The Fiero Project

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Some years ago my grandfather gave me an old Pontiac Fiero that had been sitting dormant for nearly twenty years. No precautions were taken to store or preserve it; it just sat outside in the elements with an undiagnosed engine problem keeping it from being moved. Once it was towed to my parents place, it sat in a garage for some years as I wondered where to begin with such a project. There where many obvious problems, and a lot needing fixing, from weathered and faded paint,and a broken windshield, to ancient gasoline in the tank, and the unknown engine problem. As I neared the end of earning a bachelors degree in Mechanical Engineering, I began to take the project much more seriously. Last summer I jumped right in and started by cleaning out the fuel system.

Starting with the basics, I turned over the engine by hand to make sure nothing was seized up. Next, I changed the fuel filter, as well as the oil and battery, which predictably did almost nothing; the engine turned over just fine but wouldn’t start. So, I jacked the whole car up and dropped the gas tank; which, by the way, was atrocious on the inside. After disposing of what was surely no longer gasoline, I hosed it out with a gallon of industrial degreaser . Followed by a good soaking with muriatic acid. I also tried using phosphoric acid, since the tank flash rusted shortly after the first cleaning. In my opinion it’s not really worth the fuss, the tank still flash rusted, and I don’t really like playing with strong chemicals. Now that it was clean I painted it and replaced the fuel pump ,and assorted rubber parts that had turned to goo.

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Before and after pictures of the inside of the gas tank.

 

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Before and after pictures of the fuel sender.

 

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The finished fuel tank and fuel sender.

 

Now surely, I though, I should get something out of the engine; and I did. What I got was what sounded like an extremely rough idle before eventually stalling. Now I was getting somewhere. Following the advice of a friend I picked up a cheap compression tester, and tested the cylinders one by one. The fourth cylinder I tested had no compression. Next step: Engine Surgery. I popped off the valve cover, and voila! A jammed valve and a snapped pushrod. From what I can gather it seems an excess amount of carbon propped the valve in an open position. Then, with no force acting on the rocker arm to keep the pushrod seated it moved out of place, the rod jammed against it, buckled, and snapped in two.

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What I found under the valve cover (left), and the broken pushrod (right).

At this point I was pretty enthused, I finally had an excuse to rebuild a sizable part of an engine.  So I pulled off the cylinder head, and tore it down until it was bare. Then I packed it all up and cleaned everything in a chemical wash basin after hours at work. I honed all the valves, and replaced the one that had jammed. I took some time while everything was apart to paint the pushrod and valve covers fire-engine red with some spray on engine enamel.

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By the time I got the head reattached, my dodge blew and intake manifold gasket, and since nothing can ever be easy on a Chrysler product, I spent the rest of what was left that summer dealing with repairs on my truck. Ultimately, I ended up getting it running well enough to trade in toward my Forester with 40,000 more miles and ten times the reliability. And so now I eagerly await this coming summer when I can finish reassembling the engine and test out the Fiero.

Why I killed my Facebook and moved to Twitter

Facebook comes with baggage and is fraught with expectation. The whole air surrounding Facebook is one charged with emotion, as the complexities of interaction and identity are watered down to a few drop down selections. In my experience, the complexity of communication as well as the need for clarification goes up. This can be observed in the application of terminologies like “like” and “friend”, the perceived simplicity of black and white selected states just leads to more ambiguity. In the analog world saying “you like something” has only one meaning, when on Facebook the convention applied to the “like” button has a much broader meaning.

“Friending” is it’s own bag of marbles. Not “Friending” or “Unfriending” a friend on Facebook can defiantly send mixed message. An “Unfriended” friend may be insulted, offended, or even hurt, perceiving a correlation with friendship in the offline world. While it could be a sign your friendship is waning, it could just as easily mean you just don’t want your feed clogged with: information you easily can or do get offline, or automated post made by apps, or any of the other dozens of reasons that have nothing to do with honest to goodness friendship. Online actions could lead to the need for offline clarifications. Time spent clarifying or repairing hurt friendships is time that could have been spent, just hanging out, having fun, or just growing closer. And, well, “friending” or “not friending” family adds it’s own dimension of fresh hell to all this.

I Dont Always - I don't always use social media But when i do i use twitter

I don’t really have too much of a gripe with any of this; after all, every form of communication has it’s strengths and weaknesses. But, the complexity and the type of friction added by using Facebook is a huge turn off for me. I turned to twitter because it’s largely neutral, following someone’s feed carries far different connotations than “Friending”. My only thought when I choose to follow someone is “Do I find their feed interesting?”, not “How will they feel if I follow or don’t follow them?”. Similarly, since twitter is public by nature, the only though I have when posting is “Is it ok if what I’m about to post goes public?”, not “Did I correctly set my up privacy settings, groups, and whatnot?” With Twitter, my focus and attention is freed up to think about what I’m posting, rather than the baggage that comes along with using the social network.

And for anything I need more than 140 characters to express, I have Cheesed-Off.

 

Field Day 2013

This Summer, I had quite a bit of fun at Field Day 2013. I joined the Saginaw Valley Amateur Radio Association for their Field Day outing. Running a Kenwood TS-520S I recently picked up, along with the matching AT-230 tuner, I strung up a G5RV antenna in some nearby trees (with help form the club). It was the first time since I got on the air with the rig since I bought it.

