessed for the query.
Solid-state technology with sensors
The trackpads in MacBooks have been using solid-state technology for years: the high-performance cursor control devices are mechanically immobile and detect movement and pressure using integrated sensors. Clicks are simulated by a vibration motor (Tapic Engine). This feels very natural in practice. Funnily enough, the system already provides gram data; the pressure exerted is conveyed internally accordingly.
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Shah uses the OpenMultitouchSupport library from developer Takuto Nakamura to access the data. This makes all the necessary data accessible that Apple does not officially provide. However, measuring a weight is not entirely convenient: the trackpad can only determine the value when a finger (or another object with electrical capacity) is placed on it.
The finger must be in contact; otherwise, it will not be read
This means that you have to place it very gently (virtually floating). In addition, the object to be weighed must be placed in such a way that it does not interfere with the finger contact. After all, metal objects cannot be weighed without problems, as they can be recognized as finger contact. Shah recommends placing a piece of paper or a light cloth in between.
Shah has carried out various calibration processes for TrackWeight, which should ensure an accurate measurement result, as long as the above restrictions are observed. Whether you really want to use a MacBook as a replacement for a kitchen scale is up to each user to decide. However, the app, which is explicitly intended for “experimental and educational purposes” only, shows what is possible with modern sensors. The only pity is that it requires access to private APIs. OpenMultitouchSupport provides lots of exciting information about the trackpad.
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