Imported from GitHub: J-K-Kowalski/PCSK225-PICO2 · commit e403393 · license BSD-3-Clause

Description

PCSK225 Pico2 SDR Receiver

README

PCSK225-PICO2 SDR Receiver

Overview

• Direct sampling with a high‑speed external ADC (ADS7049)
• Optional SSB down‑conversion using a Si4537‑D60 tuner, enabling baseband sampling with the RP2350’s internal ADC

Key Features

• MCU: Raspberry Pi Pico 2 (RP2350) module
• Direct RF sampling: ADS7049 12‑bit, high‑speed SPI ADC connected to the RP2350 (supports ~225 kHz IF/baseband sampling)
• Optional tuner: Si4537‑D60 for SSB-style down‑conversion to low IF/baseband for sampling by the RP2350 internal ADC
• RF front end:
  • Active 6‑pole Butterworth band‑pass amplifier around TLV9064 (U2) centered on 225 kHz
  • Output/driver amplifier for Si4537 based on TLV9062 (U1)
  • TMUX1204 analog multiplexer (IC1) for flexible signal routing between ADCs and front‑end nodes
• Timing: DS3231 RTC with CR2032 backup battery for stable timekeeping and 1 Hz/32 kHz outputs
• Displays:
  • On‑board 0.96" I2C OLED (SSD1306)
  • Header for an external graphic LCD
• I/O expansion and storage:
  • PCA9500 I2C port expander with integrated EEPROM for configuration storage
• Connectivity and power:
  • Micro‑USB (Pico 2)
  • USB‑C connector for powering the receiver and PC connectivity
• User I/O:
  • 8 general‑purpose digital I/O lines on headers
  • PWM‑driven speaker/buzzer output with buffer stage
• Form factor: single PCB with Pico 2 module, mounting holes, and on‑board connectors
• See pcb.jpg for a 3D view of the assembled board

Signal Paths

• Direct 225 kHz path:

1. Antenna/RF input → active BPF (U2 TLV9064) → analog mux (IC1) → ADS7049 → RP2350 via SPI/DMA
2. Intended for coherent sampling/decoding of the Polish 225 kHz time code

• Optional SSB/down‑conversion path:

1. RF input → Si4537‑D60 → low‑IF/baseband → output amplifier (U1 TLV9062) → RP2350 internal ADC
2. Useful for alternative demodulation modes and experiments

Subsystem Details

• Active BPF: 6‑pole Butterworth around 225 kHz using TLV9064 quad op‑amp, input protection, and gain‑setting network
• Analog MUX: TMUX1204 routes filtered RF to the external ADC or other measurement points
• External ADC: ADS7049 low‑latency, SPI, suited for continuous streaming to RP2350 (DMA recommended)
• RTC: DS3231SN provides INT/SQW and 32 kHz outputs; backed by CR2032 cell
• Displays:
  • SSD1306 OLED on I2C bus (address configurable via jumpers)
  • External LCD header with SPI/I2C signals as routed on the schematic
• I2C Expander/EEPROM: PCA9500 provides extra GPIO and non‑volatile storage for calibration and user settings
• Audio: small speaker output driven from MCU PWM through a buffer (74LVC1G34) and filtering
• Power:
  • 3V3 rail with local decoupling (X5R/COG capacitors as noted)
  • USB‑C and Micro‑USB power options; VSYS routed to Pico 2
  • Ferrite bead and RC elements for analog rail cleanliness

Firmware Notes

• Platform: Arduino core for RP2040/RP2350 or Pico SDK (C/C++)
• Recommended peripherals:
  • SPI DMA for ADS7049 streaming
  • PIO or timers for precise sampling clocks if needed
  • I2C for OLED, RTC, and PCA9500
  • PWM for speaker/buzzer output
• Example tasks:
  • 225 kHz band‑limited sampling and digital demodulation/decoding (e‑Czas/time code)
  • SSB/low‑IF capture via Si4537 with on‑chip ADC
  • UTC timekeeping using DS3231 and PPS alignment

Connectors and Interfaces

• Pico 2 module header exposes GP0…GP21, ADC pins, SWD, 3V3, VBUS, VSYS
• OLED I2C header and external LCD header
• USB‑C and Micro‑USB
• 8x GPIO header for user applications
• RF input and test headers as shown on the schematic
• Speaker/buzzer connector

Bill of Main ICs

• RP2350 (Raspberry Pi Pico 2 module)
• ADS7049 (external high‑speed ADC)
• Si4537‑D60 (optional tuner/down‑converter)
• TLV9064 (quad op‑amp, BPF and buffering)
• TLV9062 (dual op‑amp, output driver)
• TMUX1204 (analog multiplexer)
• DS3231SN (RTC)
• PCA9500 (I2C GPIO expander + EEPROM)
• SSD1306 (OLED controller)

Status

• Hardware: Rev. 2 schematic/PCB
• Image: see pcb.jpg for the assembled PCB render
• Firmware: work in progress

License

• Hardware and firmware: A permissive license similar to the BSD 2-Clause License, but with a 3rd clause that prohibits others from using the name of the copyright holder or its contributors to promote derived products without written consent.

Acknowledgements

• Designed by KJK Innovations for research and development of low‑frequency time‑signal receivers and SDR experimentation.