Learning electronics: Release the Magic Blue Smoke

The Something Awful Forums > Discussion > Hobbies, Crafts, & Houses > Learning electronics: Release the Magic Blue Smoke

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Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

Metajo Cum Dumpster posted:

Don't forget, Jan 7 9am-11pm mst Sparkfun is giving everyone $100 credit towards anything on the store.

What does this mean exactly? It sounds neat though.

# ¿ Jan 2, 2010 21:04

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# ¿ May 22, 2024 00:19

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

macpod posted:

The simplified analogy I am thinking of involves water in a trough. If the trough has a consistent width, then no "feedback" waves will be generated. On other hand, if the trough suddenly has a "step" that is narrower than the previous step, some water will hit the barrier and generate a wave that is bounced back to the source. Is that an ok way to think of it?

Yes, this is a good way to think of it.

macpod posted:

Out of curiosity now, lets say you have a funnel-like transmission line where the source end is narrow and the destination side is wide. What would the effects be?

This would be a matching circuit!

macpod posted:

The trace I made goes between the reciever chip and an active antenna. Since it is a transmission line vs a microstrip antenna, I should be more concerned with keeping the line short vs. matching to wavelengths, right? Or do I need to go by some golden ratio?
From the little bit of reading I am doing now regarding transmission lines, it seems I shouldn't have much of a problem as long as the length is under 1/4th a wavelength (a little under 2" for gps). I beleive they call these "electrically short" transmission lines.

So long as the chip input is 50-ohms and your antenna output is 50-ohms (is it really?) then the length of your trace, assuming its 50-ohms, doesn't matter (okay, not quite true, since you'll introduct resistive losses). But yes, try to keep it short.

# ¿ Jan 4, 2010 04:02

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

ANIME AKBAR posted:

I've never worked with active antennas before, but I would imagine that in this case the trace going from the active antenna to the gps chip isn't very critical at all. All the critical stuff should be built into the antenna chip. That's generally the point of fancy components like that...

Whatever calculation he used for the strip will probably put it at something like 40 - 60 ohms, which is definitely good enough.

macpod posted:

The antenna says it needs a 50 ohm trace, as does the receiver so I assume so. This is the data sheet:
http://www.sarantel.com/downloads/specifications/SL1206_SL1204%20Electrical_Guide_v10.pdf
They suggest to keep it close to the IC to minimize loss.. in my case I guess the advantage would be reducing resistance since it's already an electrically short trace.

So right now I'll try and shorten the trace by rotating the receiver chip 45 degrees and running the trace all the way to the rfin pin. I'm going to put in a 0.1uF and 1uF cap on the IC's vin line to gnd line as close to the chip as suggested too. Should I try to filter the rx/tx lines going to the chip too or will this matter? Any other comments to filter power better other than adding a regulator?

No, filters on your tx/rx lines are not necessary.

Why 0.1uF and 1uF? You might want to consider adding series chokes (several uH SMT chokes exist) to your power lines as well.

Cyril Sneer fucked around with this message at 06:31 on Jan 5, 2010

# ¿ Jan 5, 2010 06:28

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

ANIME AKBAR posted:

photodiodes are generally quite directional, so that's going to be a big problem. try to find emitters and detectors with very large viewing angles/half power angles, and don't operate near those constraints. transconductance matching is an issue to, but that can be calibrated away if necessary.

the only time you want ferrite beads is when you want to kill noise from digital circuits from propagating into sensitive analog circuits that share a supply rail. If your chip has separate supply pins for digital and analog, then it might be worthwhile. however, if not, then they will almost certainly increase noise instead of killing it. I would consult the documentation on the chip and look for appnotes on supply filtering. If it doesn't explicitly mention it, then it's probably not necessary.

Where did ferrite beads come from? By chokes I'm referring to inductors, which I thought was standard usage.

