Electronic Stethoscopes Project

Starting Date

09/01/2006

Completion Date

02/15/2007

Objective

Each student will construct a working electronic stethoscope using fundamental electronic components such as resistors, capacitors, diodes, and operational amplifiers.

Unique Approach

We are not just doing a project; we are developing a useful product. This provides an opportunity for students to find out what really motivates good engineers: the thrill of creating something that other people will be excited about and want to use.

In a traditional classroom setting, students are frequently asked to learn difficult concepts without knowing how those concepts might be useful in real life. Unlike the traditional classroom, our workshops do not treat learning as an end unto itself. By focusing on a product and its end-user applications, we are placing learning into its proper context as something that will enable the student to better serve the needs of other people in society. We are helping the student to build a bridge between their schooling and their career.

Strategy

Each club member will construct a working electronic stethoscope. The circuit uses a dual TL072 op-amp and is powered by two 9v batteries. It includes a low-pass filter and adjustable gain.

A microphone jack will allow the students to use a variety of microphones for specialized applications:

• Medical stethoscope – Each student will mount a tiny condenser microphone inside a stethoscope chestpiece for listening to heart, breath, and bowel sounds of people and pets.
• High gain listening device – Each student will receive an additional condenser microphone that they can use to pick up faint sounds such as the ringing of a pin that is dropped onto a hard surface or the sounds emitted by insects.
• Mechanic’s stethoscope – Students who are interested in auto mechanics can attach a microphone to a sounding rod in order to listen to engine noises.
• Directional microphone – One microphone will be mounted in parabolic reflector and remain property of the club. Students can borrow this high gain directional microphone and use it with their amplifier units to listen to bird sounds or distant conversations.

We will be injecting healthy doses of theory along the way so that the students understand the purpose of each component and how the components interact within the circuit. Students will be encouraged to think about ways to customize their products for specialized purposes.

Sequencing

The project will be accomplished in five stages:

• Stage 1 – Breadboarding – Each student will construct a working stethoscope using a solderless breadboard.
• Stage 2 – PC Board Construction – Each student will lay out and etch a PC board and then solder the components onto the board.
• Stage 3 – Product Realization – Each student will mount the PC board in an enclosure which will also house the two 9-volt batteries. They will create a front panel that includes a power switch, a low-pass filter on/off switch, a volume control, a microphone jack, and a headphone jack.
  
  In order to be commercially successful, a product must appeal to consumers. This requires the designer to pay attention to issues such as flexibility, ease of use, and durability. The key concepts being learned here are “modularity”, “encapsulation”, and “interfaces”. Everything inside the enclosure is hidden from the user. Anything that passes through a hole in the box is either an input or an output. This is a chance to relate these concepts to integrated circuits (IC’s), showing how modularity and interfaces can exist at multiple levels, allowing greater levels of complexity to be achieved by making things at lower levels look like black boxes.
• Stage 4 – Usability Testing – Each student will be encouraged to take their completed device home and use it to explore the sounds in their environment such as their pet’s heartbeat or (with supervision) the bearing noise in a noisy car alternator. We will subsequently meet and discuss each student’s experiences with an emphasis on uncovering weaknesses in the design or possibilities for future enhancements. We will ask “What would it take to make this a commercially successful product?”.
• Stage 5 – Continuing Education – We will subscribe to two project-oriented electronics magazines that will be made available to students who wish to continue learning about electronics after the project has concluded.

Mentors

To reinforce our emphasis on products and end-users, we are planning to invite two guest speakers: an emergency room doctor who can show the students how to use their stethoscopes to auscultate heart, breath, and bowel sounds, and a mechanical engineer who leads an engineering team that designs medical ultrasound transducers. Both of these young professionals are recent graduates of our high school.