AM/FM Radio Gets Bluetooth Upgrade

For many commercial broadcast radio has lost its luster, leaving an unknowable number of perfectly serviceable AM/FM radios to lie dormant. But they don’t have to. As [Dan Gebhardt] shows in his recent hack, integrating a Bluetooth audio receiver into portable radio may be easier than you think.

For this project, [Dan] wanted to make sure no original functionality was lost. The radio still functions on the AM/FM bands, but now with the flip of a switch, he can listen to the audio coming his way courtesy of a Apt-X low-latency Bluetooth receiver. It sounds like the link is quick enough that he can even use this as a wireless speaker for watching TV, which isn’t always possible with cheaper chipsets that introduce a noticeable lag.

Isolating the audio trace.

The trick was to track down the receiver IC, a Silicon Labs chip similar to ones we’ve seen used in a few DIY radio projects previously. A peek at the datasheet told him which pins were carrying the audio signal, and after following them around the board, he found a convenient spot to cut the trace before it went into the volume control. From there is was just a matter of wiring in a SPDT slide switch that allowed him to select which device was passed through to the radio’s audio hardware.

While he had everything apart, [Dan] exorcised the Apt-X’s original 300 mAh LiPo pouch and replaced it with a DC-DC converter connected to the radio’s battery compartment. This allows him to run all of the hardware off of the same set of rechargeable NiMH cells, and also provides considerably improved runtime for the Bluetooth receiver.

Now as for physically integrating the Apt-X into the case of the radio…well, what can we say? [Dan] admits it’s a bit rough, but then the point was never to enter the thing into beauty pageants. It works well enough for his purposes, and in the end that’s all that matters.

13 thoughts on “AM/FM Radio Gets Bluetooth Upgrade

  1. It’s a old radio hackers/technicians trick. the volume control is where you find the audio signal (ready to be attenuated for the pre amp) i know in modern designs an audio processing chip may use a dc level from the volume to control gain but in the most existing designs just go straight to the volume control. to test you can “inject an audio signal” . ie: touch the middle pin with your finger and you should here induced mains noise from the speaker. Amplifier rescue tip. if you get an old HiFi amp with a “crackly ” channel (quite common) you usually don’t need a schematic to find the pre amp transistors (most likely culprits) . just replace the one closest to the volume control chances are you’ll have guessed correctly (if not change the next closest ones) small signal transistors are only a few cents each.

  2. OK, firstly that looks as ugly as a baboon’s ass! And secondly it’s a good idea, but the take away I would take is injecting an audio signal into the radio. If you just use this hack to put an input jack into a nice sounding radio you could have much better audio from your phone, and you can probably get a nice sounding radio at Goodwill. And just to repeat this thing is a Frankenstein’s monster, ugly but gets the job done.

    1. Did something similar a few years ago to a good “3-in-1” with no external input, in which the tape deck has stopped working (and I don’t own a single cassete tape anymore) : wired the audio signal from the tape deck section into an RCA jack pair added to the back; a chromecast audio was added and now I have spotify on this old system with huge speaker towers.

      To select the audio from the chromecast I have to hit “play” on the tape deck (the motors where disconnected so there’s no mechanical noise)

  3. Ahh. I really should do a writeup of the ghettoblaster conversions i’ve made.
    My conversion does not alter the exterior, nor does unreversable damage inside. I find the switch points where the amp is switched from radio to cassette and inject the signal there. But i go further: power is tapped from the cassette motor and I glue a spdt pushbutton so that when a tape is present, the motor is powered and without cassette, the bluetooth device gets power ( via a bucket converter) press play without cassette and the bluetooth module turns on. In one akai one i also glued in two buttons to activate next an previous to the ff. and rew. knobs because i had some space. In a grundig one Ialso converted I did it with reed contacts and two magnets. Works like a charm and the bewildered faces of people are priceless.
    Actually the most problems i have is that I cannot find a way to change the bluetooth name of the device, so I end up with six devices with the same name in my phone, making connecting a hit and miss affair.

    Oh. I did a writeup. Sorry about that. Must make a video i think.

    1. If you have time, I would love to see a full writeup with pictures of this project! I’ve been working on adding Bluetooth to a Sony cassette radio for my sister and tapped into the output of the cassette’s pre-amp but when I switch the bluetooth on, the cassette motor comes on too and there’s a buzzing noise which I think might be a ground loop or something. Your solution of the pushbutton is very neat! I drilled a small hole in the back of the case for a switch. It’s not pretty but you can’t see it.

      1. Hey thanks! I have used some VHM-314 modules as they are laid out nicely, have an onboard LDO and actually have the buttons to control forward and back. I will look for a serial connection on those, but on a first glance they may not have been broken out on this board.
        the first conversion was with a Bluetooth module i bought at Action here in the Netherlands, but the sound quality is horrible. as I still have one VHM-314 V2 board in stock, I might trying to replace it and make pictures of how i did it, but they will be not of any use, unless you have the exact same type of cassette player. the Grundig is a small one, the RR-660. the Akai is not at my place atm, so I cannot tell what type it is. the module is not even glued in place but stuffed in a zip lock bag and stuck somewhere so the antenna is not covered by large pieces of metal and does not interfere acoustically with the preamp. a solid ground connection is very important as well.

  4. Thanks for the great writeup! I’ve been reading the site for a while and finally thought of a project worth contributing.

    A 3d printed fairing for that ugliness is on my list.. a bit far down the list… Of next projects.

  5. Not a hack really, but I’m just using a couple of dollar store BT stereo to 3.5mm jack receivers in a couple of thrift store “ipod dock” type things that had a 3.5mm aux input. Unfortunately, that seems to have been a one off thing they had, and I only bought two, have about a dozen uses for them now I know they work.

  6. Ok. It works, if that’s what you need. Myself? I would’ve just wired in an external input jack. So many more options.
    I guess I was just never a BT fan. Kind of like ordering a fine meal, but instead of a chef preparing it and the waiter serving it to you, it’s just downloaded from a file on the replicator, and Scotty beams it to your table. There’s a lag between the food hitting your mouth and the flavor, and there’s always that aftertaste of buffering.

  7. Rather than rail against BT I read up on APT etc. on Wikipedia and I knew that 5.0 can be hifi but the bewildering array of levels and densities my oh my! Some transmit with open source but closed on the receive end chip and can get scummy with copy-cop crap. Delay seems to still be an issue. Want to figure how many micro seconds an FM transmitter’s signal takes to get thru the radio? I don’t have pay for Armstrong’s patents.

    So how to find what my phone sends or everyone else at the party that wants to play thru what device’s specs that I’d want to buy into for the receive end. It’s a heck of a mess compared to headphone jack wired. There’s no such thing as just plain ole Bluetooth anymore.

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