Print Story The Tale Of The Exploding Car
By DesiredUsername (Thu Aug 24, 2006 at 04:07:09 AM EST) (all tags)
And other stories.

So I'm driving home, right? I'm maybe a mile over the boarder from MA to NH and I hear this tiny fluttering sound coming from the engine. Is that mine or the car next to me? Speed up, slow down--yeah, that's me. Then the fluttering gets a little louder. Then it suddenly turns into a rattle and gets really loud (this is less than a minute from onset). Then BANG! something flies out the bottom of the engine and I see a rod bouncing out behind the car. I'm in the far left lane so I have to pull into the median with a suddenly dead car. As I stop, vast clouds of smoke start pouring out from under the hood.

So there I am, trapped between 70+ mph traffic and more 70+ mph traffic in a cloud of smoke. I guess someone called 911 because not only did the police show up, but two firetrucks. Fortunately the smoke was "just" just the oil that didn't drain out onto the ground burning up.

Long story short: They say it would cost $5000 (or $4200 because I'm such a nice guy) to get a new-to-me engine (plus some other work), but since this is a 10 year old car and I have another I can drive I'm thinking I'll pass. The dealer service manager wants to personally buy the car, though--the body is in perfect shape and I suppose he can get a better deal or even fix it himself.

I'll probably buy a Yaris (or, less likely, a Prius) in April when we aren't sending $N/month to Number Two's kindergarten. Just because I can drive the truck to work doesn't mean I want to spend $M/week on gas.

I'm sure The Art Of Electronics (and the Student Manual for same) is truly awesome for someone who already knows the subject and thinks they can judge it objectively, but it's ability to teach to the n00b is severely overrated. I really want to like the book since it's written so well, but it jumps in so fast and with so little explanation it's just impossible learn from.

Oscilloscope prices are crazy. New is totally out of the question ($2000 is a basic starting price). Even used is pretty crazy, with $300 being a typical junker price. So I got an old computer from freecycle (which happened to come with a pristine 17" monitor, omgwtf!) and installed Winscope. It only works in audio frequencies, but that's better than both a) nothing and b) $300.

I put a microphone on it and the Numbers and I had a good time shouting at it to make it wiggle. One lost interest pretty fast, but Two made several discoveries, such as how to make the FFT display move left and right by singing up and down the scale. Later I attached a miniplug to alligator clips and tried to drive it with a function generator. That worked...kind of. I think it will work better once I know wtf I'm doing. Like, what does "trigger" mean?

You may remember the train track AND gate:

The problem with this design is that the state of the switches encodes the bit values and reading those switches with other trains is problematic. The solution, as my officemate and I both realized, is to encode the bit values in the location of the train instead. That is, an AND switch would have 4 inputs (0 or 1 for the first bit and 0 or 1 for the second) and 2 outputs (0 or 1).

After a little messing around and a tiny bit of cheating we were able to design an AND gate that worked this way. I put it together this weekend, using exactly as many switches as our set has, and it worked. I even took pictures but I haven't posted them yet because IAAD.

I'm thinking a smaller-than-N scale train set, especially if it could represent logic gates, would be a great ThinkGeek-type desk toy.

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The Tale Of The Exploding Car | 15 comments (15 topical, 0 hidden) | Trackback
Engine replacements bite by georgeha (2.00 / 0) #1 Thu Aug 24, 2006 at 04:35:13 AM EST
I reckon our Volvo replacement ran about 6-7k, six years ago.

Why does it cost money for kindergarten, are there no public ones?

PUBLIC KINDERGARTEN?? by DesiredUsername (2.00 / 0) #4 Thu Aug 24, 2006 at 04:47:09 AM EST
What are you, a COMMIE?!?!?!?!

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[ Parent ]
We're talking aboot NH by ad hoc (2.00 / 0) #10 Thu Aug 24, 2006 at 07:06:57 AM EST
They charge for school busses, too.

Live free or die, baby.
Close friendships and a private room can offer most of the things love does.

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No they don't by DesiredUsername (2.00 / 0) #11 Thu Aug 24, 2006 at 07:19:37 AM EST
At least not separately.

