Getting rid of annoying noise in the bluetooth audio adapter

As many of my fellow Gen 2 Prius owners know, we do not have bluetooth audio streaming capabilities in our beloved vehicles. Some have BT for phone, like mine does, but those do not play audio from a BT device that is not in telephone mode. So no streaming from our phones or other devices. For those cars that do have an AUX input to their audio systems, like mine, there are inexpensive BT adapters that will connect to the phone's music stream and output the signal to an analog stereo plug that can be connected with a cable to the Prius' AUX input. This is what I did and the little inexpensive device works great connecting to my phone and streaming whatever I want from the phone to the AUX input of the car. Seems like the end of story, but not so fast. Since the BT device plugs into the car's power outlet (via a USB adapter), it shares the ground between the audio input and its own power. At least my cheapo device does. This results in a very annoying noise that is always present on the aux input while the BT device is plugged into the AUX (and powered up). Drove me crazy for a long time. I knew the problem, but did not know a cheap and effective solution. Isolation transformers, etc. are not so cheap. The other day I found this DC-DC converter that seems to be tailor made for this solution. It's a 5 VDC in and 5VDC out converter, whose only purpose is to isolate the grounds between the input and the output. It costs $1.54. I have just received a few of these from DigiKey and created an adapter with a male USB plug on one end and the female on the other with only the power wires connected (date pins not connected on the plugs). The male end represents the input and the female the output with the DC to DC converter in the middle. I plugged my noise making BT adapter into my creation and it worked like a charm. No more noise on my audio BT stream from the phone. The little circuit can handle up to 200 mA of current (1W of power), but I measured my BT adapter consuming about 50 mA (0.25W of power), so it's a perfect solution to my noise problem!

Hope someone can benefit from this info. I bought 5 of these adapters because shipping is way more than the part itself. So if you think you want to try this, PM me and I'll send you one for a promise of a beer.

 

Guys, this adapter was pretty easy to make. You do need to find a female USB socket, though. I happened to have a cable that had a female USB on one side and micro-USB on the other. Not sure where it came from, but I used that and cut the micro-USB bit and then I used another normal USB cable to harvest the male USB plug. I then stripped both wires and found red, black and some other colored wires inside. Black and red are power and others are data. Black is ground and red is positive. Then I connected input of the DC-DC converter to a male red and black and output to the female red and black as indicated in the DC-DC converter data sheet. That was it. I then plugged the adapter into the USB power adapter and the BT device into the female USB part of my created adapter. That was it. It worked and no more noise. For less than $2. Well, I paid $8 for shipping, but I bought 5 of those things. I plan to make a few more of them and have on hand for future use. I need to find a cheap source of female USB sockets.

Glad you guys found it useful. This drove me crazy and I too had a rechargeable BT thingie, but that needs to be plugged in at some point and I do not need another thing I need to remember to recharge.

 

I provided a link to DigiKey in the OP. This is where I bought mine, not ebay or amazon. But here it is again.

 

I am not seeing the referenced item. But I am glad that designers are beginning to include the darned filter/isolator/whatever into the designs. I bought my part for $1.54 retail from DigiKey. This means it's a dime a dozen part and will not drive up the cost of the gadget that much. However user experience is greatly improved. I would say that if I ever got another one of these and it buzzed like mine does, I would return it with a bad review to stimulate the better ones coming to market. It's not that complicated a solution after all.

Now with the voice prompts, I really wish they would just not put them in at all. They are so annoying and ridiculous! Mine is blissfully devoid of them (must be an older unit) and just makes various musical noises when powered up, connected, etc. I really appreciate that aspect of it. These monologues all the devices produce nowa days are really grating on me. Siri, make it is stop!!! PLEASE!!!

 

NEVER! Nothing I need is ever missed by keeping the ad blocker on (or is it? I'll never know).