Simplify Database ER Diagram/Schema

Question

For a school project, we have to create our own database. I decided to create a database to manage my electronic component inventory. As a requirement, we needed to create an ER diagram, then from that diagram derive the database schema. Unfortunately for me, the professor believes that the diagram I created can be simplified and the "Part" entity is unnecessary.

This is the diagram I came up with, and here is the derived schema.

If I remove the Part entity, then in order for a Circuit entity to "use" any number of any part, and have each part associated with possibly any circuit, I would have to have a separate M-to-N relationship from each component type to Circuit. Each of those relationships would generate a new table. This would definitely go over the strict maximum number of tables we are allowed for the project.

If the professor specifically mentioned Part was unnecessary, then there must be some way to remove it that results in a simpler ER diagram and schema - but I can't see what it is.

Maybe you guys can see what it is and give me a hint?

EDIT: Dan W had a great suggestion. I could eliminate the Part by giving each part type (Capacitor, Resistor, etc.) their own keys. Then inside of uses part, include foreign keys to those components. I would have to assume that each entry of the table would only be associated with a single part, the rest being null. Here's the resulting schema. This schema should work well. But now I have to figure out exactly what modifications to the ER diagram would correspond to this schema.

EDIT2: I've come to the conclusion that the relationship I'm looking for is n-ary. According to several sources, to convert from the n-ary to a schema you include the primary key of each participating entity type's relation as foreign key. Then add the simple attributes. This is what I came up with.

Answer 1

You have a strict maximum number of tables (physical design) but are you restricted in your ER diagram to that number of entities (logical design)? All of your entities for parts - resistors, transistors, capacitors, and General IC - could be stored in one parts table with all the attributes of Part, resistors, transistors, capacitors and General IC as nullable columns. If an attribute is valid for all types then it is not nullable. Include another column in the parts table which identifies the type of part (resistor, transistor, capacitor or IC) although you already have a type column in all the entities which might also serve for this.

The Parts table in your schema is now:

PartID (PK)
Quantity
Drawer
Part Type
Value
Tolerance
Subtype
Power Rating
Voltage
Term_Style
Diam
Height
Lead_Space
Name
Case
Polarity
Use
V_CE
P_D
I_C
H_FE
Package
Pins
Description

and you drop the Resistor, Capacitor, Transistor and General IC tables in your schema. Leave those entities in your ER diagram because that shows which attributes in the Parts table is required (shouldn't be null) for each part type.