Intro to the AVI-TAR User interface, Mk 1

In the last post I showed a profile shot of the AVI-TAR. I'll fill in some of the details in this post.

Visual Interface:

I tinkered with a few different display types before settling on a PCD8544 type screen. It's an 84x48 pixel LCD with LED backlighting. For now, I have it in a basic angled housing that sits on a replacement rail. Here's an operator's view:

(Don't mind the rough edges...prototype 3D printed plastics FTW!)

When powered up with no magazine inserted, you'll see this home screen:

The parts are:

• Upper left corner: battery voltage/status
• Middle left (purple outline): burst setting - right now in "safe" mode
• Lower left (green outline): round counter
• Center (red outline): magazine bar graph (empty right now - no mag inserted)
• Upper right (no outline): status messages
• Middle right (blue outline): rounds remaining in magazine
• Lower right (inverted text): selected magazine capacity

With a new magazine inserted:

I'm in 3-round burst mode with a full 100 round mag, ready to engage.

In addition to the home screen there are menus, some simple, some more complex, for setting modes, magazine sizes, viewing counters, etc. etc. More on that later. The settings are all controlled through a navigation rocker on the bottom of the hand grip:

If you've ever seen an S&T TAR-21, you'll wonder why that bottom cap is removable. I did, anyway. You really can't store anything in the hand grip since it's hollow all the way up into the main body cavity and you need a screwdriver to remove it in any case so it's not very practical in the field. I printed up this part as a replacement. Note the spherical depression that the switch sits in...keeps it from getting manipulated or damaged when the bottom of the grip drags or drops. 

The switch is a 3-position rocker (up, down and push-to-click) so you can have both hands on the gun and tucked in while you change burst settings, for example. My original idea was to put membrane switches on the side of the top rail. That's a no-go because you have to take your hand off the grip to push buttons AND which ever side you pick you're going to piss off opposite-handers. 

That was a fun bit of CAD work that took 5 versions to get right. I'm brand new to 3D printing, BTW, and if you've got any mechanical talent it's pretty simple to pick up. There's plenty of good free 3D CAD programs out there to play with. Dive in and make a mess the first few times...nobody will care and you'll learn quickly what works.

Next post I'll dive into the electronics. They're pretty simple and modern half-bridge motor driver ICs make the power side almost child's play.

Welcome to the AVI-TAR Blog!

AVI-TAR ("avatar") stands for "Advanced Visual Interface - TAR". It is a proof-of-concept Airsoft rifle built on an S&T (now imported by Umarex) ISI TAR-21 AEG. It's meant to look a little like a Halo DMR (maybe) and provides AEG features I've not seen in one package until now.

This project was launched about 7 months after I bought an S&T ISI TAR-21 "Explorer" AEG. It's a great platform out of the box and I've had only a few small problems with it, mainly in the fire selector group. There are some details to tuning the stock gun that I'll save for a later post, but if you put just a little time into it (and just a few bucks) you can get a high rate-of-fire, LiPo capable gun shooting 400fps all day long.

For all that, the gun felt "unfinished" to me. With the TAR all tuned up it's too easy to get trigger-happy and just firehose BB's down the field. After going through 5 300+ round mags in one 20 minute match, I decided to try some sort of "burst wizard" type gizmo. I tried 2 different ones. Yeah, they work, sort of, but they're not always accurate and programming can be fussy. Also, there's not much room in the TAR's battery compartment so plugging your usual "in-line" device in between your battery and the gun's wiring was a PITA. "If'n I'm gonna hack up my gun wiring, why not go whole hog", was my beer-driven thought one evening. 

Pro-tip: if you start thinking about how to build an iPhone into your gun you've had too much beer.

That's the genesis. I started with a blank sheet of paper and asked myself what I wanted:

• Burst firing control (1-9 and infinite auto)
• Battery monitoring with low voltage lock-out. I run LiPo packs.
• Positive detection of rounds expended, because
• Magazine size simulation and round counting
• A nice display that integrates into the TAR-21 design
• Simple user interface that doesn't require too much attention
• Easy to manufacture in quantity (if it ever comes to that)

After months of part-time (this is a hobby) design and development work, I present:

Doesn't look too different from a normal TAR-21, does it? It had it's first field trial on Memorial Day, out at Code Red Airsoft Park. It was largely a success; there are a few bugs to chase and some UX improvements to be tried. I was able to run over 2000 rounds through it before my battery dumped.

I'll start filling in the technical story soon, but for now here's an overview of the engineering:

• Arduino powered (Sparkfun's Pro Micro 16MHz/5V board)
• BTN7960B half-bridge motor driver
• "Nokia 5110" type LCD screen
• IR through-barrel interrupter-style round detection
• Multi-position switch for user interface mounted on handgrip
• "Magazine inserted" detector

Additional parts 3-D printed in black ABS (for now).

More pictures and some videos to come. Until then, "shoot and scoot"!