Publication date: 27 April 2010
Training and exercise equipment is a highly fashion conscious industry, and even POWERbreathe, a respiratory exercise system design recognised by the Design Council in 2001, needed to evolve to meet the needs and expectations of its users. Manufacturers HaB International recognised the need to offer users new levels of information, control and usability, which entailed adding electronics. At the same time, they recognised that the equipment will end up in a corner gathering dust if the batteries don’t last. Electronic product design specialists ML Electronics were given the challenge of creating an electronic design that met users’ expectations fully, but could comfortably run from rechargeable NiMH AAA batteries – including driving a 12V stepper motor.
POWERbreathe is a hand-held Inspiratory Muscle Trainer, a multifunctional training tool for lung function, providing a wide variety of applications for a broad range of people, from athletes to patients with respiratory problems such as chronic obstructive pulmonary disease and asthma. Using resistance training, similar to using weights and pulleys to hone muscles such as arms or legs, the POWERbreathe concept was initially developed in 2001 based on mechanical pressure threshold training using a load calibrated spring. The original POWERbreathe Classic series was named a Millennium Product by the UK Design Council.
In developing the third generation POWERbreathe Kinetic, manufacturers HaB International needed to respond to the needs of the iPod generation of users, and offer users more control over their exercise regime and be able to provide more information on their exercise progress, which entailed introducing an LCD display and microcontroller. New features on the POWERbreathe Kinetic series include an electronically controlled, rapid-response valve to create a resistance to inhalation. Training resistance matches the dynamic changes in breathing muscle strength throughout the breath and then automatically adapts to increases in inspiratory muscle strength at the start of each training session. Training measurement results are displayed on an LCD screen, allowing quick and easy monitoring of training progress and optimisation of training technique. An LCD menu system allows users to navigate between different settings and to view training results.
Working closely with HaB’s product and design innovation specialists, Smallfry, the key challenge for ML Electronics was to achieve the very low power consumption in a small form factor envisaged by Smallfry’s concept design, whilst ensuring the bill of materials and manufacturing costs were kept to a minimum so that the product remains affordable. Foremost in the brief was the specification that POWERbreathe should run from a maximum of three NiMh cells and be recharged via a 5V supply from the USB port. Batteries were required to last two weeks on a full charge, enabling the user to follow a training programme of 30 breathe-in/breathe-out cycles, twice a day. Despite this constraint, the design needed to drive a 12V stepper motor, which controls the valve that provides different levels of breathing resistance via a variable diameter orifice.
This limited power budget, space constraints and available bill of materials eliminated the possibility of fast charging, so advanced power management techniques and power efficient circuit design were used for optimising the power consumption.
The heart of the POWERbreathe electronics is a PIC microcontroller. This takes values from a pressure sensor and uses them to control the stepper motor, ensuring that the ‘resistance’ is constant throughout the breath. Motor performance and control speed were critical in order to ensure sufficiently fast feedback. HaB’s patented Auto-Optimising IMT Technology automatically selects the most effective training load, based on respiratory muscle strength. Training results, progress and physiological respiratory measurements are continuously monitored and displayed on the high contrast LCD display. Better still, the user’s performance and progress can be analysed on a PC through the device’s USB connection.ML Electronics used many features available in the Microchip processor such as, micro-Amp real-time clocks, low power system voltage monitors, and the ability to run the CPU core at a different speed from the peripherals.
Functional circuitry was completed with differential amplifiers to provide inputs from the breath pressure sensor and a stepper motor driver linked to a low-cost off-the-shelf motor. In addition, the design provides a buzzer (the POWERbreathe uses sound to tell users when to start and stop), LED and LCD displays, a function button and USB2.0 interface. All circuits can be switched in and out to conserve power using software developed by HaB themselves.
More crucially, the hardware design needed to minimise voltage drops everywhere. This not only impacted on the tracking and layout, but also necessitated using FETs instead of standard diodes which resulted in a very compact printed circuit board. A key design aspect to the printed circuit layout was the power consumption caused by any voltage-drop along the length of the copper tracks. Even a 0.1V drop can translate to a significant lowering of battery life.
POWERbreathe Kinetic is currently going into volume production. It is expected to be available in time for Christmas; and for the New Year health and fitness peak.
