CTAG face2|4 Audio Card, based on AD1938 codec

This document includes board information, assembly guidelines, extensions and revision remarks, license and authors information.

Board information

• 4 layer PCB including ground and power plane
• 10mil tracks offering close to 50Ohms impedance
• Part sizes on board are chosen to allow for hand-soldering 0603 as standard size for resistors etc.
• Used http://kicad.org/ for board design
• Board has 3 logical sections
  • Power supply (digital, analog)
    • Includes separate 3.3V digital supply and 3.3V + 5V analog supply
    • Includes boost converter that allows to run board on dual AA battery pack (3V input)
    • Standard input voltage at P201 should be +5V, see assembly options below
  • Codec including reset circuitry and digital I/O
  • Analog I/O
    • We checked several different single supply rail-to-rail OP Amps, where the cheap TLV272 performed pretty well, similar to the LMV722
• Codec and analog section is mainly based on Analog Devices reference design http://www.analog.com/media/en/technical-documentation/user-guides/UG-087.pdf

Assembly

• face2|4 BOM shared at Mouser
  • http://www.mouser.com/tools/projectcartsharing.aspx Access ID: 43007b9807
• Start with assembling the power supply sections
  • Several options for configuration are possible
    • A: Simplest possible, assemble only U203, U204, bypass U201 with JP201, bypass L202 with JP206, bypass L203 with JP207, assemble FB202, place JP204. Input voltage can be anything from 6-9V in this configuration.
    • B: No dedicated 3.3V digital do not assemble U202, assemble FB202, input voltage can be anything 2.4V-5V, boost converter will generate 5.5V for low-noise LDOs
    • C: With dedicated 3.3V digital supply, default in schematic, input voltage should be 5V
  • Check if power supply works by observing the LEDs
• Continue with codec, digital I/O and bias circuitry
  • Assembling only C311, C312 + JP301 is enough, using CM bias for test purposes
  • Test codec with microcontroller system, check at R602 R605 for signal output
• Finally assemble analog section
  • May play around with some different OP amps

Extensions

• Created cape for Beagle Bone Green / Black including digital isolators to reduce noise (BBG-cape)
• Beagle Board X15 break out adapters for Hirose headers

Revisions

• face2|4
  • Rev. A2
    • Fixed polarity bug on IN2 at ADC2RP ADC2RN
    • Known Bugs:
    • none
    • Rev. A has polarity bug on IN2
  • Todos for next Rev.
    • Possibly simplify power supply
    • Remove option to choose bias output from codec --> simplify board
    • Option for balanced inputs
    • Optimize pins on P1001 to improve routing, i.e. less vias on high speed digital lines, preserve impedance
• BBG-cape
  • Rev. A
    • Initial Revision
    • Known Bugs: -
• X15 adaptor
  • Rev. A
    • Initial Revision, thanks to Michael Welling for review

License

This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/4.0/. Anyone re-using this design needs to attribute to authors and http://www.creative-technologies.de website.

Authors

• Robert Manzke ([email protected]), PCB Design
• Henrik Langer ([email protected]), Component Selection, Driver Development for Beagle Bone Series