# ¿ Jan 6, 2010 01:14

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

How would I go about actually programming/compiling to my arduino in C? I know they provide their Sketchbook development environment, but I want to strip away as many layers (short of assembly, at least) as possible. Also, I'd like to be able to compile executables, which I can't do within the Sketchbook environment.

Cyril Sneer fucked around with this message at 06:00 on Jan 9, 2010

# ¿ Jan 9, 2010 05:57

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

BattleMaster posted:

Also, my limited understanding of radio is that if you use a unipole antenna, you need to design the ground plane of the PCB to match it to act as the second pole. I want to avoid that because I have only the tools and skill to make single-sided PCBs so I was thinking of using bipole antennae instead. Would that work?

This is technically true, but often not followed in practice. All sorts of electrical devices use electrically short whip/monopole antennas, with the ground plane being somewhat of a "don't care". Electrically short antennas just won't be all that efficient; though they will still radiate of course.

# ¿ Jan 14, 2010 04:45

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

Vivek posted:

Can anyone explain to me what a bias tee is? According to Wikipedia it seems to separate high and low frequencies, but I'm not sure what that has to do with biasing.

A bias-tee separates or mixes DC and RF signals. A typical bias-tee circuit consists of a capacitor between the input and output and a choke on one side to ground. The RF passes through the cap unimpeded while the DC is shorted to ground.

# ¿ Feb 11, 2010 04:33

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

A crystal is a two-pin device and is just the piece of crystal itself. This alone does not product a signal - it needs to be part of some sort of feedback circuit in order sustain oscillations.

A resonator or oscillator, when referring to an IC, generally means a 4-pin device that includes a crystal and appropriate circuitry all built in - you supply Vin and GND, and it gives you your oscillating signal.

# ¿ Mar 8, 2010 04:25

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

CptAJ posted:

Hey dudes!

I'm in need of some of your fine guidance here. I've been looking into building a homemade wifi antenna. Looking around the web I can see there's tons of these little crazy gadgets.

I'm gonna go for a yagi antenna, following this guide here. It seems simple enough to build but I've got a few questions:

1- Would it be better to build the beam out of copper or some other metal instead of wood?
2- Is there gonna be a problem if I use a coaxial cable of about... I dont know, lets say 5 meters? Mounting the antenna on the roof and throwing a wire down to my computer room and into a regular PCI interface card.
3- Do you know of a better guide or antenna alternative?

Thats it for now. I might come back with some more questions later. Now I'll go read a little more about the scienc of how these antennas work.

Thanks

[edit] Ok, after a little reading, I'm thinking the coaxial thing is gonna be an issue. Right? I figured there was only one kind of coaxial cable. I only have the cable TV one. Could someone point me in the right direction here? I really need to figure out the cable issue. I don't want to go for a USB dongle setup since the USB cables are limited to less than 5m

1) No, the vertical rungs need to be insulated from each other.

2) The coax needs to be kept short. You're not picking up that much power with the antenna and it's going to see lots of loss (relatively speaking) through that 5m of coax.

3) You need to either have the dongle/amplifier physically at the antenna, or you'll have to located the antenna in close proximity to your PC.

# ¿ Mar 27, 2010 17:15

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

BattleMaster posted:

I thought it would be a neat project to build a hot cathode electron gun like the one described on this page. Has anyone built one before? Are there are any safety hazards beyond the standard wall power precautions? What are some suggestions for the design and materials?

Edit: I am mainly concerned with the tube itself building up a deadly charge. I know CRTs build up big charges but I'm not sure if that's the tube itself or the capacitors in the circuit. None of the home-made electron gun sites I've found mention it either way.

Production of x-rays I'd say would be your biggest concern.

I'm not sure either if the charge warnings come about as a result of the tube or caps used in the circuitry.

# ¿ Apr 20, 2010 04:14

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

BattleMaster posted:

I've read about X-ray emissions, but I'll be sure to look into it further. From what I've seen so far, at under several kilovolts the risk is minimal. A hot cathode setup with a voltage of only 100-200 shouldn't be that much more dangerous than a tube diode, right? I mean they work pretty much exactly the same way.

