Voltage Division with coarse and fine adjust

In designing the Voltage source of the last post, I originally wanted to have 2 adjustment knobs, one coarse and one fine. I concidered designs using two linear potentiometers but the fine adjustment wasn't as I wanted it to be. I wanted it to always provide a uniform range +- around the coarse setting ( I call this +- range delta V). It didn't provide this, instead it would give a large delta V when the coarse was set at one extreme and zero delta V at the other. Circuits A and B below demonstrate this effect.
I then discovered that by using a standard linear pot for the coarse adjustment and a dual gang linear pot for the fine adjustment my desire could be accomplished as represented in Circuit C.

Equations for Vout/Vin for the three circuits and corresponding plots with R1=5k, R2=100k, R3=20k are shown below. I've introduced variables x and y to represent the fraction of R2 and R3 which are enabled by the pot knob and can take values from 0 to 1. The plots show the extremes of the fine pot (y=0, y=1) for all values of x. The size of delta V can be set primarily with the value of R3. I do like this design but didn't end up using it because I was impatient and didn't have immediate acces to 5k dual gang pot. Maybe next time!

Variable DC Voltage Source

I wanted to have a DC voltage source for home projects and I decided to make one. I cheated and used a "wall wart" transformer which I picked up at the Goodwill. This takes care of AC step down transformer and rectification, I ended up adding a number of components though to protect from voltage spikes, smooth out the voltage, reduce noise and buffer the output so the load impedance has minimal effect on the voltage setting. The 100k pot sets the voltage output but there is a switch which can select between a 0 to 20V output range and a 0 to 10V output range which gives a little more control in the lower voltages.

I breadboarded most of the circuit before soldering to perf board, it seems to be working well so far but I am waiting for the analog panel meter (one of those old ones with a needle indicator) and I still need to find a nice little box to enclose it in.

This is a low current supply, I may build another one very similar but with a heavy duty 25V transformer that I have sitting around. We'll see how this Goodwill special holds up. 

Preliminary Experiments With BJTs

I've just begun to experiment with bipolar transistor amplifier configurations powered by a 9V battery and this circuit gave an interesting clipped sound. I also made one that gave a clean boost but that's not as interesting to listen to. The output of the circuit was fed into a Roland keyboard amplifier. Interestingly (and a little sadly) when I got out the guitar to test this it was the first time I had touched it in months. The next circuit I tried had high current through one branch and it fried a pnp device in about ten seconds! I'll have to put my experiments aside for a while because of a heavy school load, lots of boring school assignments to finish this week.

Setting Up Shop

These are my new lab partners: Sophie, Shazer, Shule and Sally.
They are helping me set up an electronics lab at the house. My only piece of test equipment is a handheld digital multimeter but I've started designing a simple DC Voltage source which I've been collecting some components for. After building that I will make a preamp for a ribbon mic I have.

I just got way too busy to keep up with the circuit of the day postings, in place of that I'll start updating how my projects are going. School has been busy, I've found out that layout can be very time consuming but also I've been distracted by planning my own side projects, which I'm getting very interested in. Here's to playing safely with electricity!

Day 9: ESD Protection Diodes

I took the weekend off but we're back today. My schedule may prevent me from posting daily but I'll keep putting things up when I have time. Today I look at something that I've seen quite a bit as an intern in the protection division at ON Semi.

Day 8: Ideal Op-Amp with Negative Feedback

For stability and to avoid riding the rails (clipping at the op-amp +-Vcc), the feedback path impedance must not be allowed to become too large.

Day 7: PMOS Current Mirror

Day 6: Wheatstone Bridge

This question was asked in a written test in a job interview last week.

Day 5: Diode Bridge Rectifier

I love how simple yet so genius this configuration is. So many things we plug into the wall have this in it; there must be zillions of these out there.

Day 4: Damping, 2nd Order Systems

Continuation of yesterday's circuit.

Day 3: Series RLC filter, Band Pass

Day 2: RC LPF #2

Adding a shunt resistor parallel with the cap in the RC LPF reduces gain but increases bandwidth.

Day 1: A Circuit a Day. RC LPF #1

I don't expect to keep this up long. Way too busy for that, but I've been trying to refresh my knowledge from old courses due to recent job interviews and the upcoming FE exam. Sorry to be so esoteric for all you non-circuit types (most people). It has been nice this semester to get back into circuits; I don't see myself extensively studying semiconductor physics any further. I've been wrong before though!