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They do in Nashua by ad hoc (2.00 / 0) #12 Thu Aug 24, 2006 at 08:08:41 AM EST
Trigger by garlic (2.00 / 0) #2 Thu Aug 24, 2006 at 04:37:37 AM EST
means capture data only when the signal amplitude crosses this programmable value. It can sometimes be set for rising or falling edges. I use triggers in digital logic and with multiple inputs so I can see the relationship of multiple signals based off an event on one signal.

OK, so for a sine wave, say by DesiredUsername (2.00 / 0) #5 Thu Aug 24, 2006 at 04:48:26 AM EST
If you set the trigger to 0, does that mean the trace will start at 0 at the left and not appear to change phase? Because it wasn't doing that (probably because I was doing it wrong).

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maybe by garlic (2.00 / 0) #6 Thu Aug 24, 2006 at 05:20:31 AM EST
3 points are important here: What amplitude do you set the trigger to, what location in the display do you have the trigger lined up with, and whether it'll trigger on rising, falling, or any transition.

[ Parent ]
Well, I'll have to mess with it by DesiredUsername (2.00 / 0) #7 Thu Aug 24, 2006 at 05:41:45 AM EST
Using myself saying "eeeeeee" probably isn't the best signal source.

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EEEEEE is fine by darkcity (2.00 / 0) #8 Thu Aug 24, 2006 at 06:43:19 AM EST
Since you're using a computer based scope, it will probably work like this:

The scope is constantly sampling at some frequency and stuffing those samples into a buffer.  When the trigger event occurs, the scope continues sampling for a fixed length of time and then displays the contents of the buffer.

You can probably adjust the timing of the trigger point - 10%, 50% and 90% are typical presets.  That means it will display 10, 50 or 90% of the data accumulated before the triggering event occured.  Looking at the Winscope page, this would appear to correspond to the "Delay" setting.  For a periodic signal, this setting doesn't really matter.

As garlic said, you can set the trigger to rising, falling or any transition.  For your case, any transition would be fine.  All you have to do is set the voltage level correctly.

An easy way to do this is to speak into the microphone and adjust the trigger voltage level until the scope is triggering the way you want it to.  This is the "Trigger Level".  So if you set it to 0, it means that the scope will not display anything until the signal crosses 0V.  The Winscope page isn't very clear as to the units of the trigger level (V? mV?)

I managed to pick up an ancient analog scope at a garage sale last month for $5 - it even works.  It was a perfect buy to set up a similar microphone "playtoy" for my 2 year old.

[ Parent ]
Actually, I have an ancient Heathkit scope by DesiredUsername (2.00 / 0) #9 Thu Aug 24, 2006 at 06:55:58 AM EST
but only the vertical works. Or maybe I'm not using it right.

Thanks for the tips, I'll try this.

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I bet the marketroids had fun with namingthat Ford by Breaker (2.00 / 0) #3 Thu Aug 24, 2006 at 04:42:28 AM EST

Uh huh.  Uh huhuh.
Pass the coke, Jezza.
Uh huh.  Uh huhuh.

That reminds me by skippy (2.00 / 0) #13 Thu Aug 24, 2006 at 11:06:58 AM EST
I've been meaning to get an oscilloscope for a while.  What I'll probably end up doing will be getting a cheap National Instruments 12-bit USB DAQ (maybe 16-bit if I splurge) and then just observing the output in Labview.

Now, if only I can convince the wife that I somehow need that DAQ for the renovations at home...

Duh. by skippy (2.00 / 0) #14 Thu Aug 24, 2006 at 11:08:28 AM EST
Reading at the Winscope page, that reminds me even further that I don't need to bother with the USB DAQ, I can just use Labview's sound card input function to do the same thing, since I'll be working with audio frequency (and level) signals anyways.  Woo!

[ Parent ]
Computer scopes by wiredog (2.00 / 0) #15 Thu Aug 24, 2006 at 05:46:44 PM EST
Look around for a decent a/d card. Those can make pretty decent scopes, depending on what you're scoping.

Bck when I did automated process equipment programming I lusted after a Fluke Scopemeter. O-scope+VOM in one package that you could hold in your hand, and you could hook it up to a PC to gather lots of data. But thay cost $2000 10 years ago.

Earth First!
(We can strip mine the rest later.)

The Tale Of The Exploding Car | 15 comments (15 topical, 0 hidden) | Trackback