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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 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


  • face2|4 BOM shared at Mouser
  • 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


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


  • 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


This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. To view a copy of this license, visit Anyone re-using this design needs to attribute to authors and website.



AD1938-based audio codec PCB






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