Musical Note Frequencies

I was thinking about how doubling the frequency of a note gives you a note one octave higher. Case in point: A 220Hz--> A440Hz, contrast this with the next octave A 440Hz --> A 880Hz and we see that the span (in Hz) of each successive octave is greater than the previous. The frequency of ascending notes has an exponential relationship that goes like 2^x. I was specifically thinking about this because the only musical note and corresponding frequency I knew was A440Hz and I wanted to know the frequency of any note I could think of. Knowing this single reference frequency and the fact stated in the first sentence of this post I found a formula that will tell the frequency of any note, I figured I would reference the formula to the 88 keys of the piano for convenience where n=1 is the lowest note and n=88 is the highest.

This graph of the above formula shows the exponential curve nicely and I've added the piano keyboard as the x-axis which corresponds to the domain of the function, integers 1 through 88. I have no immediate use for this information but I just feel better knowing that I now have an easy way to know the frequency of all the notes in western music. The formula actually works for n values less than 1 and above 88 but those probably won't get used too much.

One last thing I wanted to incorporate before I could rest was the phenomenon familiar to piano tuners called "stretch". It so happens that there is inharmonicity in pianos, especially in smaller scale and poorer made pianos but even to some extent in the finest pianos ever made. One result of this inharmonicity is that harmonics (overtones) will occur not perfectly at integer multiples of the fundamental frequency. This causes some notes to sound bad in the extreme ranges of the piano when the string is theoretically in tune to the frequencies in my little formula above. Stretching the notes sharp in the treble and flat in the bass is typically done to compensate. Additionally, I think we like to hear the high notes a little on top of the pitch anyway just to avoid the appearance of being flat. The amount of stretch depends on the piano and the mood of the piano tuner during the tuning. I have modified the formula to accommodate stretch. The .1 value can be increased or decreased for more or less stretch. All in all I think it's a decent model.

Many Changesfor Summer 2010

We have moved, it's about a 5 mile drive south west of our old location. The new house offers more space, a garage, a backyard area, a friendly neighborhood with schools and a great park nearby. We are glad to be leaving the old apartment, I've lived there longer than anywhere else second to the Rosewood house. I think everyone in the family is taking to the new house quite well.

I also started working as an intern at ON Semiconductor in the protection group which handles parts designed to protect devices mostly from electro static discharge; you don't want to kill your cell phone or laptop because you rubbed your feet on the carpet a little too much. Within the protection group I will be working with Zener diodes and TVS arrays. I am very happy about this opportunity and I believe it should set me up to be more employable come next summer when I will have graduated. This summer internship could extend into the fall semester, we will have to wait and see.

Now the bad news, we had a transmission failure in our van! I guess the '98-'01 model Odyssey doesn't have the best transmission. It will be out of the shop Wednesday and will be paid for with the help from some insurance money from our burglary incident which happened 4 weeks ago for those who hadn't heard.

All in all, things are going along pretty well I suppose. I'm sure pictures of summer activities with the kids will follow.

Digital Frequency, Sampling a Sinusoid

I am preparing for an exam in DSP (EEE 404 at ASU) and I've been confused about digital frequency. It seems like a simple enough concept but I've been getting it mixed up. So as I sort it out I decided to blog it for my benefit and because I can't seem to find many examples. If I can post a decent blog about it then I figure I'm at a point where I understand it so here it goes.
Initially I learned to use a lowercase omega for angular frequency and a lowercase f for frequency (Hz). Then in this class they use capital omega for analog angular frequency, capital F for analog frequency, lowercase omega for digital angular frequency and lowercase f for digital frequency. This little symbol change has tripped me up. I wrote out the basics to help me keep it all straight:Note that n in the above example is restricted to integer values. Now that I have all that down it should be the easiest part of the test, but let's think about the meaning of digital frequency: I believe it can be thought of as the fraction of the continuous signal's cycle that is represented by a single sample. I say fraction because if you follow Nyquist's Sampling Theorem for signal recovery (simpler explanation of Nyquist theorem here), your sampling frequency should be at least twice the frequency of the signal frequency and noting that digital frequency is the ratio of frequency to sampling frequency it is evident that digital frequency will be less than 0.5. It is possible to neglect the sampling theorem and doing so shines the light upon an important difference between discrete samples of sinusoids and their continuous counterparts: For a sampled signal with f greater than 0.5 there exists a signal with f less than 0.5 which is the same!
In the next example I have sampled a continuous signal at two different frequencies, the first with f greater than 0.5 and the second with f less than 0.5. The continuous signal is with light dashed lines and the discrete samples are bold impulses, they share the same plot (the horizontal axis thus represents both t and n). Notice that the first set of discrete points suggests a sinusoid of a lower frequency (namely 1/4th of the original frequency) and therein lies the danger in having your sampling frequency too small.I think I've got a pretty good handle on this, now I need to study all the other stuff that may be on this exam.

a few items of interest

What a great deal. Century Gateway 12 really came through for me on this one. I'm not a big movie-goer, when I go I like it to be really good and not just mildly entertaining. This movie was really good.

in other news:
I have 2 songs I have been working on recording, they are in fact mostly finished. They have drum, bass, guitar and other instrumental and even backup vocal tracks done but they both lack the lead vocals. I hope I can finish them before school starts to get busy. There's not a lot riding on it I know but if I can finish these recordings off soon I think I would be able to wholly focus on school and be a good student.

