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Hardware Details and Mods

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pigrew edited this page Sep 5, 2017 · 4 revisions

BOM

  1. STM32 blue-pill board
  2. 0.96" 128x64 OLED, based on the SSD1306 chipset, which uses the chipset's internal DC-DC converter (code changes are required if you see an inductor on it)
  3. TruePosition GPSDO
  4. 0603-sized resistors: (1) 1.5kΩ resistor, and (2) between 1.5kΩ and 2.5kΩ (I'm using 2.2kΩ)
  5. (optional) 0402-sized 100nF decoupling capacitor for Vbat.
  6. Power sources
    1. 12Vdc for the TruePosition board (>= 1A, 2A suggested)
    2. 3.3Vdc or 5V for the controller/display
  7. RF connectors/cables
    1. SMB antenna connector
    2. MCX PPS/10MHz connectors

Modifications to blue-pill board

On the Blue-pill board, remove the existing USB pull-up, and replace it with a resistor between A15 and D+:

Also, cut the 5V track between the USB connector and the tee that goes to Vreg and the 5Vpin, so that the USB Vbus is isolated, and add a wire between B12 and VBUS (used to detect if the USB port is connected):

A third (optional) change is to provide power the the Vbat pin, as suggested by ST Micro. To make this change, add a jumper between VBAT and V33. Also, a 100 nF decoupling capacitor should be added close to the micro by scratching off the solder mask. I used a 0402 size cap, and some wirewrap wire. It would be easier to add wire between VBAT and V33 header pins.

Display Modifications

For the I2C display, replace the pull-ups (likely 10kΩ) with between 1.5kΩ and 2.5kΩ:

Connections

Power the board with either 3.3V using a V33 pin, or 4V-5.2V using a 5V pin. Power the OLED display using 3.3V from the blue-pill board.

Pin Usage
GND GND to Trueposition GND (pin 1 or 3)
PA2 TX to TruePosition UART (pin 2)
PA3 RX from TruePosition UART (pin 4)
(PA11) USB DN
(PA12) USB DP
(PA13) JTAG/SWDIO
(PA14) JTAG/SWCLK
(PA15) USB pull-up (1.5k to D+)
PB10 I2C SCL(use ~2.2k pullup)
PB11 I2C SDA (use ~2.2k pullup)
(PB12) USB VBus
(PC13) Blue pill LED
(PC14) 32 kHz crystal
(PC15) 32 kHz crystal
(PD0) 8 MHz crystal
(PD1) 8 MHz crystal
V33/V5 Input power to microcontroller board
V33 OLED power
GND OLED GND
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