Saturday, December 11, 2010

Interfacing TI Launchpad to Digital Caliper

Using msp430 Launchpad to Connect Digital Caliper to RS232 serial port

Caliper and Launchpad
MSP430 Launchpad  from TI is new, very affordable (4.35$), value line development platform. It uses MSP430G2231 - msp430 series mcu and includes everything you'll need to start programming microcontroller. In this article I'll show how to use this development platform to read data from digital caliper and send then to PC RC232 serial port.

You can get digital caliper from from about 7$ with shipping. I bought it from this seller, but you can search for Digital Vernier Caliper to find many more. Most of them have small digital port on side, with 4 pins. You could connect data port to  microcontroller and use digital caliper as precise position sensor, for instance.

Taking it Apart

vernier caliper back, break open
Before connecting wires and reading data I wanted to find out "what's inside" and what principle is used to sense position changes. After some struggle with screwdriver and trying to open it up with force, I discovered there 4 screws on back of main unit with display. You just have to take off plastic sticker from back.

calipers body with pealed off plasticWhat I discovered or maybe more correct to say, proved to myself as I have been reading other articles that was talked about this, was that "capacitance" was used to sense movement. PCB that has display had small strips of copper. Similar pattern is on calipers part that moves, the one with units and digits. Basically both of those parts form series of capacitors and when caliper inside part is moved, all those "capacitors" are changing capacitance and from the sequence in what it changes, MCU inside caliper calculates by how far it has moved.