CSR8645 Bluetooth 4.0 AAC APT-X Module / Baseboard - diyAudio
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Old 26th January 2016, 01:39 AM   #1
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Default CSR8645 Bluetooth 4.0 AAC APT-X Module / Baseboard

To my knowledge and what i have had read here in the past, there's always some trouble with those "chinese" bluetooth modules. (Noise, Performance, Range, etc.)

So i'll make "my own" baseboard for the CSR8645 modules.

The modules i use are available here:

2015 New CSR8645 4.0 Low Power Consumption Bluetooth Stereo Audio Module Supports APTx-in Other Electronic Components from Electronic Components & Supplies on Aliexpress.com | Alibaba Group

The board will nothing to fancy.

- dual power input (USB / DC-IN 6-15V)
- differential output or diff2se stage
- MKS/MKT coupling caps for those who need.
- break-away with buttons
- all GPIO on pinheader
- SPI interface (maybe with 3V3 levelshifter)
- output on pinheader or 3.5mm jack
- 3.5mm input jack with "priority" routing
- 50x50mm pcb space using standard components
- easy to solder due to 0603 parts (some 0402 ferrites at the USB line)

Well, thats it. I want to use this for small class-d-amps (TPA3116/3118/3251/3250 etc.)

Actually arranging parts..

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Old 26th January 2016, 02:10 AM   #2
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Any chance of an I2S output?
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Old 26th January 2016, 02:57 AM   #3
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This might be a silly question but would isolating the power input on this board be helpful? I know quite a few people power their small amps and bluetooth modules with the same power source. It would be cool if it was built on the board.
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Old 26th January 2016, 08:32 AM   #4
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I2S out and CSR8675 should be considered.
This chip will also support aptX Low Latency.

Last edited by Fio; 26th January 2016 at 08:41 AM.
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Old 26th January 2016, 12:09 PM   #5
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Default CSR8645 Bluetooth 4.0 AAC APT-X Module / Baseboard

To me there are actually no (cheap) sources for CSR8675 boards available, so I'll stick with the CSR8645.

Most/All additional features from the 8675 aren't needed in a boombox setup and would need further programming.(6 microphones, 120mips DSP)

I want to keep it simple.

I'll look into power supply isolation and I2S. Dunno if I2S is available on the PCM header.

Last edited by doctormord; 26th January 2016 at 12:15 PM.
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Old 26th January 2016, 02:38 PM   #6
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So i talked to my colleagues, psu isolation isn't an easy problem solver here, as the audio is still (for SE) ground referenced and this might/will break the concept.

Possible solution would be step-up + 2-stage regulator design to rise PSRR and seperate bt-current from the rest of the system.

Beside this, I2S is available on the PCM header, need to check what power domain this runs from.
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Old 27th January 2016, 01:17 AM   #7
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So there's a first schematic.

http://www.diyaudio.com/forums/attac...1&d=1453857447
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Old 29th January 2016, 02:36 AM   #8
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Well, that escalated quickly.

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Old 29th January 2016, 04:15 PM   #9
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Looking good. What did you add/change? I'm a total novice at PCB design, trying to figure out what you have added is a challenge.
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Old 29th January 2016, 06:58 PM   #10
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It actually is a bit "overengineered".

Front left is USB input for data with USB-connect-detection via voltage divider to GPIO as the USB-bus-voltage is not used here at default. (And maybe never will) Then there is a POR-circuit for the BT-module to delay power-on until the voltage is stabilized and coupling caps are charged. The stuff around the inductor footprint is a 1.25Mhz buck converter with a coupled inductor layout to provide a second isolated voltage for the analog section which mainly consists of an R2R low-power dual-opamp. So the buck converter is bringing down 6-36V input voltage to 4.5V intermediate voltage. Both the digital and the analog part gets their own LDO to bring the voltage down to regulated 3.3V. On the rails there are several filter implementations.

As said, the analog stage is doing differential to single-ended conversion, but there's a header to get the differential signals as well. Secondly, the Mic/Line-in is brought out to a header via ac-coupling. Also there is the PCM/SPI interface which also contains I2S at the top left. This is feed through a 24Mbit/s bidirectional level-shifter. (1V8 -> 3V3)

Finally there a 2x 3.5mm jacks for output and external switched (bypassed) line-in.

So yeah, thats it.

Last edited by doctormord; 29th January 2016 at 07:01 PM.
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