August 20th

Today I decided to choose a gps/gnss module or a chip.
Turns out that standard gnss has precision of 3-10m so it is what I need

Turns out that there are bunch of sattelite systems.

Reading a bit I chose the SAM-M10Q module since it is a low-cost gnss module which incorporates built-in chip, circuitry, and antenna.

Then I started reading datasheet of ht-ct62 and then sx1262.

Also I then checked the firmware for ht-ct62. Thank God it was available.

For the display I chose ssd1306 since it is a low-cost OLED display module.

Since I do want to have a 18650 battery power supply, I need to have a buck boost converter that can step up and step down the voltage.

So the whole thing would be something like this:

flowchart TD
    USB["USB-C <br/> 5 V"] --> CHG["BQ24074RGTR <br/> charger"]
    BAT["18650 battery<br/> 3.0–4.2 V"] --> CHG
    CHG --> SYS["SYS <br/> 3.0–4.5 V"]
    SYS --> BB["TPS63001 <br/> buck-boost converter"]
    BB --> RAIL["3.3 V rail"]
    RAIL --> MAIN["HT-CT62 + OLED"]
    RAIL --> LOAD["TPS22917 <br/> load switch"]
    LOAD --> GPS["SAM-M10Q <br/> GPS module"]

I then set up the usb_c and charging IC bq24074gtr.

For setting up the charging IC I followed this logic
EN1 and EN2 configuration

EN2 = 0
EN1 = 1

Which places the charger in USB 500 mA input-limit mode:

EN2 EN1 Mode
0 0 100 mA USB
0 1 500 mA USB
1 0 Current set by ILIM resistor
1 1 Standby

For the buck boost converter it has to be pretty much like datasheet except for PS/SYNC.

It controls the operating mode

• PS/SYNC state Mode
• LOW/GND Power-save mode enabled
• HIGH Power-save disabled; forced fixed-frequency operation
• Clock signal Synchronizes switching to an external clock

So in this session I:

• Researched additional components
• Chose to add SAM-M10Q GPS module, SSD1306 oled, BQ24074RGTR battery charger, and TPS63001 buck-boost converter
• Read the datasheets for each component
• Started the schematic

Next steps:

• Continue schematic
• Review the schematic and make any necessary changes