Tuesday, August 2, 2016

Bluetooth music for older car stereos

I have a ten year old car with a stock stereo system. It includes hands free calling using Bluetooth, but it does not support music being piped into the system that way. Instead, it has a set of RCA audio and video jacks and a 12V cigarette lighter port hidden in the center front armrest. It seems like a poor design, but the intent of this auxiliary input was for a portable DVD player. I guess they thought there would be a big demand to play movies on the navigation screen when the vehicle is parked. (The video is disabled when driving, but the audio continues to work.)

Most Bluetooth third-party accessories for car audio assume there is no Bluetooth support whatsoever. I only want to send my phone’s media audio via Bluetooth to a receiver hidden away inside the center armrest. I want the existing functionality for phone calls to remain as-is. Almost all of the “no frills” Bluetooth receivers on eBay, etc. suffer from poor design and build quality. I took a chance with this product: Logitech Bluetooth Audio Adapter for Bluetooth Streaming. It wasn’t designed to be used in a car, but it had a lot of good reviews and included features that were essential for this project to work properly. The new receiver needs to turn itself on when the power is applied (i.e., car starts) and it must allow my phone to automatically connect. It makes no sense to buy a product that I have to manually power up or requires me to re-pair with my phone each time I start my car. I don’t know how well it works with two phones. I know you can pair two devices, but I don’t know how it handles multiple device precedence, if at all.

The biggest challenge is getting power for the new Bluetooth receiver from the car. Most modern electronic devices not made by Apple or Nintendo use microUSB ports for power, but this device does not. The good news is that its voltage requirement is five volts, so a run-of-the-mill USB power adapter for a 12V power port (i.e., cigarette lighter) and a USB to coaxial plug adapter can be obtained pretty easily. A ready made cable can be purchased for under $2 through Amazon or eBay, but will most likely be shipped from China. I was able to make my own cable by using parts from an old USB mouse and an orphaned wall wart that happened to have the same plug size as the Logitech receiver.

Analog audio ports in vehicles are susceptible to noise due to improper grounding. The electrical ground of the vehicle may not be the same as the audio jacks’ ground. A noticeable hum or crackling is a sign of this condition. The solution is to use a ground loop isolator. It contains two 1:1 audio transformers, one for each audio channel.

The Logitech adapter includes a 3.5mm stereo to RCA audio cable. Considering it has both of those as outputs, you should be able to use that cable with either format auxiliary input the car stereo provides.

Diagram of circuit.

Parts list


It’s difficult to provide precise instructions since there are too many variables to consider. Basically, plug the Logitech Bluetooth Audio Adapter to whatever auxiliary input the car stereo provides. Power it with the USB cable specified in the parts list assuming you have USB power available. Pair the adapter with your cell phone and try it out. If there’s noise or buzzing, insert the ground loop isolator between the car stereo and the Logitech Bluetooth Audio Adapter.

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