Based on my experience with the first version, I've made an update of the schematics and the v2 of the PCB is now ordered. Here is the list of changes:
- Additional filtering capacitors for STM (one per each pair of VSS/VDD(A) inputs as per datasheet) and for the LCD (according to LS027B7DH01 datasheet).
- Tantalum capacitor (220 uF) in parallel to the battery to avoid voltage drops during heavy processor activity when the battery is weak.
- Power pin on ST-Link header to power the calculator while flashing or to measure current consumption. Two Schottky diodes as a protection when both ST-Link and battery power is on, and to protect from reverse battery polarity.
- New battery holder (Keystone 1057) which sits in the cutout of the PCB to reduce thickness of the enclosure.
- Improved PCB layout for TPS61222 voltage booster (following datasheet)
- More compact PCB (126x64 mm) with screw holes and cutout for LCD flat cable.