An introduction to electronic weighing

Create your own weighing device with easily available components and open source software.

In this article, I discuss the design of a compact and portable workshop balance for various single-load-cell weighing applications constructed with a small load cell, an instrumentation amplifier, an excitation supply, a microcontroller, a display, and a serial port for debugging. Throughout, I used Linux and open source software, and I provide code samples, with directions for finding the complete code online.

History

Ancient civilizations used simple balances to compare weights for trading in precious metals, spices, salt, and the like. Today’s civilization is no less dependent on knowing the weight of objects. It is hard to imagine a day in which the knowledge of weight does not take part: from the morning visit to the bathroom scales, a trip to the supermarket, baking a cake, to weighing baggage at the airport – the list of times weight plays a part in our lives seems endless. Today, we’ve moved away from mechanical balances, for the most part, obviating the need for ready reference weights.

Today’s weighing equipment is usually based on electronic signals from strain gauges. These sensors are thin-film resistors whose resistance varies in response to tension or compression. When bonded to a mechanical structure subject to the force of an applied mass, the resistance of a strain gauge will change proportionally in response. Practical weighing systems use more than one strain gauge, and these are generally bonded to a metallic billet in a controlled manner to form a more complex electrical circuit designed to eliminate nonlinearities and temperature effects. These billets are known as load cells and are available commercially with working ranges from a few grams to hundreds of tonnes.

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