A smart fluid level instrument in a sports drink bottle

Students in a mechanical engineering program are given the task of converting parts from a sports drink bottle into a capacitive fluid level probe. The project begins in a third-year instrumentation course when student teams develop a prototype instrument design. During a subsequent computer data acquisition and control course, the students use their prototype with the addition of an embedded processor (microcontroller) to create a "smart" instrument. The students are given loose specifications for the design of their fluid level probe. The specifications have enough freedom to allow for creative variation in designs but key factors are tightly defined such that the performance of all of the designs can be compared. The students must then develop a detailed written specification for the prototype that they actually produce. A popular sports drink bottle is used as the envelope into which the design must fit. The lid of the bottle serves as the bulkhead for the probe and all required electronics. The bottle itself serves as a protective case for transport of the probe and a containment vessel for any residual fluid present after testing the probe in the test chamber. Lightweight mineral oil is used as the measurement fluid due to its desirable electrical properties and its odorless and non-flammable characteristics. This paper presents and discusses the details of the prototype development from specification writing to prototype testing. Student-developed software is also presented and discussed. Project objectives and course outcomes are also presented.