F EATURE
ARTICLE
by Coleton Denninger and Jeremy Lichtenfeld (Canada)
Capacitive-Touch Gain-Controlled Personal Amplifier Two Camosun College graduates designed an inexpensive do-it-yourself personal audio amplifier. The design features capacitive sensing, digital-signal mixing, and high-quality sound.
April 2012 – Issue 261
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hen did you stop thinking about how consumer electronics looked on the outside and ask yourself what happens on the inside? For many consumers, unfortunately, this epiphany will never take place. Most people will live their lives buying, using, and disposing of electronics without ever knowing how they actually work. But for some, this will happen naturally and their curiosity will give them the energy to explore to their hearts’ content. We intend to engage and inspire these inquisitive-minded tech enthusiasts. While studying at Camosun College in Canada, we were tasked with creating a “no-experience-needed” electronics kit that would appeal to middle/high school students. The students would be given a crash course in soldering, so we had to make it as solder-friendly as possible. For this reason, we weren’t allowed to use surface-mount components. We could only use through-hole components. This was because the last thing we needed was a bunch of eighth graders, buzzing on sugar, armed with heat guns! The kit also needed to be sleek
and modern to get kids excited to build it, but without being too expensive or time consuming. Since every kid and his dog owns an iPod, MP3 player, or some other type of personal audio device, it made sense to build a personal audio amplifier (see Photo 1). The tough choices were how we were going to make it stand out enough to attract kids who already own high-end electronics and how we were going to do it with a budget of around $40.
SHOW ME THE PARTS Our first concern was how we were going to mix and amplify the
a)
low-power audio input signals from iPods, microphones, and electric guitars. We decided to have a couple of different inputs, and we wanted stereo and mono outputs. After doing some extensive research, we chose the Cypress Semiconductor CY8C29466-24PXI programmable system-on-chip (PSoC). This enabled us to digitally mix and vary the lowpower amplification using the programmable gain amplifiers and switched capacitor blocks. It also came in a convenient 28-pin DIP package that followed our design guidelines. Not only was it perfect for our design, but the product and
b)
Photo 1a—This is the capacitive-touch stage of the personal audio amplifier. b—Here you see the power-amplification stage of the personal audio amplifier. CIRCUIT CELLAR®
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www.circuitcellar.com
