diff --git a/README.md b/README.md
index 3609bce..7dca6cf 100644
--- a/README.md
+++ b/README.md
@@ -48,6 +48,7 @@ This project is open source and available under the [AGPL-3.0 License](LICENSE).
 ## Documentation
 - [SFBus Protocol](software/pc_client/doc/sfbus-proto.md)
 - [Websockets Protocol](software/pc_client/doc/api-doc.md)
+- [BOM](cad/BOM_FlapUnit.md)
 
 ---
 ## Credits
diff --git a/cad/BOM_FlapUnit.md b/cad/BOM_FlapUnit.md
new file mode 100644
index 0000000..f62cdf7
--- /dev/null
+++ b/cad/BOM_FlapUnit.md
@@ -0,0 +1,113 @@
+# Bill of Material for 1U/2U Flap Unit
+
+## 3D Printed Parts 
+| part-number | part | file | amount | notes |
+| ----------- | ---- | ---- | ------ | ----- |
+| FU-001 | Unit Frame Base     | STL Unit/splitflap-unit-base.stl | 1 | common for all units |
+| FU-002 | Unit Frame Cover 1U | STL Unit/splitflap-cover-1u.stl  | 1 | only for 1U wide unit|
+| FU-003 | Unit Frame Cover 2U | STL Unit/splitflap-cover-2u.stl  | 1 | only for 2U wide unit|
+| FU-004 | Unit Drum Core      | STL Unit/splitflap-drum-core.stl | 1 | common for all units |
+| FU-005 | Unit Drum Core 1U   | STL Unit/splitflap-drum-outer-1u.stl | 1 | only for 1U wide unit|
+| FU-006 | Unit Drum Core 2U   | STL Unit/splitflap-drum-outer-2u.stl | 1 | only for 2U wide unit|
+| FU-007 | Flaps   | ... | 45 | |
+- 49 Individual Parts per module
+
+## Hardware
+
+| part-number | part | amount | notes |
+| ----------- | ---- | ------ | ----- |
+| FU-011      | Ball Bearing 684ZZ (9 x 4 x 4mm) | 1 | |
+| FU-012      | Stepper 28BYJ-48 DC 12V | 1 |  **!! Use 12V Variant. NOT 5V !!**|
+| FU-013      | Heat insert M3 x 3mm | 3 | |
+| FU-014      | Heat insert M3 x 5mm | 4 | |
+| FU-015      | M3x5 Screw DIN 912 | 3 | |
+| FU-016      | M3x12 Screw DIN 912 | 2 | |
+| FU-017      | M3x8 Screw DIN EN ISO 10642 | 2 | |
+| FU-018      | Magnet round d=2mm | 1 | |
+- 17 Individual Parts per module
+
+## Electronics
+| part-number | part | amount | notes |
+| ----------- | ---- | ------ | ----- |
+| FU-031      | Module Controller PCB | 1 | |
+| FU-032      | ATmega8A-A | 1 | |
+| FU-033      | SN75176AP | 1 | |
+| FU-034      | ULN2003 | 1 | Can be salvaged from the driver board that usually comes with the stepper motor |
+| FU-035      | A1101xLH | 1 | SOT-23W variant! |
+| FU-036      | 16,0000-HC49U-S Crystal | 1 |  |
+| FU-037      | Capacitor 10u 35V (Radial_D6.3mm_P2.50mm) | 1 |  |
+| FU-038      | Capacitor 10u 16V (1206) | 1 |  |
+| FU-039      | Capacitor 22p (0805) | 2 |  |
+| FU-040      | Capacitor 100n (0805) | 4 |  |
+| FU-041      | Fuse 200mA (0805) | 1 |  |
+| FU-042      | JST B5B-XH-A | 1 |  |
+| FU-043      | Resistor 1k | 1 |  |
+| FU-044      | Resistor 10k | 3 |  |
+- 20 Individual Parts per module
+
+
+## Summary:
+Parts per module: 76 (mostly 3d printed)
+
+# Bill of Material for 4Unit Backplane
+
+## 3D Printed Parts 
+| part-number | part | file | amount | notes |
+| ----------- | ---- | ---- | ------ | ----- |
+| FP-001      | Upper Slot | STL Slot/splitflap-slot-upper.stl | 1 |  |
+| FP-002      | Lower Slot | STL Slot/splitflap-slot-lower.stl | 1 |  |
+- 2 Individual Parts per module
+
+## Sheet metal
+| part-number | part | file | amount | notes |
+| ----------- | ---- | ---- | ------ | ----- |
+| FP-003      | Backplane | Sheet Metal/sheet-metal-backplate.dxf | 1 |  |
+- 1 Individual Parts per module
+
+## Hardware
+| part-number | part | amount | notes |
+| ----------- | ---- | ------ | ----- |
+| FP-011      | Heat insert M4 x 5mm | 4 | |
+| FP-012      | Heat insert M3 x 5mm | 4 | |
+| FP-013      | M3x5 Screw DIN 912 | 8 | |
+| FP-014      | M4x10 Screw DIN 912 | 4 | |
+| FP-015      | M3x5 Standoff | 8 | |
+| FP-016      | M3 Nut | 4 | |
+- 32 Individual Parts per module
+
+## Electronics
+| part-number | part | amount | notes |
+| ----------- | ---- | ------ | ----- |
+| FU-031      | Backplane PCB | 1 | |
+| FU-032      | PhoenixContact_MSTBA_2,5_2-G-5,08 | 2 | |
+| FU-033      | Phoenix_MSTB:PhoenixContact_MSTBA_2,5_3-G-5,08 | 4 | |
+| FU-034      | L7805 | 1 |  |
+| FU-035      | 74AHCT1G125 | 1 | |
+| FU-036      | 2x08 Edge Connector | 4 |  |
+- 13 Individual Parts per module
+
+## Summary:
+Parts per assembly: 48 
+
+# Bill of Material for Backplane connection bracket
+## Sheet metal
+| part-number | part | file | amount | notes |
+| ----------- | ---- | ---- | ------ | ----- |
+| FC-001      | Bracket | sheet-metal-connector-middle.dxf | 1 |  |
+- 1 Individual Parts per module
+
+## Hardware
+| part-number | part | amount | notes |
+| ----------- | ---- | ------ | ----- |
+| FC-011      | M4x10 | 8 | |
+| FC-012      | M4 Nut | 8 | |
+- 16 Individual Parts per module
+
+## Summary:
+Parts per assembly: 17 
+
+# Parts for full display (12x3)
+- Display Units: 36 (2736 Parts)
+- Backplane Units: 9 (432 Parts)
+- Backplane Connectors: 12 (204 Parts)
+- Sum: 3372 Individual Parts