People have gotten colds and coughs at our house, Shule went in a few days ago for some shots, I've been doing more dishes by hand lately because I'm dissatisfied with the work our machine has been producing. Our little girls have been growing and doing active little kid things that make it hard to keep the house in order, but we've been doing our best to keep up. I have been applying for internships and looking more seriously into post school options.

That's what's going on and I'm not really inspired to put it all into a flowing blog post with clever anecdotes, but for what it's worth, I just wanted to get it down anyway.

Towards Mid-Junior Year

The end of the semester is in sight. Unfortunately the Thanksgiving holiday is right in the middle of some major lab assignments so I have to see that I get those mostly completed this week even though they aren't due till after holiday.

A brief overview of this semester's studies:
The circuits class has consisted of op-amps, diodes, and MOSFETs. Still to come is a section on BJTs. The lecture is great but the lab has been a huge amount of work. We still have 2 more lab assignments to do and they are very involved.

This semester's signals class was not so enlightening as last semester's but still good. Topics included sampling, modulation and transmission (mostly AM), feedback systems and root locus analysis. The LabView assignments aren't particularly exciting for me but hopefully I'm learning something.

My affection for VHDL seems to oscillate between positive and negative. I have been excited about it and hated it but right now I'm feeling pretty good about it. I like working with VHDL more than with software programming languages.

Random Signal Analysis, hasn't had much to do with signals at all yet. It's an introduction to discrete and continuous random variables regarding probablility, expectation and variance.

As I go into my last 3 semesters I plan on taking 3 more circuits courses, digital signal processing along with another signals course on filter design or some such, and properties of electronic materials. Oh yeah, next semester I have to take economics too, maybe it will be enlightening.

jellybeans

I've been stumped on this problem all weekend:

A candy factory has an endless supply of red, orange, yellow, green, blue, and violet jelly beans. The factory packages the jelly beans into jars of 100 jelly beans each. One possible color distribution, for example, is a jar of 58 red, 22 yellow, and 20 green jelly beans. As a marketing gimmick, the factory guarantees that no two jars have the same color distribution. What is the maximum number of jars the factory can produce? (Hint: Think of lining up the jelly beans, by first placing the red ones, then the orange ones, etc. You also place 5 dividers to indicate where one color ends and another starts. Note that two dividers can be adjacent if there are no jelly beans of some color.)

What do you think?

The Story of a Trombone (the wonders of steel wool)

Twelve years ago my sister-in-law Brenda, knowing that I was very interested in musical instruments of all sorts, gave me a trombone that she had played in high school. This trombone was in a fire and had suffered major cosmetic damage in addition to the case being destroyed and the mouthpiece lost; the thing was ugly.






















In an attempt to make it more presentable, I put it in the bathtub and tried to scrub the scum off; soap and water did nothing. After giving up on making it look better, I turned my focus to how it sounds. I got a mouthpiece for it and I even lucked out by getting a free case. The case, while a little bit used and shabby, looked like a dream compared to what it protected. After just a little bit of maintenance the instrument worked just fine and I proceeded to learn how to play it for a few months as a curiosity.

After a little while, it got tucked away in a corner and there it waited for many years until this year because Shule has decided to join the middle school band. Over the summer, Shule and his band director decided that he would start on the trombone. Marisa overruled my idea to send him off to school with something that looked like it was just pulled out of a landfill. She's totally right too, I fell in line quickly because in those awkward times of middle school, it may be best to not create extra opportunities for ridicule.

There was talk of renting or buying an instrument but I was developing an idea to avoid that if possible. When I came home with steel wool and a smile on my face Marisa gave me a look as if to say: "I'll humor you for a little while, but if this doesn't work we're going back to the original plan".

The finish on that trombone was cooked and in many places it was charred not just on the surface but deep into it. I worked on it for 3 days and my hands ended up sore and discolored but it worked. While I was at it I smoothed out some of the dings.


This shot was taken halfway through the process for comparison. Notice how good the bell looks next to the unfinished slide.

I can't say it looks new, but it looks like an instrument that's been used and cared for. This definitely beats buying or renting one, most rentals probably don't look this good. Since I've invested some toil, I've developed a new attachment to it and Shule is even happy to announce: "my trombone has survived a fire!".