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
- 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
- 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 (robert.manzke@fh-kiel.de), PCB Design
- Henrik Langer (henrik.langer@student.fh-kiel.de), Component Selection, Driver Development for Beagle Bone Series