Antique Car Stereo Bluetooth Audio Retrofit with ESP32 - Page 1
Forum section: electronics / projects

author: jcrubin
author_rank: Frequent Contributor
timestamp: March 23, 2022, 09:21:41 pm
content: I'd picked up another Sapphire 9 radio, this time its only a repair, not a restoration, left in the original patina, and it seems in good condition. I was however asked if an auto-switching Bluetooth module could be designed for such a unit. Not one with a switch but automatic like a modern radio. This took some thinking.Id decided to go with an ESP32 as a platform for this using a PCM5102 DAC as a compliment. I'd quickly found 2 areas for possible install, but first a design would need to be established.A library from Phil Schatzmann exists in the community to provide an easy interface between the bluetooth and the DAC. A proof of concept is up and running quickly, I try it out on the Dynaco ST-70 and its working good.Id chosen the voltage regulator as the voltage can be specifically selected, but their implementation was crap, and it was difficult to work with, I suffered through a few of them before cutting of the pot before figuring out the trace cut.A power budget is then taken, i find it way below budget so I'm not concerned.When more parts arrive well continue in chapter 2.

author: jcrubin
author_rank: Frequent Contributor
timestamp: April 07, 2022, 12:26:40 am
content: With the parts needed to continue we can now move on with the repair of the radio itself, aw well as a cleaning and service of the unit, however, a restoration is not authorized.With the radio repaired and tested a good point for power pickup is determined. It will be switched power so that the ESP32 and associated components turns on and off with the radio. In the mean time i've been soaking the ground lug which was completely rusted, eventually it broke off. I dropped a new bolt of the same size right in.The 5 volt regulator was connected into the switched power of the radio and tested good. We can use the radio as a power source going forward.The mux is then designed into the circuit so that the AM and Bluetooth signals can auto switch into the radios pre-amp input. The mux switching is controlled by the ESP32.To make things more interesting, Ive digitized my voice into the esp32 when the Bluetooth connects and disconnects. After testing out the voice an analysis is done to determine the best point to inject the signals back into the radio. Schematic point 13 is determined.Wiring in both AM and Bluetooth into the mux and the output to point 13 allows for a full running auto switching system working as designed.The next chapter will deal with fitting all of this into the unit.

author: jcrubin
author_rank: Frequent Contributor
timestamp: May 05, 2022, 09:32:26 pm
content: Now in part 3 the system as designed must be reduced in size as to fit in the radio. It didnt occur to me that the bluetooth wouldn't work once the cover was closed so I'd order a special one with an SMA adapter.To reduce the chance of shorts, only the pins used were added to the board. when soldered to the proto-board, the several connections should be sufficient. I did find however that this model ESP32 has an LED that uses a GPIO that I use for my hardware, so I had to made an adjustment.Wiring was done carefully, stopping at intervals to test and make sure i hadn't broken anything. With the wiring completed, the back of the chassis was prepped to ensure nothing protruded that didn't need to. Also the back of the existing board was dressed.At this point I started cutting down the proto-board to size. Careful measurements are used to get the standoffs drilled into the right position.A microscopic resistor has to be relocated on the ESP32 to move to external antenna, I ended up using hair thin copper wide for this task.At this point the board was installed in, the mounting bracket, slightly modified to support the second board.With everything installed the Eb/NO was not good, so I had to make some changes and install shielding. A before and after test is conducted.

author: jcrubin
author_rank: Frequent Contributor
timestamp: June 17, 2022, 11:43:44 pm
content: Chapter four was not planned, but I was simply not happy with the outcome of the installation. There was, even with the abundant shielding, too much noise from the installed components, compounded with the de-tuning of the RF section by its close proximity to it. This was aggravated by the fact that it was an obstruction, providing no way to return the coils with the added equipment.In the very first chapter i'd mentioned an alternate location for the components, forward and to the left, where no electronics exist. I'd avoided this as it was a more difficult option but now it was the only way to do this acceptably.The board was removed and the ESP32 was relocated. Testing at regular intervals it was determined that both the ESP32 AND the regulator was effecting the RF section, so both of those were relocated. The DAC and mux remained on the circuit board, though the board was shifted away from the RF section.the result was a complete removal of the artifacts even without the addition of internal shielding. also, the coil adjustments were no longer obstructed.