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Bluetooth for vintage stereo
Bluetooth for vintage stereo
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Old 5th August 2018, 09:01 PM   #1
marcjero is offline marcjero
diyAudio Member
Join Date: Aug 2018
Default Bluetooth for vintage stereo


I'm not sure it's the best place to discuss about this topic. So I apologize if I'm wrong.

Anyway let me explain a bit what I'm looking for.

I own a 20 years old car that includes a non din head unit. The unit is not bad : it drives 2 main speakers and 2 tweeters and crossover is supported. So I plan to keep the unit as is (and preserve the interior aspect) and just add the bluetooth feature I'm missing.

The harness of the unit is ISO. It includes an input line (analog) for a CD Changer. So I think I can use a bluetooth module and just send the audio to this line. Not very complicated and I don't expect to control the playback from the headunit.

The head unit includes a phone mode. Basically there is an input line for phone audio in the harness. There is also a mute pin : if the pin is grounded, music is muted and phone audio is sent to the front speakers.

So I would like to keep the phone mode. I think I can connect the bluetooth audio chanels to the CD changer and phone lines. But I also need to ground the mute pin when the bluetooth is switching to HFP mode (hands free). And to be honest for now I didn't find any bluetooth module or gateway that provides a signal when this happens. Why keeping the phone mode ? Because it works when listening any kind of source and it can even wake up the head unit when receiving a call.

So do you know any magic bluetooth module that I could leverage for this diy ?

Thank you guys.
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Old 5th August 2018, 10:40 PM   #2
Perry Babin is offline Perry Babin  United States
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Join Date: Nov 2003
Location: Louisiana
Until you get a direct reply here, try browsing the Crutchfield website for possible solutions.
Anyone who purchased the repair tutorial, email me (babin_perry@yahoo.com) if you want to download the latest version.
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Old 6th August 2018, 11:30 AM   #3
toronja is offline toronja  Argentina
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Join Date: Mar 2008
Location: Santo Tome - Santa Fe - Argentina
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Marc you can share brand and model of your audio unit?
In most of cases the unit have an DIN conector and need to ground one line through 1k resistor to activate the input.
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Old 6th August 2018, 09:18 PM   #4
marcjero is offline marcjero
diyAudio Member
Join Date: Aug 2018
It's a stereo for a Smart Roadster, made by Grundig. Manual available here : https://www.evilution.co.uk/files/sm.../grundigcd.pdf

ISO pinout : SMART Car Radio Stereo Audio Wiring Diagram Autoradio connector wire installation schematic schema esquema de conexiones stecker konektor connecteur cable shema

I think grounding C8 will enable the C11,C12 line . (see PHONE IN option in expert settings)

C18,C19 and C20 could be used for music.
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Old 8th August 2018, 09:56 PM   #5
marcjero is offline marcjero
diyAudio Member
Join Date: Aug 2018

I found that CSR8670/75 chips can activate a PIO when a phone call is started. It looks like that it's "just" a configuration job.

So I guess I need to :
-find a good bluetooth sink board that is using the CSR chip

-then update the configuration of the chip
-wire the PIO pin to a relay that will ground the mute line of the stereo
-wire output line and mic line to the ISO harness

Is it as simple as that ?
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