I always thought it would be cool if we counted time in units that were multiples of ten of each other. This is known as decimal time. There'd be 100 seconds in a minute, 100 minutes in an hour, and ten hours in day. A recent Twitter conversation got me thinking about this again.

The problem with this idea is that it requires the second to be redefined. To be sure, there are other problems, too, like how do you convince six billion people to change their notion of what seconds, minutes, and hours are?

But changing the length of a second means changing a lot of scientific constants, and that's a pretty serious undertaking. It would be better to start with the existing unit of a second (which, incidentally, is a metric unit), and build on top of that.

So, let's put aside the actual labels we'll give each of these units, and let's keep a second a second. Now let's put 100 seconds in a minute, 100 minutes in an hour, and that gives us 8.64 hours in a day. That's not a very nice, round number. How important is it that it be a "nice" number, though?

On Earth, the average day is 86,400 seconds long. On Mars, the average day (sol) is 88,775 seconds. In our decimal time units, that would be 8.86 hours. On Earth's moon, a day is 2,551,443 seconds long, or 255.1 hours (are you starting to see the advantage of decimal time?). Obviously, as our species spreads out to other celestial bodies, having an even number of hours in the day everywhere will impossible, because not all days will be the same duration.

So, let's compare some other durations:

Yuck! The problem with decimal time based on the existing second is that there are no conveniently-sized units for most day-to-day human activity.

The quarter-hour, or 15 minutes, is 900 seconds. That's nearly 1000 seconds, so perhaps the kilosecond would be a convenient unit. Ten kiloseconds would be a little over 2 h 45 m traditional, so maybe we're on to something here.

I've rounded the kilosecond times for the activities, because their durations aren't very precise to begin with. It seems like the kilosecond could be a fairly convenient unit, after all.

Now we just need to find good names for these decimal units. Seconds are fine, but the rest need new names that are easy to say, abbreviate acceptably to unit labels, and don't sound cheesy (the old Battlestar Galactica used "centons," and I never did figure out how much time that represented).

We might also ponder how one writes decimal time. Traditionally, in the U.S. and other parts of the world (but definitely not all!), a time of day (or duration) is written as double-digit numerals separated by colons: 12:37:58. Decimal time can be written much more simply, as decimal hours in the day: 4.548. Now, imagine you want to add (in traditional units) 4 minutes and 22 seconds to 12:37:58. Try it. It sucks. But adding 262 seconds to 4.548 decimal hours is much easier: 4.548 h + 0.0262 h = 4.574 h.

It may seem weird, but if you grow up with these units, and everything around you uses them, they'd be obvious, and the units we use today would seem strange.

Sources

Metric time. (2011, February 17). In Wikipedia, The Free Encyclopedia. Retrieved 05:51, March 27, 2011, from http://en.wikipedia.org/w/index.php?title=Metric_time&oldid=414432996

Timekeeping on Mars. (2011, January 15). In Wikipedia, The Free Encyclopedia. Retrieved 05:52, March 27, 2011, from http://en.wikipedia.org/w/index.php?title=Timekeeping_on_Mars&oldid=408111863.

Lunar day. (2011, March 17). In Wikipedia, The Free Encyclopedia. Retrieved 05:53, March 27, 2011, from http://en.wikipedia.org/w/index.php?title=Lunar_day&oldid=419235268.

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The last 24 hours have been an exercise in frustration, sleeplessness, wrong turns, dead ends, and embarrassment. I've been working on a little project that developed a problem, seemingly inexplicably, and I could not find the cause.

This little AVR-based project includes a 16x2 character LCD display. For the last week, it has been working like a champ. I got a lot of fundamentals worked out, and decided to start cleaning up the code. It had gotten to be quite a mess, as I quickly worked through the various building blocks of the overall device, and I needed to make it look more like the final product would.

I would make small changes, compile them and load them onto the device, making sure things worked, or worked the way I wanted them to. Suddenly, the LCD stopped working. I could tell the MCU was doing its job, as the heartbeat LED kept blinking, and I was getting debugging output from the serial console attached. But no LCD.

Since the last change I made was to add a MOSFET so that I could power down the LCD when not in use, I thought perhaps I had damaged the LCD. I removed the new circuitry, and spent some time searching for a similar LCD to try. Found one, popped it in, and it behaved the same way!

Perhaps I had damaged the MCU. Unlikely, because everything else was working perfectly. So I replaced that, flashed it, and tried again. No dice. Now, I was already operating on very little sleep this weekend, and it was after midnight. Had I been firing on all cylinders, I would've abandoned the effort and gone to bed. Or had looked for a software problem first. But I had been on such a roll, and I don't back down easily from a challenge like this.

