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Old 22nd Sep 2022, 7:35 pm   #1
Radio Scotland
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Default Converting a vintage car radio to Bluetooth.

Never done it before but seems pretty straight forward. Only thing I'm not sure about is how to combine the Bluetooth's two stereo channels to get a mono output.


Any help appreciated.
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Old 22nd Sep 2022, 8:02 pm   #2
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Default Re: Converting a vintage car radio to Bluetooth.

I just connect the 2 outputs together on the bluetooth module. The main issue is location, as fitting a module inside the radio results in a very high signal attenuation because of the all metal, earthed case. Personally I fit the BT module externally as part of the wiring loom, encasing the module in heat shrink.
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Old 22nd Sep 2022, 8:21 pm   #3
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Default Re: Converting a vintage car radio to Bluetooth.

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Originally Posted by agardiner View Post
I just connect the 2 outputs together on the Bluetooth module. The main issue is location, as fitting a module inside the radio results in a very high signal attenuation because of the all metal, earthed case. Personally I fit the BT module externally as part of the wiring loom, encasing the module in heat shrink.
Just done a bit of research on the subject and apparently you need to use matching resistors on each stereo channel to isolate them from each other,

As for the Faraday cage effect i suppose you could hook a short piece of wire to the Bluetooth modules PCB printed antenna and have it protruding from the rear of the radio,

Plan is to use the radio's preset button to switch between the radio and Bluetooth, Some people disable the radio and have it Bluetooth only but not my thing.

Having a few mod con's makes these vintage radios more desirable, Not many people driving around listening to AM Radio's these days.
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Old 22nd Sep 2022, 9:18 pm   #4
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Default Re: Converting a vintage car radio to Bluetooth.

It helps to use a pair of matching resistors, but it's not absolutely essential. The value isn't critical - 1k-4.7k is probably the right area, though it depends on the input impedance.
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Old 22nd Sep 2022, 9:22 pm   #5
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Default Re: Converting a vintage car radio to Bluetooth.

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It helps to use a pair of matching resistors, but it's not absolutely essential. The value isn't critical - 1k-4.7k is probably the right area, though it depends on the input impedance.
Cheers paul, Was just watching an audio engineer on youtube and he say's the above values are about right.,


Jay
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Old 23rd Sep 2022, 2:20 pm   #6
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Default Re: Converting a vintage car radio to Bluetooth.

Well iv'e disconnected and bypassed the LW Preset, It's a DPDT Switch. One side of the switch will be used to switch between radio audio in and bluetooth audio in.

The other side could be used to turn the bluetooth off to prevent break through when listening to the radio,


But think there might be radio break through when using the bluetooth, So the other side of the switch could be used to switch out the radios front end when using the bluetooth,

Need to experiment to see what the best switching options are.

Plus a few blue LED's in the tuning scale
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Last edited by Radio Scotland; 23rd Sep 2022 at 2:28 pm. Reason: extra info
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Old 24th Sep 2022, 2:37 pm   #7
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Default Re: Converting a vintage car radio to Bluetooth.

Scrapped the bluetooth idea as i came across a long forgotten about tiny MP3 player i have which also has a built in FM radio. So i wired in an aux jack using 3.3k matching resistors, Sounds great


Was getting bleed through from the original AM radio so wired it so the AM aerial is out of circuit when the switch is in the aux position, switching between aux and the radio is done via the auld preset button
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Old 24th Sep 2022, 10:52 pm   #8
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Default Re: Converting a vintage car radio to Bluetooth.

Nice result.
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Old 27th Sep 2022, 2:37 pm   #9
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Default Re: Converting a vintage car radio to Bluetooth.

Just received the bluetooth module and for the price (4 quid) it works great, I'm curious to find out the current draw of these modules and can't find any specs online, Can't measure it using my DMM as im currently powering it from a USB Cable, Expect it won't be much,

Curious as i'm thinking of using a 5v 1w zener to power it once it's installed in the radio, Yeah iv'e reverted back to my original plan

Might even fit one in my home HI-FI
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Old 27th Sep 2022, 2:51 pm   #10
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Default Re: Converting a vintage car radio to Bluetooth.

Rather than messing around with Zeners, what about using one of the little 3-legged 5V regulators like the 7805? The 100mA version will do just fine and will do a better job of removing any alternator whine than a simple Zener.
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Old 27th Sep 2022, 2:55 pm   #11
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Default Re: Converting a vintage car radio to Bluetooth.

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Originally Posted by G6Tanuki View Post
Rather than messing around with Zeners, what about using one of the little 3-legged 5V regulators like the 7805? The 100mA version will do just fine and will do a better job of removing any alternator whine than a simple Zener.

Was thinking of using a zener for simplicity, It isn't installed in a car at the min, But will probably end up selling it at some point, So yeah a proper regulator might be the way to go,



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Old 27th Sep 2022, 7:24 pm   #12
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Default Re: Converting a vintage car radio to Bluetooth.

Apart from the 5v regulator which is definitely the best way to supply the 5V, you may find that it is necessary to add a 5v:5V isolated supply (B505S 1 W) to remove unwanted whistles and other odd noises which are often prevalent if using a common supply.
I've bluetoothed many radios and some are OK without (DAC90A for instance) whereas others are definitely not. They are very cheap and small. I find best module is the KRC 86B.
I normally add 1K resistors in the left & right outputs although I have found just 100 ohms to be OK as well.
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Old 27th Sep 2022, 7:38 pm   #13
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Default Re: Converting a vintage car radio to Bluetooth.

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Originally Posted by Colin Boggis View Post
Apart from the 5v regulator which is definitely the best way to supply the 5V, you may find that it is necessary to add a 5v:5V isolated supply (B505S 1 W) to remove unwanted whistles and other odd noises which are often prevalent if using a common supply.
I've bluetoothed many radios and some are OK without (DAC90A for instance) whereas others are definitely not. They are very cheap and small. I find best module is the KRC 86B.
I normally add 1K resistors in the left & right outputs although I have found just 100 ohms to be OK as well.
Thank's for that, Never messed about with bluetooth modules before so its all a learning curve, I take it you mean supplying the module power via a internal separate power supply or do you mean a separate external supply ?


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Old 28th Sep 2022, 3:05 pm   #14
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Default Re: Converting a vintage car radio to Bluetooth.

Not one for the purist Originally the radio didn't have a tuning scale light only a dim on light
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