Edit: But if the danger has been greatly downplayed by others maybe I'll just forget about it entirely.

It's not the cathode that matters, its your accelerating voltage.

But yes, at 'low' power levels I wouldn't worry about it.

# ¿ Apr 20, 2010 04:49

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

I was having a discussion recently regarding the breakdown voltage of a given material at a particular thickness. Common wisdom has it that you can test a thin slice of material to find its breakdown voltage and then linearly scale this to greater thicknesses. I.e., instead of testing a 1cm-thick sample to breakdown, you could instead test a 1mm-thick sample and just multiply that result by 10.

Now, I don't believe that this is generally true. As you increase the thickness of a material you increase the number of defects that occur within its volume and ultimately reduce its overall voltage standoff capability. To put it the other way, a very thin slice can have superior voltage standoff capability, as compared to a thicker slice, as such a slice can be nearly defect-free. Capacitor manufacturers strive to use very thin, defect-free dielectrics exactly for this reason.

Basically, I'm just trying to find a website or some papers that discuss this. I'm quite certain I am correct but I need proper proof.

(I'm well aware that it is material and manfucturing dependent, and that there is an optimization curve that occurs between thickness and defects. I'm thinking that the way it all plays out is that the described effect is valid, but only for slices less than some "average defect size" parameter)

# ¿ May 12, 2010 05:46

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

ANIME AKBAR posted:

Dielectric breakdown voltage is simply a convenient extension of the dielectric strength, which specifies the E field strength at which avalanche occurs. Theoretically, multiplying dielectric strength by thickness gives you breakdown voltage.

The "theoretically" is where this falls apart: it assumes no defects in the material.

The wikipedia article on dielectric strength makes some mention of this: http://en.wikipedia.org/wiki/Dielectric_strength

ANIME AKBAR posted:

Only an increase in defect density would change the dielectric strength of a bulk material. I can't think of a reason why thicker samples would have an inherently higher concentration of defects (though some nuances in manufacturing may lead to this).
If thin layers have smaller defect concentrations, its due to different manufacturing techniques which are only feasible for thin layers. For those of us who don't sputter or chemically deposit insulation on our wires, its irrelevant, and four mils of kapton will indeed have twice the standoff voltage of two mils of kapton.

If a bulk material has, statistically, one defect per million molecules (or per crystal, or per grain - or however such things are characterized) than a sample containing only 500,000 molecules may not contain any defects. This defect-free sample will present a higher dielectric strength than a similar sample containing a million molecules and a single defect.

ANIME AKBAR posted:

your "defect size" is likely going to be in the range of tens of microns, max. do you really have an application for which this is relevant, or is this simply food for thought?

Food for thought in the name of precision and accuracy.

Take a look at the following paper: http://www.arlonstd.com/Library/Guides/Effect%20of%20Elastic%20Elongation%20on%20Dielectric%20Strength.pdf

They demonstrate that in stretching a variety of film tapes - resulting in a thinner cross-section - their dielectric strength increases.

# ¿ May 13, 2010 06:20

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

SnoPuppy posted:

That sounds like a sampling problem to me. If you know you have defects at a specific rate, why would you characterize the material in a way that makes seeing defects unlikely? At this point you're effectively changing the material - you go from bulk dielectric to "defect free" dielectric.

In general, approximations hold true for one scale, but break down when you begin to start violating their assumptions.
And that's all that dielectric strength is - someone measured some number of samples under specific conditions. You change those conditions, and the measurement (and extrapolated results) no longer hold true.

I agree with all of this. I think we're saying the same thing.

When you look up a table of dielectric strengths, those values were all measured for some specific thickness (we'll ignore environment and frequency for the time being). If you test at a different thickness I think this constitutes a change to the test setup, as I don't believe you can assume the dielectric constant to be the same; this represents an extrapolated result, as you say.

