How to Make a Digital Readout for Your Faceting Machine

(Editor's Note: This is a first in a series of articles. Future articles will apply to specific machines, where this first one is general.)

Design principle.

A Digital Panel Meter (DPM) can measure angles to 0.01 degree if a precision instrument potentiometer is used and a stable reference voltage is used. This later version has much lower power consumption that the prior LED model, and can be run from batteries.

Principal of Operation

A trimpot and a sensing potentiometer form a simple voltage divider. Designing for 200 degrees of rotation, each degree equals one millivolt. In actual use, the critical measuring is done at that rotational quadrant from 0 to 90o, or from the Table to Girdle settings. Thus, if the pot is linear to 0.5% over its range, only one quarter of its range is really used. If batteries are used, rather than regulated power supplies, it only takes a minute to check the calibration once in a while. Lithium batteries seem to last forever in this application. The voltage divider only consumes 0.1 milliamp.

Resolution:

0.01 Degree

Linearity error:

Less than 0.125% from zero to 90 degrees.

Cost to build:

Less than $50.

There is a critical

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Jon Rolfe

Jon Rolfe is the president of Gearloose Lapidary, LLC -- an innovation leader in lapidary technology. Find him at gearloose.com.

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