Matt's RV-7 Project

I ran the 6 AWG wire that provides power to the main bus up from the current limiter, through the firewall, and across the cockpit to the main fuse block. This wire is clamped to the engine mount in three places, since it will form the spine of a whole bundle of wires that will run up and down the starboard side of the engine compartment.

This was the first outing for my latest tool, a pair of vise grip pliers modified to hold adel clamps in position while you get the bolt in. Normally these are a giant pain to install, but the tool helped. I did find that I still needed to use the safety wire trick sometimes, which in conjunction with the pliers made installing adel clamps a relative breeze.

Closeup view of the bottom end of the wire, where it attaches to the current limiter:

Up the side of the engine mount and through the firewall passthrough:

Inside the cockpit it takes a turn, goes through the subpanel ribs via a pair of snap bushings, takes another 90 degree bend into an adel clamp, and penetrates the subpanel through another snap bushing.

From there it dips down, and will eventually attach to the post on the main fuse block as soon as I can scare up the proper ring terminal for the end.

I also made some fusible links, which are visible in the picture above. These will be used to protect the wires that go from the two fuse blocks to the diode on the other side of the subpanel. They're just lengths of normal tefzel wire, four sizes down from the wire being protected (the wires to the diode are 10 gauge, so these links are 14 gauge). Over the wire is a fireproof silicone sleeve, in case the fusible link is called upon to do its thing. The idea here is that you use a fusible link anywhere you can't normally use a regular fuse or circuit breaker, but where you still want protection in the unlikely event of a short circuit.

Not a lot of work on the plane lately due to too much time spent at the office, too much heat in the garage, and too much Mary away on the road (which you'd think would theoretically leave more time to work on the plane, but in reality I seem to always find myself at work instead). But this was a pretty good weekend.

I got my annunciator controller board back from ExpressPCB. Their board layout software is pretty terrible, but the finished product looks okay. If you look closely, you might be able to spot the switch mounting pad I had to grind off because it was too close to the processor reset line. A real board layout tool would have caught that with a design rule check, but of course the crappy free software doesn't have one. Oh well – that turned out to be the only mistake I made (and believe me, nobody is more surprised than I am).

I grabbed a spare D-sub connector and made a little test harness to power the board and test its inputs and outputs.

In keeping with the time-honored traditions of testing out a new PCB design, I soldered the minimal components needed to get the processor running (power supply, oscillator, and the microcontroller itself) and hooked it up to the debugger to see if I could make it blink an LED.

It blinks! This means that the microcontroller is alive and can be programmed. It doesn't look like much, but if a board can get to this stage, then almost everything is working.

Here's the finished product, with voltage dividers, filters, and driver transistors in place. It will be able to sense up to 8 inputs and control up to 6 annunciator lights, depending on how I choose to write the finished firmware. The end goal here is to be able to do a few things with warning lights that are just slightly more sophisticated than simply hooking up a lamp.

I bought a copy of DeltaCad and spent the weekend teaching myself to use it well enough to create a design for my instrument panel. Unfortunately I can't put a picture of it here for reasons not worth going into. But it's pretty cool.

Your humble author apologizes for the lack of blog-updating. Working sixty hour weeks is incompatible with airplane building! Also, the garage is a furnace this month. However, I did manage to sneak in some time this weekend playing with electronics. I'm designing an annunciator light controller for the panel, which has turned out to be a fun way to exercise the very rusty hardware skills I haven't used since I became a full-time software weenie.

I soldered up a little microcontroller board I bought as a cheap mail-order parts kit:

Then I breadboarded a prototype circuit to verify that the basic design was sound. For this part I raided some old boxes of electronic junk I've been hauling around for at least a dozen years. You just never know when you'll need a 10uF cap on a Saturday night!

Then I spent an afternoon routing a little board. When I used to get paid to design PCBs, I had access to some pretty nice CAD tools. Not so much anymore – the free ExpressPCB software is much less capable, but I got the job done eventually. Next time I might try Eagle, but I think that all the free board layout tools pretty much suck in different ways.

I still haven't settled on the actual annunciator lights I want to use, but at least by next week I should have all the parts I need to make a board to control them.

I decided to mount the main and endurance bus fuse blocks on the left side of the subpanel, just behind where the pilot's displays will go. Access to the wiring should be pretty easy after removing one or more glass displays to gain access. Or, I will always be able to go the more uncomfortable route, up from the floor while lying on my back getting poked in the ribs by the fuel selector.

The essential bus diode (with hefty heatsink) is mounted to the other side of the subpanel. I tried to plan its location so that some of the screws used to mount it can also be used to attach adel clamps.

Mary came down to play Bejeweled on her phone and drink wine and watch me work. She composed and photographed this artful scene while I was preoccupied:

Would the isopropyl alcohol in the background count as a dry white? And which do you serve with pneumatic tools, anyway?