Yes, of course the relationship of breakdown voltage = thickness * dielectric constant is always true. What I'm suggesting is that you cannot assume the dielectric constant, in the practical-real-manufacturing world to be same for a thin slice and a thick slab.

# ¿ May 13, 2010 14:13

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

ANIME AKBAR posted:

So I guess that after searching for someone to do master's research for (the guy I originally intended to study with went on surprise sabbatical), it looks like I'll be doing MRI systems and electronics. Apparently I'll be trying to create the world's smallest/most inexpensive MR unit (smaller than a coffee can, less than $1K). The electronics aspects seem pretty neat, but the physics of MR is loving mindboggling to me.

From way back, but what sort of main field strength are you aiming to generate?

# ¿ Jun 12, 2010 00:48

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

ANIME AKBAR posted:

IIRC, the magnet is about 0.15 tesla (permanent magnet of course), so my Larmor frequency is around 14MHz.

Cool. Are you planning on actually acquiring images or just do spectroscopy?

# ¿ Jun 14, 2010 04:50

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

ANIME AKBAR posted:

Our giant musical solid state tesla coil has seen its first light:

unfortunately the guys in charge of making the audio signals dropped the ball so we couldn't play actual music that night, but whatever.

Put a toroid on that thing. Tesla coils somehow are just not asthetically pleasing without them.

# ¿ Jun 18, 2010 02:27

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

Not sure if anyone would know the answer to this but I'll ask anyway. I guess my next stop would be the fine folks over at pupman.com

Lets say we have a nice, single-shot DC electric discharge. This produces a broadband response in the frequency domain. What happens as we increase the discharge frequncy? From say, once per minute, to once per second, to kilohertz, to megahertz? Basically, what is the frequency content of a, say, 100 MHz electric discharge (at say 1 Hz, each pulse stands alone and produces a wideband frequency response, but what happens as that time-frequency increases and one event "blurs" into the next [a kind of intersymbol interference])?

Along a similar line, is there a difference, frequency-spectrum-wise, between a spark and an arc (an arc being a continuous sustained plasma channel)? And how does oscillation frequency factor in?

# ¿ Jul 31, 2010 21:25

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

Hillridge posted:

I was cleaning my junk room and found my 15kV 30mA transformer. What's a good place to start when learning about Tesla coil design? I may eventually want to make this a musical coil as well since I also found a lovely keyboard in the junk room.

I know I've seen a few coilers in this thread.

https://www.pupman.com

Just keep reading and reading and reading.

# ¿ Sep 8, 2010 04:05

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

Unparagoned posted:

Software questions: What's the best software to use. I like Falstad Circuit Simulator but it's slow and and very limited. From what I can gather is I want is some kind of spice but with a decent interface. I think I want spices power with a Falstad circuit simulator interface. Any advice

Why everyone isn't using MicroCap is beyond me.

Krenzo posted:

I'm going off of research papers and books that are written on the subject. They have actual products out now that work on this technology. I would probably have given up by now if there were no papers and examples for me to work from. Here's a good thesis paper I found on the subject: http://scholar.lib.vt.edu/theses/available/etd-09192006-230733/unrestricted/Anderson_Final_ETD_Version.pdf

Also, this is really neat!

Cyril Sneer fucked around with this message at 04:55 on Dec 9, 2010

# ¿ Dec 9, 2010 04:37

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

ANIME AKBAR posted:

Never heard of this before. How are its component libraries? What version are you using?

http://www.spectrum-soft.com/index.shtm

I'm using the latest version. Its component library is great; but it's its interface that really makes it shine.

# ¿ Dec 10, 2010 06:58

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

BattleMaster posted:

Hey while we're talking about square waves, how does capacitive/inductive reactance work with square waves? The formulas for both have 2*pi*f in them so I assume they're for sine waves.

