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Implemented BFSK generation on mcu
05/09/2021 at 20:26 • 0 comments -
Soon in a μCtrlr near you
01/31/2021 at 21:10 • 0 commentsFSK is coming! (this was done in python to check my math, 3:2 ratio is used for illustration purpose only)
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DSO Screen Grabs!
01/03/2021 at 20:47 • 0 commentsThe illustrated 15ms interval is the maximum tolerable delay of desynchronization between voice and image, according to this article .
The 2 sine pulse train is generated on the DAC output of SAMD21 (with Direct Digital Synthesis rather than PWM) and is triggered by the appearance of a 1 PPS pulse from the GPS.
Note that the oscilloscope (low) sampling frequency is deliberately set to 50 kSa/s to get near to the audio recording frequency in cinema (48 kHz). Fitting of the sin pulse will be done on the desktop with available python libraries.
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Turning on the soldering iron
12/31/2020 at 04:12 • 0 commentsI've set up a gitlab repository for the firmware, ppssync, and cabled the prototype. Below is an artistically blurred picture of it:
The external antenna is for testing purpose only, the GPS is quite capable to fix indoor with its ceramic antenna. Here's the hookup guide between the Trinket M0 and the GPS board:
The trinket provides the 3.3 V power (from onboard regulator) to the GPS, greatly simplifying the set up! Thanks, Adafruit!
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Captain's Log, Stardate 000.0
12/07/2020 at 11:27 • 0 commentsTask list status:
- source boards
- test MTK3339 GPS module indoor fixing ability
- test SAMD21 direct digital synthesis (DDS) of a sin sync pulse with its 10 bits DAC.
- test SAMD21 hardware interrupts handling with the 1PPS signal
- buy a copy of AoE third edition
- research analog stage configuration
- order some LM358 (with extra magic smoke in them)
- move project home from Blogger (!) to Hackaday
- test waveform analysis on Kdenlive
- research NLEs handling of timecode metadata
- launch gitlab repository
- for firmware
- for PPSSoundmerge python desktop post-prod script
- final Arduino coding:
- code NMEA parsing on UART (use Adafruit lib?)
- code UTC time DDS FSK modulation to DAC
- desktop python coding:
- audio track analysis:
- sync pulse detection
- word decoding
- merge synced tracks with ffmpeg-python ⇦ I'M HERE
- analog stage:
- measure some input impedances (cam and audio recorder)
- implement reference voltage for true audio AC with LM358
- test mic level output
- test line level output
- test small speaker for acoustic coupling
Maybe I shouldn't reveal I've been researching this project for ten years! It would cast a shadow over my capacity to deliver... 8-) But you wouldn't have access to my treasure trove of related links...
The first traces of my journey are links kept on Delicious, now Pinboard: they are tagged smpte and date back to 2011. I later diversified my classification and introduced year after year more nuanced tags, here are direct links to them: (this is stratigraphic information paleontology!)
From now on, maybe the project will stall again... I'm back to school this January after a sabbatical semester (ducking down during COVID: I just can't stand doing zoom classes), we'll see.