Intro to PCB’s

All things pcb

I am finally getting around to posting some documentation on bluetooth audio adapter that I intend to make my pcb final.


After a really long wait, I got the parts from spark fun and connected them to a breadboard.  First the RN52 breakout board.  Since I just want the audio, and no other functionality, I just have to provide power.  However, in case in the future I would like to prototype a board with all of the functionality that the chip has to offer I have connected an FTDI breakout to explore the chips programming functions.

20161001_221306 20161001_221239The chip requires a pull down to ground via GPIO9  to enter the command line for the chip to make alterations such as button capability like seek reverse vol up or down etc.

20161001_221245 20161001_221306 20161001_221228


Here is a picture of the command line in terminal showing that the IC is connected.20161002_214552 20161002_214547

On the first try, the board would only remain connected for limited amounts of time to a bluetooth device such as a phone or a laptop.  That turned out to be a power issue.  The FTDI was backfeeding enough power to power the board, but it was not enough for the broadcast to be stable.

Turns out I was not sending the recommended 6-12 volts to the 3v power breakout board.

Moving on, I experimented with the board to make sure it remained stable once I added the correct voltage, and everything worked great.  I was able to listen to music for 4 hours with no interruptions.  It is not line level signal, so it may be in the future I will add a amplifier to the output of the RN52.


On to the schematic,



I am going to acid etch since my traces are very small and the printer resolution is better than the other mill.

here are the results of my trying to toner transfer onto the copper.

20161016_223132 20161016_223123 20161016_223119 20161016_223109

needless to say that was not as easy as I had thought it would be.  It turns out I was not heating it up hot enough to get a clean transfer.

I have since continuity tested all of the connections on the board, and out of the two boards there was only one problem but it could have been catastrophic.  The VCC was connected to the ground plane due to the two traces being to close and the acid failing to etch the copper away.  I used a xacto knife to cut away the copper and tested again for continuity and the problem was resolved.

I cut out the stencil for the solder paste today according to the instructions on the class blog though it took a few tries to get the right settings and sizes for the pads, and will try to solder mask at least one of two boards that I was able to get etched tomorrow.

I tried to apply a solder mask two separate times however for some reason it did not work, not sure why.

20161019_170133Since the solder mask didn’t work, the solder stencil was difficult to apply the solder paste and as a result led to improper connections and shorts that I have as yet been unable to sort out.

Picture of the board with parts mounted.

I went back home just before the summer and when I got there I was doing a lot of driving.  I have a couple of RF adapters in my car to plug in my phone and ipod, and I got to thinking.  I have been working with micro controllers this year, and I bet there is a way for me to clean up all of the wires in my truck by using an arduino and bluetooth.  So when I returned to NY, I started looking online for a tutorial that might make it possible to make a bluetooth audio receiver that I could plug into the aux jack in my truck.  It turns out that the way that data is transferred with bluetooth and the memory constraints of arduino, it was not possible.  Undeterred I kept looking for a way to make this happen. Ultimately I came across a surface mount chip called an RN-52, which is a bluetooth digital audio receiver chip.  Sparkfun sells the chip as surface mount and also with a breakout board, and has a tutorial for exactly what I need.

Sparkfun’s tutorial utilizes all of the features of the chip, data in/out, and sound.  I am only interested in utilizing the sound for my device, I can make changes such as volume up and down, track back and forth, etc on my phone which rides in its holder in my car.  I am only interested in getting the audio to stream to a 3.5mm jack so I can plug it into my car stereo receiver.


The parts list for this device is the rn-52 breakout board, and a basic 3.3v breakout board to manage the power.

Here is the schematic and the proposed changes to suit my needs. I will use a arduino pro mini for the serial UART as a substitution for the sparkfun UART.