It depends entirely on the circuit itself. As mentioned, a square wave is really a collection of an infinite sum of sines across frequency. Feeding a square wave into a lowpass filter (RC circuit) will attenuate the high frequncy components producing an output waveform with rounded edges. Feeding a square wave into a highpass filter will give a weird kind of sloped-pointy waveform as the low frequencies are attenuated.

# ¿ Dec 21, 2010 05:52

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

Does anyone here have much EMI/EMC experience? I'm looking at picking up either -

Ott's book:

http://www.amazon.com/Electromagnetic-Compatibility-Engineering-Henry-Ott/dp/0470189304/ref=sr_1_1?ie=UTF8&qid=1297122652&sr=8-1

or Clayton:

http://www.amazon.com/Introduction-...97122652&sr=8-2

I deal mainly in the ~100's MHz, and nothing really digital so I'm looking mainly for a good treatment on coaxial terminations, shield currents, ground loops, etc.

# ¿ Feb 8, 2011 00:53

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

ANIME AKBAR posted:

Oh and if it makes you feel any better, one of the other grad students in my group has to transmit a 64MHz NMR signal over a wireless channel at 900MHz, and it needs less than 5ppm of phase error/jitter at the end. And their are eight independent channels of that which have to be phase matched to 1ppm. And believe me, those errors matter...

He's not working on wireless receive coils is he?

Why not digitize at the source?

# ¿ Feb 9, 2011 06:44

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

ANIME AKBAR posted:

Yes.

Because then you would have to completely reengineer the scanner hardware to accept digital data. And that would be... expensive.

I'm actually jealous. I've tried to convince my superiors of the value of such a project but it keeps falling on deaf ears.

You don't have to completely reengineer the scanner. Do your ADC and Tx at the coil, then do your Rx and DAC inside a module that plugs into the doghouse.

There's at least one company out there that manufacturs such a module, and the big vendors are going to be incorporating this functionality into their future hardware.

# ¿ Feb 11, 2011 01:33

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

I'm thinking of making a giant LED matrix. I'm talking 16 x 38 RGB leds. Unfolding this out, its 16 x 114 'effective' rows and columns. I'm envisioning controlling the rows and columns by serial shifting in of the bits and activing each of the 16 rows consecutively.

Where I'm struggling is the best way to latch the bits and provide the power for the rows and columns. I could just use 16 x 114 individual power transistors, and string together enough shift registers to build my 16 x 114 grid but I have to believe there's a better way (i.e, some sort of combined shift-latch-driver chip?)

# ¿ Feb 23, 2011 03:41

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

Slanderer posted:

Seconding the suggestion of looking at Chroma for reference. TI makes a bunch of chips in that line with slightly different features, so there might be one that's better for you. I don't exactly agree with their solution of slightly multiplexing the LED controller chips, as it just adds extra complication (and the chips are cheap anyway). They also had a microcontroller on each board; One could probably ditch that, and just control all the LED controllers over the SPI bus from one micro.

This is also an interesting project design:
http://hackaday.com/2010/11/21/led-wall-and-kinect-join-forces/#more-30985

The build log isn't in english, but that's not really an issue, honestly. They go with an LED controller from Maxim, but its nothing out of the ordinary.

However, if you have/find a good supplier of RGB LEDs, please spread the word. They're drat expensive to get here, even in big quantities. Chroma's author found a supplier they liked on ebay selling for 50% of the price. That makes it much more reasonable, but shipping across the pacific is annoying, and the lifetime of unbranded, high brightness LEDs can be...questionable (ie, things like dropping to 50% intensity almost right away). This kind of project is already expensive enough to get the PCBs printed, so I'd hate to spend even more on just LEDs.

Thanks - that project is basically exactly what I'm looking to do.

There's a guy on ebay selling 600 RGB LEDs for $100, shipping included, to Canada (where I am).

