AVI-TAR System Design Part 3: Parallel Tasks

See the Intro Video for a quick demo of the prototype

In the last post I talked about the "bench test" system. This post is about the process behind building an integrated prototype.

After the Bench Test...

So I have a functional hardware and software system literally duct-taped to my AEG. The next step has to be mechanical integration, right? (Yes, that's rhetorical.)

I broke it down into these parts:

• logic board location and internal wiring
• display location and housing
• scroll switch location and housing
• Magazine switch mounting

I'd already kludged the IR detector and will be revisiting that subsystem later on. Each of these parts stand alone and so I worked on them in parallel. We'll start with the heart of the system here.

Logic Board

From the start I'd had the idea of mounting the logic on the underside of the top rail assembly of the TAR-21. It's a long plastic part that slides out of the main body and it has a lot of dead space. The original board I'd designed was the approximate shape but not quite right. Also, since it used .1" headers for most connections it was not field-ready. Those headers are big and do not lock the connectors in place. Great for tinkering, not so much for real world use.

So, back to Eagle Lite for some tweaks to the schematic and board layout. The schematic needed some cleanup, inserting the IR detector connections and deleting some now unneeded parts. Here's the REV B schematic:

As you can see from this version, I'm learning a little more about schematic-building.

A not so quick trip through the board layout and I get this, which went off to OSH PARK for manufacture:

You'll notice that I'm using through-hole components for everything but the half-bridge power device. It's easier for me to build and troubleshoot and I don't need to shrink the board down any further.

Here's the board stuffed and mounted into the top rail. It's a friction fit but there are provisions for fasteners.

I'm using Hirose connectors for the low-power connections. I'm here to tell you that terminating the wires into those without the specific crimping tool is a good way to determine how motivated you are in your work. It's tough, fiddly work.

Next time...the display housing.