Build instructions: altimeter.kicad_sch
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1. Place the Seeeduino XIAO (XIAO-SAMD21-SMD, ref U1) straddling the
   trench, with its leftmost pin in hole a5. It also connects to the
   power (+) and ground (-) rails.
   [https://www.google.com/search?q=XIAO-SAMD21-SMD%20datasheet]
2. Place the Micro SD Card Module (TRANSFLASH, ref U3) straddling the
   trench, with its leftmost pin in hole a19. It also connects to the
   power (+) and ground (-) rails.
   [https://www.google.com/search?q=TRANSFLASH%20datasheet]
3. Place the BMP280_KK (BME280, ref U2) straddling the trench, with
   its leftmost pin in hole a31. It also connects to the power (+) and
   ground (-) rails.
   [https://www.google.com/search?q=BME280%20datasheet]
4. Insert the LiPo 3.7V 250mAh Battery_Cell (BT1): one lead into hole
   m11, the other into hole p12.
   [https://www.google.com/search?q=Battery_Cell%20datasheet]
5. Connect a jumper wire from hole m22 to hole c31 (net GND).
6. Connect a jumper wire from hole n22 to hole p11 (net GND).
7. Connect a jumper wire from hole b5 to hole b19 (net Net-CS).
8. Connect a jumper wire from hole l9 to hole b21 (net Net-MISO).
9. Connect a jumper wire from hole l10 to hole b20 (net Net-MOSI).
10. Connect a jumper wire from hole b8 to hole l23 (net Net-SCK).
11. Connect a jumper wire from hole b7 to hole b32 (net Net-SCL).
12. Connect a jumper wire from hole b6 to hole l33 (net Net-SDA).
13. Connect a jumper wire from hole m12 to hole m24 (net VBUS).
14. Connect a jumper wire from hole n12 to hole m34 (net VBUS).