# ¿ Feb 25, 2011 04:32

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

Lets see if I'm thinking through this correctly:

I have a matrix of 16 x 38 RGB LEDs, or a total of, effectively, 1824 LEDs. The TLC5947 IC can drive 24 channels, so I will require 76 of them. Just to be clear, we note that although they will be arranged in a matrix, we are not actually controlling them this way.

Each channel accepts 12-bits of PWM data, thus to fully initialize a single IC, I need to shift in 288 bits. A single panel refresh would therefore involve shifting in 288 x 76 = 21,888 bits.

Given that, how can I ascertain if I can expect reasonable refresh rates if I intend to drive it with an atmega328 arduino?

Cyril Sneer fucked around with this message at 05:38 on Feb 25, 2011

# ¿ Feb 25, 2011 05:35

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

This thread needs more controversial RF discussion!

Lets say you have a source feeding a 50-ohm coax line. The load consists of a 50-ohm resistor soldered between the centre conductor and shield. Under this scenario, all the current travelling down the centre conductor returns via the inner surface of the shield. These two currents, flowing in opposite directions, perfectly cancel and so the coax does not radiate.

Now assume the load is mismatched. Reflections occur, causing some phase shift between the forward and reverse currents. This results in a standing wave along the line. For a given infinitesimal length, the current on the centre conductor and the reverse current on the inner shield are no longer equal and opposite. Field cancellation does not occur and the line now radiates.

Or does it?

An opposing view holds that the shielding effect in coaxial cable occurs as a result of the skin effect and has nothing to do with field cancellation. Assuming we're working at reasonably high frequencies, the thickness of the shielding used in coax is several times larger than the skin depth, thus ensuring nothing "gets through" the shield.

Here's an interesting thought experiment. Imagine we have a 50-ohm source supplying a constant voltage. We have some length of coax terminated by some arbitrary load. We can reflect this load back to the source and calculate an equivalent lumped impedance and the resulting power delivered by the source. If we actually carry out this experiment, and we take the load to be mismatched, would we measure the power to match the calculation described, or would be larger, as a result of the radiation loss due to the standing wave formed by the mismatch?

tl;dr: Does a coaxial cable carrying a standing wave radiate? Yes or no, and why?

# ¿ Mar 5, 2011 05:51

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

Corla Plankun posted:

No, because standing waves' time-averaged powerflows are zero according to my electromagnetics textbook.

So this implies that coaxial shielding functions as a result of the skin effect and not field cancellation. Why then do many sources claim that it is necessary to ensure that the centure conductor current must all be returned on the shield lest we end up having normal rather than differential current flow?

# ¿ Mar 5, 2011 21:17

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

ANIME AKBAR posted:

It's what I'm currently developing for my masters degree. The goal at this point is to make a system that could be used in an educational environment, for students learning about NMR systems. It's all built with off the shelf components, and its actually powered by an arduino (my advisor's idea, not mine...). It's not terrible complicated, but it can't yet do imaging, just NMR experiments (T1, T2, diffusion measurement, etc).

There are a few companies out there offering this sort of thing already - are you involved with them at all?

IAmCorbin posted:

I am new to playing around with building my own circuits and am getting into BEAM robotics. I have been studying solar engines and just got some parts in the mail from http://www.solarbotics.com/

I just wired up this simple 1381-based solar engine circuit (http://www.solarbotics.net/library/circuits/se_t1_1381.html) circuit on a breadboard. I can't seem to get it to work though.

I have an oscilloscope that I have hooked up to the cap so I can watch it charge, but it gets up to 2.7V and just sits there, never dissipating to power the motor. If I bridge the motor to the negative side of the cap directly it runs for a moment as expected.

The fact that the cap never discharges indicates you've got an open circuit somewhere. Check your connections. Be sure you've got your pins all wired the right way around.

Try monitoring the base of the 2N3904 - this should tell you if the 1381 is activating properly.

