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STM32G474VET6STMicroelectronics
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SI5351C-B-GMSkyworks Solutions, Inc.
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SP3232EEN-LMaxLinear
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25 MHz crystalKYOCERA
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SP3232MaxLinear
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STM32CubeIDE |
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U-Center 2u-blox
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ClockBuilderSkyWorks
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GPSDO STM32G474 NEO-M8N
New GPSDO concept.
No any PLL loops or frequiency regulations.
Maximum stability and accurancy theoreticaly avalable.
Everyting is made in GPS receiver itself.
Theory:
- GPS receiver have its internal 48 MHz TCXO, directly locked to satellites signals.
- Receiver is reprogrammed to output on it's TIME_PULSE output not one pulse per second, but 24MHz signal (48MHz divided by 2).
- This signal is used as an external OSC_IN of MCU STM32 -> time base (all timers, pulses and clocks) of MCU will be accurate to GPS timings.
- STM32 outputs this frequency on its MCO (Master Clock Output).
- MCO is connected directly to CLKIN (Clock In) of Skyworks si5351C syntezier.
- MCU STM32 is used only for service functions and programming si5351C output multisync dividers and drivers.
- To achive better accurancy firmware of STM32 put receiver in "stationary" mode - it wil not resolve navigation solution, only timing.
No any regulations of si5351C is needed. It is clocked directly from GPS receiver internal TCXO reference 24Mhz signal. All output frequiencies are digitaly mathematecaly calculated without any analog or temperature drift.
We have 8 independent si5351 outputs (1-200MHz) directly clocked from receiver reference frequiency.
Frequiency stability of all si5351 outputs == receiver internal stability and accurancy. No any PLL or FLL loops are needed.
ublox NEO-M8N is a multisystem GNSS module wich can work with GPS, Galileo, GLONASS, BeiDou, IMES and QZSS satellite contallations.
Development board is equiped with female headers for connecting 2.8" Sitronix ST7789 TFT-LCD display with touch screen and SD card reader onboard.
And MaxLinear SP3232 TTL<-> RS232 level converter for output NMEA text data to tranciever, for example ICOM IC-9700.
You are invited to become a beta tester of this project or write your own sofware.
GPSDO STM32G474 NEO-M8N
*PCBWay community is a sharing platform. We are not responsible for any design issues and parameter issues (board thickness, surface finish, etc.) you choose.
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I'v added a photo from 1'st test prototype run.
This is UBX protocol message to switch ublox receiver to output 24MHz on TIME_PULSE pin: // TP5(Timepulse5) - TIME_PULSE - 24 MHz Message[ 0] = 0xB5; Message[ 1] = 0x62; Message[ 2] = 0x06; Message[ 3] = 0x31; Message[ 4] = 0x20; Message[ 5] = 0x00; Message[ 6] = 0x00; Message[ 7] = 0x01; Message[ 8] = 0x00; Message[ 9] = 0x00; Message[10] = 0x00; Message[11] = 0x00; Message[12] = 0x00; Message[13] = 0x00; Message[14] = 0x00; Message[15] = 0x36; Message[16] = 0x6E; Message[17] = 0x01; Message[18] = 0x00; Message[19] = 0x36; Message[20] = 0x6E; Message[21] = 0x01; Message[22] = 0x00; Message[23] = 0x00; Message[24] = 0x00; Message[25] = 0x80; Message[26] = 0x00; Message[27] = 0x00; Message[28] = 0x00; Message[29] = 0x80; Message[30] = 0x00; Message[31] = 0x00; Message[32] = 0x00; Message[33] = 0x00; Message[34] = 0x6F; Message[35] = 0x00; Message[36] = 0x00; Message[37] = 0x00; Message[38] = 0x11; Message[39] = 0xD8; Message[40] = 0xB5; Message[41] = 0x62; Message[42] = 0x06; Message[43] = 0x31; Message[44] = 0x01; Message[45] = 0x00; Message[46] = 0x00; Message[47] = 0x38; Message[48] = 0xE5; HAL_UART_Transmit(&huart2, Message, 49, 50);