Lab Notes: 21/08/18

Voice Recorder Module Schematic from the Manual

In pursuit of my goal of creating custom parts to use in Eagle, I stumbled across a three-part tutorial series published by Autodesk. This tutorial series details how to create, packages and symbols, and how to link the two together in a device. I soon discovered that a package is the physical layout of a component and that a symbol is the visual representation of the component in the schematic. These elements are contained within the following hierarchy.

  • Library
    • Device
      • Package
      • Symbol

It didn’t take long to skim read the tutorials and extract the information I needed to design two parts for the low-cost sampler: an electret condenser capsule and a PCB mounted speaker, as shown in the mages below. I found these parts on the wholesale retail site www.alibaba.com. I haven’t ordered through this site before. I assume that many of the low-cost components available through Amazon originate from the same factories in China. Usefully, package dimension details were available directly on the product page of each.

Electret and speaker symbol    Electret and speaker package

Following the creation of these devices in Eagle, I proceeded to breadboard a simplified version of the low-cost sampler circuit. This simplified version was essentially, this schematic minus the line level inputs and outputs and pitch control.  Unfortunately I was still experiencing very low-quality audio. I decided to breadboard a schematic detailed in the user manual provided for the prefabricated voice recorder module board (see the main image at the beginning of this post). Initially, this didn’t work as expected either but did appear to be recording higher quality audio. Almost by accident, I discovered that connecting the REDLED pin to GND improved the quality of audio. Of course I couldn’t leave this connected as it resulted in the Record LED lighting at all times, making it somewhat redundant. However, connecting the Feed-Through pin to GND instead, whereas it was previously floating, solved the audio quality issue and allowed the Record LED to resume its regular function.

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