Cyril Sneer fucked around with this message at 04:09 on Jul 13, 2011

# ¿ Jul 13, 2011 04:06

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

IAmCorbin posted:

With the 1381 circuit it just reaches the peak and never discharges

Does anyone have any suggestions on how I can further test the 1381-based engine circuit? or how to properly test a 1381?

[edit]

Have you tried using the 1381 alone, out of circuit?

I would hook up the 1381 by itself and feed it with an adjustable voltage source to see if it ever triggers at all.

# ¿ Jul 14, 2011 23:35

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

Krenzo posted:

L1 has the highest SRF (1.2 GHz) I could find and matches the eval board bill of materials. I did not know caps have SRF values. I'll have to look into that. Edit: There's no SRF value in the datasheet. It's just a generic ceramic cap.

Yes, the components are the same. Yes, I designed the traces to be 50 ohm microstrip, and the board thickness is about the same as the eval board. The dielectric constant is around 5, but the manufacturer only gives this value at 1 MHz. Reflections from impedance mismatch sounds like the most probable issue if the transistor is amplifying them. This photosensitive process isn't anywhere as precise as I was hoping it would be. The trace widths come out different sizes each time.

I guess I'll just try to put a low pass filter in the circuit.

I didn't see it mentioned but what frequency is this operating at?

Have you done a full set of s-parameter measurements to ensure you're input and output impedances are what they should be, and that your transmit and isolation values are "reasonable"?

I would guess that inductor has something to do with it. When its powered is it drawing the correct current, and is it stable? I've used all those components on similar boards and those inductors can be a bitch.

edit: also, you want to be really careful you didn't delaminate any of those caps - its not always easy to tell visually.

Cyril Sneer fucked around with this message at 02:29 on Jul 23, 2011

# ¿ Jul 23, 2011 02:21

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

taqueso posted:

I've been reading through these EMC articles by Keith Armstrong over the last couple days. There is a bunch of good info here:
http://www.compliance-club.com/Search.aspx?keyword=keith%20armstrong

You have to make an account to view these, but I haven't gotten any emails from them since signing up.

Registered. Some neat looking stuff on there. I don't know what it is about EMC that I can just spend hours and hours reading about it.

# ¿ Aug 2, 2011 21:26

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

movax posted:

My problem isn't with the Arduino so much, it's more some Arduino users running around after writing a few sketches believing they're embedded experts and dispensing horrible advice (i.e. not every problem in the world calls for an Arduino, nor can it be solved by an Arduino). Nothing's more frustrating than having a guy who used an Arduino once getting pissed at you because you're not listening to his "expert advice" about using an Arduino plus some obnoxiously priced PWM shields to control a DC/DC converter as opposed to a $6 one-chip solution with a dsPIC. And then watching like 12 other people run out and drop $75 on "maker kits" that are essentially an Arduino + LEDs + insane markup.

Though, the legit complaints I have heard second-hand is that it can be a bit difficult to "hack" in your own functionality / try to get some lower-level access in conjunction with your sketch without some library functionality. There was a guy trying to play with the timers on the AVR, but he couldn't get that to play nice with the rest of his sketch in Processing and ended up learning how to do the whole thing in C.

Personally I think a lot of Arduino shields are overpriced too, but that's probably just me.

You would be a good person to ask. I have an adruino and so far all I've done is play around with it using its own IDE (though I've written C code to communicate with it after the fact). I'd like to start coding in pure C/C++ and do the compiling and downloading myself. Do you know of any good sites that describe the process? I'm quite competent with coding, I just don't know much about what libraries and compiliers I would need to do this.

# ¿ Aug 19, 2011 02:21

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

Have any of you guys used any of those portable digital DSOs that tend to pop up on ebay quite a bit? Are they any good?

Krenzo posted:

After thinking it over, I'm going to put all of the elements that need to be unshielded (the antennas) on the backside of the board and all of the shielded components including microstrip traces on the frontside with vias connecting to the antennas. Then, I'll shield the frontside with an enclosure and with a solid ground layer beneath. I just don't know if the antennas will tolerate a ground layer underneath (destructive interference/reflections?) as that's contrary to the suggested floor plan in their datasheet, but I fully accept that the antennas will not receive a signal through the ground plane.

