MicroBoSL
Here we will document the design of the microBoSL board , a miniaturized version of the BoSL board.
Key changes from the BoSL board to the microBoSL board:
- Upgrade SIM7000 to smaller SIM7090
- Remove much of the connectivity to achieve smaller profile
- Add NFC
- Make board much smaller. No more than 30 mm in width.
- Removed MS5803
To do this many components will have their parts changed to a smaller footprint version.
These substitutions include:
- Many passives -> mostly 0603
- ATmega328P-AU -> ATmega328P-MMH
- FT232RL -> FT232RQ
- 74HC126D -> 74HC126PW-Q100
- MCP7940NT-I/SN -> MCP7940NT-I/MNY
- MCP1700-3302E_SOT89 -> MCP1700-3302E_SOT23
20th January 2020
The micro BoSL is here:
MicroBoSL Front
A quick test reveals that programs are able to be uploaded to the device. This verifies the status of the MCU and the USB-TTL converter.
Next is to test the RTC. A quick test with indicates that this too is working well. An issue is had a bit with the LEDs. These tend to stay on even after the USB power is removed. This is an issue as it could cause extended power draw. A work around found was to hold the reset button for 3 seconds until all the LEDs turned off after this they did not seem to turn on again.
A test using the RTC persistence time keeping indicates that the board can operate on battery power hence, the o-ring and power delivery circuit does indeed work.
Now we need to test the MOSFET.
