GPS Frequency Standard

Build V2 Features

Stand-alone design does not require PC. Generates a 10 MHz output after satellite lock.

Hackaday project page
NEO-7M GPS
- Right Angle external antenna connector
QTPy49 card
- CircuitPython code fits into QT Py (SAMD based)
  - QT Py (RP2040 based) could be used as alternative
- 3.3V, 48 MHz
DRIVE50 - 50 Ohm coax card
- Receives input from GPS output and drives 50 Ohm output on BNC
Status LED
- Blinks in for 1 second at power up
- Goes off until serial communications are working
- Blinks on-off as data is received from GPS while waiting for Satellite signal lock
- LED is on solid once output is enabled
Fits into Aluminum Project Box Enclosure DIY 100*76*35mm - ebay search
External GPS Antenna with SMA connector
Inspired by Scullcom design

CPU choices are
- QT Py (SAMD based)
  - Adafruit QT Py SAMD21 Product Page
  - Seeeduino XIAO
  - 48 MHz
- QT Py (RP2040 based)
- XIAO ESP32C3
  - SeeedStudio XIAO ESP32C3 (New 2022-07)
  - RISC-V Single Core
  - Up to 160 MHz
  - 400 KB SRAM
  - 4 MB Flash
  - 2.4GHz Wi-Fi subsystem
  - Wiki
  - ESP32C3 Datasheet
Connectors/Headers
- DC Power
- AD0 GVS
- AD1 GVS
- AD2 GVS
- AD3 GVS
- I2C with ground/VCC
- TX/RX with ground/VCC
- SPI with ground/VCC
QTPy49 can be powered from with either the USB C or DC jack
- Automatic Schottky diode power switching between
  - 5V from USB C
  - 5V on external DC jack
  - 7-12V on DC jack
49x49mm ODAS form factor
(4) 4-40 mounting holes

GPS Satellite Positioning Module NEO7M UBLOX Module
- EBay search for NEO7M
Specifications:
Working Voltage: 3.3v-5.0v
Color: As Picture Shown
Description:
With micro USB interface, you can debug GPS module with ordinary phone data cable, no longer need to use USB-TTL and other tools.
TTL interface is reserved to facilitate the use of USB-TTL or external microcontroller to control and receive GPS information.
Ceramic antenna on module board, no GPS external antenna can be used to search for stars.
Reserved SMA antenna interface, can use external antenna, star search ability is stronger.

Previous design used modified PulseGen card to drive 50 Ohms at 3.3V level output
- Remove oscillator circuit parts (R/C)
- Only 1 BNC high quality (Amphenol) connector
- Wire from GPS PPS pin attached as below
- Use 1x2 pin header for power instead of 5MM Terminal Blocks

Signal	From	To	Color
GND	QTPy49 J4-1	GPS pin 4	Black
VCC	QTPy49 J4-2	GPS pin 5	Red
QTPy>GPS	QTPy49 J4-3	GPS pin 2	Blue
GPS>QTPy	QTPy49 J4-4	GPS pin 3	White
GND	QTPy49 J5-1	DRIVE50 J1-3 GND	Black
VCC	QTPy49 J5-2	DRIVE50 J1-2 VCC	Red
PPS	GPU pin 1	DRIVE50 J1-1 In	Purple
LED-VCC	QTPy49 J9-3	D0	Red
LED-GND	QTPy49 J9-1	GND	Black

Code runs on multiple CPUs on QTPy49
- QT Py (SAMD based) or
  - SeeedStudio XIAO or
  - Adafruit QT Py
- QT_Py_(RP2040_based)
  - SeeedStudio XIAO
  - Adafruit QT Py
FreqStdCap.ino - Tool that runs on Arduino to generate frequency bytestrings to send to GPS
GPS_004.py - Final working code
- Saved as code.py to auto-run
GPS_003.py - Capture data from GPS module a line at a time - helpful for debugging
GPS_002.py - Read 32 bytes at a time
GPS_001.py - Formatted stings output