Add notes on part selection

BOM.md

@@ -9,16 +9,62 @@ This is a list of every part needed to assemble one Tangara.
 | Touchwheel cover (0.6mm FR4)  | See `touchwheel-cover`     |
 | 15 pos 0.5mm pitch FFC cable  | Samtec FJH-15-R-03.00-4    |
 | 4x 6mm M2 standoffs           | Wurth 970060244            |
-| 4x 14mm countersunk M2 screws |	                           |
-| 4x 8mm countersunk M2 screws  |	                           |
+| 4x 14mm countersunk M2 screws |	Accu SHK-M2-14-V2-A2       |
+| 4x 8mm countersunk M2 screws  |	Accu SHK-M2-8-V2-A4        |
 | Case top half                 | See `case-v2`              |
 | Case bottom half              | See `case-v2`              |
 | Switch cover                  | See `case-v2`              |
 | 2x Button covers              | See `case-v2`              |
 | SD card cover                 | TBD                        |
 | 3-pin 2200mAh 604560 LiPo     | EcoCell LIP2-001           |
+| Haptic motor                  | TBD                        |
 
 We're currently finalising our production v2 case design, including the SD card
 cover. Full sources for these will be available once they're finished.
 
-For the battery, note that a 2-pin cell may be compatible if R1 on the mainboard PCB is populated with a 10k 0603 resitor. We recommend sourcing a suitable battery locally, as international shipping of LiPo batteries can be difficult.
+Notes on selecting alternatives for specific parts are given below.
+
+## Display
+
+The display is considered a part of the faceplate, but there's enough options
+for sourcing that it's worth a few notes here.
+
+ - For production, we're using ER-TFT018-4 from EastRising Technology Co.
+ - [Adafruit's JFT-1800](https://www.adafruit.com/product/618) panel should also work fine.
+ - Most ST7735R / ST7735S displays available on AliExpress should work fine.
+
+## FFC Cable
+
+For all current mainboard and faceplate revisions, we use an FFC connector with
+tin plated contacts. You should therefore try to pick an FFC cable that has tin
+plated contacts, to avoid corrosion.
+
+Aside from the Samtec cable listed about, you might also consider:
+
+ - Molex 98266-0836
+ - GCT 05-15-D-0076-A-4-06-4-T
+
+## Screws
+
+Any 14mm and 8mm countersunk M2 screws will be fine. We've used Torx head for
+our production units because we're big nerds, but you can often find hex and
+Phillips head screws easily from local suppliers.
+
+## Battery
+
+For the battery, note that a 2-pin cell may be compatible if R1 on the
+mainboard PCB is populated with a 10k 0603 resitor. We recommend sourcing a
+suitable battery locally, as international shipping of LiPo batteries can be
+difficult.
+
+## Haptics
+
+Tangara's haptic motor driver supports both LRA (closed and open-loop) and ERM
+haptic motors, so sourcing a compatible motor is very easy. We'll update this
+BOM once we've locked in our production motor, but some compatible choices are:
+
+ - Vybronics Inc. VG0832022D (LRA)
+ - Vybronics Inc. VC1034B018F (ERM)
+ - Adafruit 1201 (ERM)
+ - DFRobot FIT0774 (ERM)
+