I'm still not following what you're trying to do. It sounds like you're trying to "shield an antenna", which would prevent it from ever working. Anything that breaks out of the shielded environment (such as your antenna feedpoint) is going to pick up some amount of RF.

# ¿ Oct 28, 2011 05:17

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

I'm going to respond to your post in reverse order, as I think that'll make mroe sense

Krenzo posted:

I made an open circuit between the antenna and the switch. It still picked up the signal with the switch set to that antenna. I then disconnected the whole antenna pcb board from my amplifier. The amplifier is just a separate eval board, and that picked up and amplified the signal with no input connection/cable attached. Therefore, if the unshielded amplifier pcb can pick up the signal, then it must be getting picked up directly by the traces on the pcb.

Its not enough to just say "it picked up the signal". This isn't surprising at all - ANY conductor is going to pick up some amount of RF. The question is how well is your circuit rejecting the unwanted signal relative to the desired signal. Its not a yes/no situations. Its "is the unwanted signal low enough that it doesn't affect the performance of the system". Again, you are ALWAYS going to pick up some stray signal.

Krenzo posted:

Hmm, I'm not really sure how to explain things differently. My problem is how if you have an antenna that goes to a 3 ghz high pass filter and then to an amplifier. The filter removes all unwanted signals below 3 ghz. If you have an unshielded connection from the filter to the amplifier, then that connection is going to pick up those unwanted signals again and be amplified. They'll end up in the sampled signal. If the connection from the filter to the amplifier is shielded, then no unwanted signals can be picked up between the filter and amplifier because they could only be picked up before the filter which removes them.

I'm trying to shield the connection between the antenna and the various components on the pcb so that only signals are picked up by the antenna.

Right, so you're trying to isolate the post-filtered circuitry from the external RF environment to minimize the re-introduction of noise. I don't know what your design requirements are, but is there any reason you can't use semi-rigid coax to connect your amp/filter/antenna together?

# ¿ Oct 29, 2011 18:25

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

I'm terrible at searching for ICs...I need a 24 or 32 bit latched shift register (5V, ~30mA, I'm just driving some LEDs). There's a bunch of P/Ns that come up in google but none of the usual vendors seem to carry them. I only need one, so preferably something I can get as a sample.

(yeah, I'll just use two 16 bits if it comes to that)

# ¿ Nov 21, 2011 05:54

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

ANIME AKBAR posted:

Check out the AS1105 and related parts. I've used it for driving four digit 7-seg displays, but it can be set up to not do decoding so it can work as a general purpose driver.

Awesome, I picked up a few samples of the AS1107 which can drive 8 7-seg displays.

# ¿ Nov 22, 2011 21:20

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# ¿ May 22, 2024 00:19

Cyril Sneer: Aug 8, 2004; Life would be simple in the forest except for Cyril Sneer. And his life would be simple except for The Raccoons.

ante posted:

The best organization solution seems to be sheets of cardboard in binders with little plastic baggies stapled to them. So you can have a "resistor" binder with each page representing one decade, and each bag on that sheet filled with one value.

Get an Arduino for starters. I'm getting increasingly disdainful of Arduino projects, but it is a good learning tool.
Hobbyists who use them regularly tend to be more concerned with doing things the quick/easy way instead of the "right" way, so try and jump ship to PIC or AVR when you're comfortable. You won't have to bundle a bulky $30 board with everything you make, too.

wait wait wait...you don't have to bundle the board with everything you make. Its just a dev board for an atmel uC. You can just as much have a bulky board with your PIC or AVR.

# ¿ Nov 28, 2011 15:20

The Something Awful Forums > Discussion > Hobbies, Crafts, & Houses > Learning electronics: Release the Magic Blue Smoke

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