Field Day 2013

From 1800UTC to 0200UTC I made a total of 12 contacts, ranging in from New England to Texas, and everywhere in between. It was a great time and really got my feet wet in the world of HF.

Time (UTC) Station Frequency (MHz) Mode Location
19:11 W4RAT 14.300 USB Virginia
19:35 N0FUK 14.275 USB Iowa
19:37 W1CUM 14.320 USB New Hampshire
21:04 K4OO 14.290 USB North Carolina
23:30 K4PMH 14.290 USB Virginia
23:35 WB4ZPI 14.343 USB Alabama
23:38 WE1CT 14.275 USB ——
23:44 W5WB 14.320 USB Texas
23:50 W5CCW 14.330 USB ——
00:39 AC8IE 14.309 USB Ohio
00:58 WC9AR 14.231 USB Indiana
01:23 N5TT 14.300 USB Texas

A 2-Stage Headphone Amp Using the TPA6120 and OPA134

I recently had to design a 2 active stage amplifier for a class. So, I turned to my favorite OpAmp, the TPA6120 (check out my older post for more info about this IC). The datasheet for this IC recommends using it in conjunction with the Burr Brown OPA134, another fantastic little OpAmp. Though not quite as fast as the mighty TPA6120, the OPA134 has a very respectable 8 MHz bandwidth and 0.00008% THD.

BTW: Given the difficult to mount SO-20 PowerPad package TI uses for the TPA6120, I now offer a breakout board at AstrusLabs.com.

 For this project, I took what I had leaned from my implementation of the C-Moy amplifier design, and designed a new circuit with the same four stages as before:

Figure 1: Left Channel Amplifier Circuit

Figure 1: Left Channel Amplifier Circuit

(A) Input Stage


A potentiometer (or pot for short), R1, is used as a voltage divider to control the volume on the input side. The pot is chosen based on resistance and number of turns. The resistance of the pot should be significantly higher than the output impedance of the source (i.e. the MP3 player plugged into the amp).  The number of turns determines the resolution, a 10 turn 1kΩ will allow for more sensitive fine tuning than a single turn 1kΩ pot. I used a pair of 50kΩ single turn pots this time which seem to work well (I usually just try whatever I have on hand for this part and see what works).

(B) Filter Stage


The filter stage serves to protect the amp and headphones from a DC biased input, and prevents high frequency noise from making it’s way into the circuit. Unlike the stock CMoy design’s passive low-pass filter, this circuit uses the OPA134 (IC1) in an inverting active band-pass filter configuration; calibrated to filter out signals below 10 Hz, as well as signals above 60 kHz. The range of human hearing is about 20 Hz to 20 kHz, so this easily encompasses that with some extra padding.

To define the two cutoff frequencies (fc), the below equation is used twice:

rc_filter

Once using R2.1 and C1, for the low frequency cutoff, and once using R2.2 and C2 for the high frequency cutoff. I chose to use 1kΩ resistors for both and derived the capacitor values from there. It is notable to mention that using two different resistors will result in an application other than unity gain at this stage, so it’s best to choose the resistors first.

(C) Amplifier Stage


The amplifier stage is simply an inverting OpAmp configuration using the TPA6120 (IC2). Owing to the TPA6120’s relatively low input impedance,   developing an unwanted DC bias across the input pins has been known to be a common issue when implementing this IC. To address this, normally one would attempt to balance the path to ground resistance from each input. In this case a third resistor, R3.3, can be used to balance the path-to-ground resistance on the input pins. Because the OPA134 is in the path, calculation of this value is more difficult. To determine the correct value for R3.3, I installed a 50kΩ potentiometer, and adjusted it while monitoring the circuit with an oscilloscope. I should mention that simply grounding the non-inverting pin only results in 60mV offset, so the consequences aren’t quite as drastic as in the previous amplifier.

It may be tempting to address the issue of DC-bias with a decoupling capacitor on the front end; however, the TPA6120 datasheet specifically recommends against this solution, since it may produce undesired oscillations on the output signal. The datasheet also offers a lot of other good design considerations, and I do recommend reading it over before modifying or designing your own amplifier.

 (D) The Driven Load


This portion of the circuit represents the impedance of the speakers being driven. In my case this would be the impedance of one side of a pair of AKG K-240 Studio headphones, or 55Ω.

 Other Considerations


The TPA6120 is a very finicky IC, and requires very clean power. It is necessary to use decoupling capacitors (preferably low ESR, though I’ve had good results with electrolytics too) .

 

Creative Commons License A 2-Stage Headphone Amp Using the TPA6120 and OPA134 Blog Post by Cheesed-Off.com is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

Some Good HAM Exam Prep Resources

If you’re like me, you like to run through practice questions to prepare for tests. Here is a short list of resources I’ve used, and recommend.

 

Web: http://hamexam.org/

A simple site that just runs you through test questions. Definitely a great free resource.

 

Android: Amateur Radio Exams 1.0 Pro

Aside from the $2 price tag, and slightly humorous contradiction in the name, this is a pretty rock solid little app. It has numerous useful test modes, including: random, previously unanswered, previously incorrect, and all questions test modes. It also remembers where you last left off and offers an option to resume from that point. The real selling point of this app, though it’s not terribly unique, is that you can study anywhere without fumbling through your phone’s browser.

 

iPhone: Unknown

I don’t own an iPhone, but I’ll be happy to take app recommendations and post them here. Feel free to email me at deseehc@kcabdeef-off.com if you know of a particularly useful app.