[doc] Add Schematic

[bovi]

Add schematics of MindDot

The following items should be integrated into the schematic:

• esp32c3
• lis2dh
• hx6306p332mr
• ath10
• push-button
• programming circuit
• voltage measurement
• review

Review feedback:

• V_in adjustment for lower power consumption
• connect INT2 of LIS2DH
• ATH10 second I2C bus?
• bootstrapping pins to be re-considered and not used for other stuff
• un-used pins to pin-header for debugging
• optional LED

[bovi]

first schematic version checked in under: 7d61a6e

[bovi]

push button, programming circuit fix and voltage measurement implemented under: 90db984

[bovi]

Review suggestions:

• R4 and R5 seem to be there in order to measure V_in. I suggest to make the values a little bit higher, in order to reduce the power consumption a bit. In the schematic, there would be more than 1mA continuously flowing through those resistors. Maybe 100k & 200k would be better?
• If we are short of IOs, it’s okay to leave INT2 of LIS2DH unconnected, but if we still have IOs free, we could also connect it.
• On page 8 of the AHT10 datasheet it says that the AHT10 can not be on the same i2c bus with other devices. Unless I am reading the datasheet wrong, we would have to create two i2c busses.
• According to the ESP datasheet, IO2, IO8 and IO9 are used for bootstrapping during boot, so I think we probably cannot use them in the way it’s done in the schematic. (See the section “Strapping Pins” in the datasheet.)
• I suggest to lead unused IOs to some pinheader pads so that we can easily access them, e.g.. for debugging purposes.
• An optional LED on one of the IOs might be nice.