CarHUD Requirements

Since this is an Engineering blog, we're going to dive into requirements for the Phase 1 system.  It may be boring, but requirements detail your end design.

As a Systems Engineer, I do a lot of different things in my day job.

I'm assuming your mind went directly to the movie "Office Space.  The part where Tom Smykowski tells the consultants that he takes the specs from the customer and gives to the engineers is sort of a broad generalization of a Systems Engineers role.

I got lucky and was put into a position where I do a lot of integration and testing, but the main thing Systems Engineers do is Requirements capturing and verification.

Requirement Tiers

All requirements are derived from a single source, the Tier 1 document.  This is what would be provided by a customer.  In the case of the CarHUD, I'm my own customer and will be defining the high level system requirements.  The requirements in this document are written at a very high level.

Here are my Tier 1 requirements:

1. The CarHUD shall be based around a Raspberry Pi computer.
2. The CarHUD shall project information to the car windshield.
3. The CarHUD shall use consume less than 180W of power.
4. The CarHUD shall interface with the vehicle over OBD-II.

There are lots of rules about how requirements should be worded, but I'm not going to be strict with this project.  Depending upon your job, you may be required to follow rules with your requirements documents.

Why were these four requirement chosen for Tier 1?

1. I had a Raspberry Pi and was looking for a 
2. I need to define how the system will display information, where is it going to be shown.
3. Cars have a 12V battery and cigarette lighter sockets allow for 15A.  This will define the power consumption for all the system components.
4. This requirement tells us how we need to interface with the vehicle.

From here, we can start to flow down the Tier 1 requirements into more detailed requirements.

For the Tier 2 requirements, we'll break them out into sections:

HUD Controller:

1. The HUD Controller shall be programmed with an embedded version of Linux.
2. The HUD Controller shall use an ELM-327 based device for interfacing with the vehicle.
3. The HUD Controller shall use use the ELM-327 command set as tailored for the implementation required, specific features required for diagnostic purposes are not needed.
4. The HUD Controller application shall start upon boot of the computer.

Projector:

1. The projector system shall receive video over an RCA Component signal.
2. The projector system shall be powered by 12V.
3. The projector system shall be able to control brightness.

Power:

1. The HUD Controller shall consume no more than 1A at 5V.
2. The HUD Controller shall consume no more than 1A at 12V.
3. The projector system shall consume no more than 8A at 12V.

For more detailed projects, you'll have multiple Tiers of requirements.  For the CarHUD, there is no real need to delve into lower level requirements.