By Alessandro Vinco & Brian Condell
This fifth blog in the Data Capture blog series looks at micro-speaker amplifiers and how they enhance data scanners' operation in the logistics industry. Barcode scanners and wearable computers provide a variety of sounds to communicate with their operators: for instance, a feedback sound for a barcode correctly read, a different sound for a missed barcode, or even another operator announcing to all colleagues through their portable devices of a new delivery approaching the shipping area of the warehouse.
However, factories and warehouses are busy places. Conveyor belts carry boxes around 24/7, robots and robotic arms perform all sorts of operations, and forklifts transport boxes and pallets everywhere: industrial environments are noisy, and communicating in such locations can at times be very hard.
The ability of such compact devices to mount a powerful and high-quality speaker is key: sounds and communications must be clear and especially loud when delivered in highly noisy environments.
Various types of speakers have been developed and used for many years when the size of both the battery and the chassis of the portable equipment was not considered a primary issue. However, the latest developments in the design of advanced multi-function barcode scanners and mobile computers, and the new trend of wearable computers now require special attention to battery life and the overall size of such end devices. Adding a large and powerful speaker to a wearable device that is smaller than the palm of a hand becomes immediately a tough challenge! See Figure 1 below for a traditional speaker.
Figure 1: Cross-section of a traditional speaker showing the diaphragm, coil, and magnet
New technologies have been brought to market to allow the so-called micro-speakers to replace traditional larger speakers and provide a somewhat comparable level of sound clarity in a much smaller form factor (see Figure 2 below). Mostly driven by the adoption of smartphones, micro-speakers have quickly been designed into automatic data capture devices, too, and quickly replaced older technologies for portable solutions.
Figure 2: Cross-section and exploded view of a micro-speaker
Of course, such small speakers offer a limited range of power that they can deliver, often limited to a few hundred milliwatts or up to 1-2 watts. Thermal management and a bright sound are particularly important when such speakers are pushed near their power ratings but are mounted within a tight enclosure with limited heat sinking capabilities: thermal dissipation (how hot the voice coil can get before melting) is critical; mechanicals stress from the higher power levels can often cause poor sound quality and buzzing.
However, power rating specifications are only important when the speaker’s temperature and excursion cannot be monitored. Analog Devices has delivered industry-leading solutions in the field of smart speakers by delivering a new type of amplifier featuring the patented technology for Dynamic Speaker Management (DSM) – see Figure 3 below.
Figure 3: ADI's DSM technology offers excursion and thermal protection whilst delivering louder and deeper sound
Enter the MAX98390 DSM amplifier which delivers up to 2.5X loudness and deeper bass with Industry-Leading power consumption out of the same micro-speaker. How does ADI achieve this?
ADI’s micro-speaker amplifier uses an integrated DSP to store the speaker’s information on voice coil and DC resistance, and an I/V sense feedback loop on the speaker to monitor diaphragm excursions and thermal limits. Then, it dynamically adjusts the output profile of the speaker to maximize its pressure sound level (PSL) even beyond the rated limits, still without incurring any damage to the device.
Thanks to the integrated boost converter, the micro-speaker can be pushed to its absolute mechanical limits and output power levels, all whilst maintaining industry-leading power consumption.
The I/V sense loop allows full control of the micro-speaker even when pushed to the maximum thermal limits: sounds are louder and clearer when driven by the MAX98390 amplifier, yet the speaker never exceeds the recommended thermal specifications.
The DSM amplifier uses dynamic and adaptive filters to control the volume level and the speaker’s response at that specific level when compared to a static filter: lower frequency sounds are perfectly balanced while unwanted sounds like rattling and buzzing of the micro speaker inside the enclosure are eliminated.
Analog Devices DSM smart amplifiers use current and voltage (I/V) feedback and integrate a patented DSM speaker protection algorithm within a fixed DSP function. The patented DSM algorithm and I/V feedback enable DSM smart amplifiers to push maximum loudness and bass response without exceeding the micro speaker’s excursion or thermal limits. Communications between warehouse workers and feedback sounds are now clearer than ever with a sound that will also preserve your equipment and your battery life.
