Using this scheme (a bit less compact than the straight binary representation), each decimal digit is represented using a nibble (4-bit). On a side note, BCD stands for “Binary Coded Decimal”. The other two communication protocols are both for the Chinese calipers – “Chinese BCD” and “Chinese Binary” (the suffixes come from the way that the data are being transmitted). The first one is the “Digimatic” from Mitutoyo. You could connect the data output port to a microcontroller and use the digital caliper as position sensor, for instance.Īs I read, there’re basically three types of protocols for interfacing them. The data output port is in fact a communication port for interfacing the digital caliper with a computer or other supported electronics. As observed, the caliper’s circuitry never fully switches off, actually only the LCD that turns off, leaving the LR44 draining 24×7 (that’s why the battery dies quickly).ĭata Output Port & Communication Protocols If you measure the current consumption, you will find that the circuitry draws a lot of current even in the power off state. The caliper uses a 1.5V coin cell – LR44, but the battery lifetime is shockingly short. This is an old patent that describes this technique (translation required) Battery & Power Consumptionīelow is a close up of the circuit board. The term “emitters” in the description above intrigued me, so I did a thorough search and quickly found that they’re actually “exciters” creating a multi-phase pulse width modulated signal capacitively coupled to the ground frame (not yet fully confirmed). The signal processing circuit built into the slider counts the grids as the slider moves and does a linear interpolation based on the magnitudes of the capacitors to find the precise position of the slider”. As the slider moves the capacitance changes in a linear fashion and in a repeating pattern. The combination of these printed circuit boards forms two variable Capacitors. In the slider another printed circuit board contains a set of etched separate grids which are called emitters. A pattern of grids is etched directly on the top copper layer of a standard glass-epoxy laminate of the printed circuit board stator. The set of grid-capacitances consist of stator grid-capacitance and sliding grid-capacitance. “Digital calipers contain Grid-Capacitance Linear Synchronous Sensors which are comprised of a set of grid-capacitances and signal processing circuit. Capacitive Sensing System – Chinese ExplanationĪfter some Googling, I found a sensible custom description of how this type of digital caliper works.
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