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A project log for Mini WAV Recorder

Mini WAV recorder based on STM32G030F6P6 and I2S microphone

maksymMaksym 04/16/2022 at 17:450 Comments

I recently received PCBs for my project from JLCPCB (not sponsored :( but it's cheap anyway ). They were designed in KiCad and in my opinion turn out well, but it's just 2nd my PCB design for production so there is room improvment for sure.

I'm soldered it using cheap soldering station and fine tip. A bit hard to solder was only the MCU and I damaged one PCB trace during this process, but the rest was really easy. I added display and microphone module after I programmed MCU.

Then I checked if everything is working and mounted li-po battery and tp4056 charging module by double-sided tape on back.

I choose battery with capacity of 550 mAh what should result in about 27 hours record time and 4 years of standby time (teoreticly).

Driving "big" quartz with STM32

I used not SMD version of crystal oscillator because at the time available SMD version prices in local shops were a joke. Its have high capacitance of probably 12.5pF (common value for this size I don't have datasheet) so according to documents from ST it require to change something called drive capability. But I don't getting it because, setting anything else than low cause RTC to not work. At low setting it's working but touching crystal with oscilloscope probe (or hand) cause it to stop working (RTC stops counting) and I'm not seeing anything on oscilloscope so signal must be really weak. If someone knows something more about this subject I will be grateful for comment.

Anyway I set time and let it running. After one day I noticed that it's hurry by one second. Then another day and another second. STM32 RTC have calibration register so after some math by eye I set it to 34 and now it's one second late after 3 weeks so I hit good spot. 

3D printed case and fail

I designed case in Fusion 360 and print it on Ender 3 however I thought that it's looking too much like a brick and decided to design something less "bricky". Microphone breakout board was a big obstacle to this goal so I decided to desolder it, cut goldpins, and solder it on wires as flat as possible. I didn't wanted to move battery now so I done it from front. It was hard and irritating job to remove it and after that I noticed that goldpins were soldered from other side to microphone board too because I destroyed two traces. I tried to fix it but there was only very small point of copper just basiclly on microphone itself. I'm succesfully soldered thin wire to it and put evrything together but microphone was damaged. I'm don't know if it was too much heat but it's theoretically working but at max gain I must shout to be able to hear something on recording that is very deformed. Now I have to order new modules from China. So probably next and final update in 2 mounths at least. I could order it locally but I'm not really need that project (just for hobby and learning) so I don't want to pay over 400%.

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