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Return to BlogRS232 Input Interface for Digital Caliper
Posted Jan 25, 2012 at 11:35 am
Figure 1
An electronic digital caliper is made to record the measurements to a computer with the use of RS232 interface.
The design of the device can work not only with inexpensive calipers but also with height gauges and micrometers. The connector has 4 pins on the measuring instrument with 90 kHz 24-bit synchronous outputs.
A burst of data is being sent by the caliper at around 3 times each second where 48 bits of data are contained in each burst. The position relative to the zero point set on the caliper refers to the first 24 bits while the second 24 bits is referred to a fixed arbitrary zero. The ones compliment value is the form used by each 24 bit value. Only when the caliper loses power will the zero point change.
A small 1.5V battery can normally power the caliper with the metal parts of the caliper connected to the positive of the battery to make it positive ground. The burst of data from the caliper is being handled by the synchronous receiver from the microcontroller firmware. Data from both the PC and caliper is checked by the interface while idle.
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2 years ago: for high school use, this is not yet suitable because the students will not learn the way to use a calipher manaually. but for professional use, this is recommended in order to obtain the precise measurement.