Hackaday Supercon (2024-11-02)

https://cnlohr.github.io/lolra_talk

cnlohr / Slides rev B

• "Transmitting is the easy part" - Dad
  
  
  
  
  
  

Youtuber	Githuber

• Love exploring what microcontrollers are capable of without wads of abstractions.

*

https://youtu.be/XKnyAYKP434

https://youtu.be/j-QazXghkLY

https://youtu.be/-4d3PgEXhdY

https://youtu.be/GdECYJA4iF0

https://youtu.be/bcez5pcp55w

https://youtu.be/eIdHBDSQHyw

?

• Tiny computers
  • Run code, but have I/O
  • Basic CPU, 1-240MHz *
• Can we write software to
  • talk ethernet?
  • communicate over USB?
  • be a power supply?
  • broadcast FM radio? video?
  • broadcast LoRa® packets?
  • receive RF signals?

• No (or minimal) extra hardware
  • SPI, ADC, Timer, DMA? 😃
  • Resistors, Capacitors? 😐
  • A Transistor? 😬
  • Chips? Dedicated Features? 🙅
  • The cheaper the better 🤑
• 🧠 and some code
• Original chip designers expect impossible

• Use an ADC triggered off of timer
• Use DMA to save samples
• What about a ch32v003?
• They're cheap (~10¢)
  
• Actively playing with them

• Used internal PLL
• No external parts
• Cooked it up to 90MHz
• Modulated FM

• DIP-8 or SOIC

• OSCCAL (FM)
• PLL 8x
• OC1B and OC1B
• PWM is ÷3, but that's OK. We're square.

• Run ADC at F_s
• - odd + even
• Finds ½F_s
• Sometimes signal fades
• Picks up harmonics
• One add per sample

• Are just suggestions.
  

• "I" and "Q" running vars
• +--+, ++--
• Tunes only to ¼F_s
• No signal fades
• add and sub per sample
• Picks up harmonics

• Why can we receive them?
• Why are they so weak?

• Using Spreadsheets
• Simulate a signal
• Perform the operations
• Cancels out other freqs
• Harmonics (3x, 5x, ...)
• power = √i² + q²

• Requires multiple signals
• No hope of keeping up
• Precompute bitstreams in javascript
• Nothing worked
• Confusing Output
• Got an SDR - didn't match expectation
• What if we write a simulator?

code

• "Goertzel's algorithm is fun" - JoslynRenfrey (2020)
• "Goertzel's is 🪄" - cnlohr (2024)
• Goertzel's and DFTs are pixel perfect.
• Per sample, 1x add, mul, sub, mov per tuned frequency.
• Tune anywhere in spectrum.
• Easy to implement with integer math.

• FFTs
  • View received spectrum (can look at one output)
  • Had to bump up to the V203
  • No FPU (But fixed-point FFT OK)
  • 4log(n) operations per sample
• sin/cos correlation
  • Requires sin + cos per sample
  • Still too slow

• Implemented quadrature decoding
• Devkits are $4 on Aliexpress

• Digitally Controlled Oscillator
• Frequency Modulation (FM)
• Dithering
• PLL For Frequency Multiplication
• PWM For Output
• Harmonic Output
• Amplitude Modulation (Limited) (AM)
• SPI/I2S Output instead of PWM
• Reflections when direct sampling

• 144 MHz RISC-V, with mul
• ADC: 12-bit 1MHz---------- 4.8MHz------------ 9.6MHz
• Uses ch32v003fun
• More $$ than the 003 (30¢)
• Using a stock $10 devkit (no extra parts)
• Leverage Görg Pflug's Vector Scope

• calculator.html
• Started as static generator, now realtime
• USB Full Speed
• WebHID, Canvas, AudioWorkletNode
• Select "F_s" "Tune" "Windowsize"

• 900MHz (From a GPIO rated for 30MHz)
• 125 kHz channels
• Chirps
• Simple analog -> Sophisticated digital
  • Forward Error Correction (Up to Hamming-84SX)
  • Whitening Codes
  • Diagonal Interleaving
  • Gray Codes
  • Phases of Symbols
• "You'll probably get about 10-20 feet" - Dad

• No PWMs
• I2S Bus
• Playback pre-programmed bitstream per signal level
• One wire connected to "RX" Pin

• Works well with CB Radio (27MHz)
• Can receive at 100+MHz
• Broadcast FM demod different?

LoLRa

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• Random Sampling or "Compressive Sensing"
• WSPR
• Processor-to-processor
  
  
• Thanks Frank, and everyone in my Discord

•   ☹️ ☹️esp32-s2
  • APLL + PWM
•   ☹️ ☹️ch32v003 ch32v203 esp8266
  • SPI/I2S Bus
  • Created tables to mimic a chirp
  • Wrote LoRa® + LoRaWAN® protocol