I fired up the oscilloscope and started probing the connections between the MCU and LCD. They were one of the first things I had checked, making sure everything was still connected. Since I had tried the new MCU with the old LCD, I thought maybe it was damaging the MCU pin drivers. So I checked each one to see if it was changing state.

I found five that weren't! I pored over the code, thinking somewhere I had introduced a change (by accident), that disabled some of the pins. I couldn't find anything. I tried a third MCU. I tried a third LCD. Nothing. Same five pins not working. Then I realized that there must be an internal peripheral on those pins inside the MCU that was overriding the general I/O functionality. Looking at the data sheet, I saw that the JTAG interface lived on those pins, and a vague memory floated up: new MCUs have the JTAG enabled by default.

So, I disabled that, excited that I had figured things out, and tried again.

No luck. Still didn't work. Argghhhhhh!

I gave up. Went to bed (now well past 2 am), got up late the next morning, went to work, came home. Watched an hour of TV, then came in here to figure out the problem.

I decided to revert my source code back to a known-working revision. I was currently on revision 15, and the checkin comments showed the LCD had started working after r7. So, I updated my code to that revision, and tried it. It worked! Praise jeebus!

I tried to see the differences between that code and the latest, but there were too many changes. I updated to the latest code and tried again, just to verify the problem was in the code, and it still worked! WTF? Now, somewhere in here I had made a couple other changes to the code, trying to undo the most recent additions. The latest code had those changes (I had checked them in before reverting), so I was really confused.

But sure enough, it seemed to work. So I put back the code I had just taken out, to try to reproduce the problem. It still worked. WTH? (Ironically, I was now looking for failure, because that would tell me I had figured out the "root cause," as NASA likes to put it.) I could not reproduce the problem.

So, I cleaned up the recent experimentation, checked in the code, and set about to do new work. I wanted to measure the current consumption in various operating modes, so I wired in the ammeter.

Suddenly, the problem reappeared. Argghhhhhh!

I started to think that I wasn't giving the LCD sufficient voltage. The prototype design had a diode from the Vcc to the rest of the circuit, and I thought maybe that little voltage drop was enough to cause problems. That didn't really explain why it had been so reliable up until now, or why it was so unpredictable. I thought maybe the LCD backlight was drawing too much current, and the supply was sagging. Maybe I had accidentally increased its brightness in the code. So I set it to be really dim. No help. I removed the diode. No help.

It finally occurred to me that perhaps I wasn't giving the LCD enough time to get stable power before beginning the initialization sequence. I went looking for the lcdInit() call in the code to add a small delay before it. But I couldn't find it! Some where in last night's cleanup, I had deleted the call to initialize the LCD! The cascade of emotion that washed over me was intense. Relief that I had finally tracked down the problem, anger at the hours wasted, regret for the sleepiness I'd felt all day, all stewing in the embarrassment that I hadn't gone about the troubleshooting more methodically.

I put the call back in, and everything worked great. Phew.

But why did it sometimes work and sometimes not?

It turns out, the LCD currently doesn't get shut down when the system goes to sleep or resets. So, when I ran older code, the LCD got initialized. When I loaded newer code, it remained initialized, and so would work. But when I disconnected power in order to insert the ammeter into the circuit, the LCD reset itself. Because I was pulling power to the circuit deliberately to try to track down the problem, it was resetting itself.

So many time-consuming wrong turns, so many red herrings. In the end, it was a software problem, one I should have caught much earlier, but because I didn't carefully examine all the changes made between revisions, I didn't notice it.

Hopefully a lesson re-learned.

Not many people know that once upon a time, NASA built a Space Shuttle Launch Complex at Vandenberg Air Force Base in California, 1985. It was later dismantled, and no Shuttle was ever launched. Oh, how I wish they had kept it! I would've seen so many more launches, not having to travel across the country for each one.

Spaceflight Now has posted a series of articles with lots of photos from the era. Really great stuff.

Looks fake, doesn't it? It's not. It was built.

Each of these articles has a whole slew of images:

• Inside shuttle hangar
• Road trip to pad
• Arrival at SLC-6
• Shuttle stacked on pad
• Nighttime views
• Inside launch control room
• Final look at West Coast shuttle

In an effort to avoid cleaning for a bit, and because a friend inquired about this blog, I decided to write this short post.

In the last post, I hadn't yet received the barometric pressure sensor. It has since been installed and I wrote some code to talk to it. Unfortunately, while I'm pretty sure the SPI communications are correct, I'm getting bad data out of it. Pressures and temperatures after calibration are no good. Without the data sheet, these will be meaningless, but here's an example of what I'm seeing:

I sent an inquiry to Measurement Specialties, and they responded that they agreed the values didn't look right, but they didn't reply to my follow-up, and I got distracted with other things.

Well, that's enough procrastinating. Back to cleaning house!