Wee Noise Maker Discovery rev-A

As I said in the first post, I rushed to produce a first PCB to try my new idea as fast as possible. The first board was just a matrix of buttons and LED, it worked OK and gave me the motivation to continue this project.

Wee Noise Maker Mk-I rev-A

For the second board - named Wee Noise Make Mk-I - I decided to make a stand alone project with the MCU, audio codec, OLED screen, power supply, battery charging, SD card, etc..

When the Mk-I rev-A PCB arrived from SeeedStudio, the first thing I noticed is that I completely screwed up two footprints, the encoders and the voltage regulator… To be honest this is really unacceptable. I should always print the PCB to scale on a piece of paper and check the footprints before sending the design for production. The encoders I could still plug them in by bending the pins but the voltage regulator was completely off (TSOP vs HTSOP).

Anyway, I started by soldering my first LQFP-100 package the STM32F4 - it is not as bad

as it seems - and all the passives around it, then I tried to program and run it. It worked! That was great. The battery charging and OLED screen were also working as expected.

The last main component to solder was the SGTL5000 audio DAC, a QFN package. I watched a few tutorial to learn how to solder this kind of package but it seemed difficult so I wasn’t very confident.

Once it was soldered, I tried to make the MCU talk with the DAC over I2C but got no answer. At some point I realized that my circuit was really bad. A dumb error again, this time with decoupling capacitors… This was the second major failure on this board, time to make a new revision.

Wee Noise Maker Mk-I rev-B

For rev-B I got all the footprints right \o/ But the DAC was still silent :(

After a few hours debugging, inspecting the schematic and reading the documentation, I realized that one of the three power supply pins has to be at 1.8V (vs 3.3V for the others), it meant I had to add an extra voltage regulator. Let’s go for rev-C...

Wee Noise Maker Mk-I rev-C

I received the rev-C board early June and soldered all the components right away. Once again everything was working except the audio DAC. The chip wasn’t responding to I2C messages.

This time the error was not really in the hardware design. I found in the documentation that the SGTL5000 needs an external clock to start working. This external clock is actually the master clock (MCLK) of the I2S protocol, so I have to send I2S data before being able to talk with the DAC. Once I figured this, it took no time to have Wee Noise Maker produce its first sounds!

Now that I can play sound, there’s still two features I need to check: sound input and SD card. Once I validate the hardware for those to I will start to focus on the software.