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.

I know it can be expensive, but anyone interested in this stuff should really try to get ahold of an oscilliscope and a function generator. It greatly enhances everything you might want to do.

Oh, and all this piddly digital/LED/microncontroller stuff is boring. You guys need to try some real electronics:

https://www.pupman.com

Although, fair enough, perhaps that's not exactly for someone just learning electronics...

# ¿ Jan 9, 2008 00:51

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# ¿ May 1, 2024 00:07

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 love watching engineers engaged in debate

# ¿ Jan 11, 2008 04:12

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.

Cuw posted:

Digital ROCKS!

*sigh*

ah well, maybe with everyone focusing on digital subjects these days, there'll be more jobs for us RF people.

# ¿ Jan 12, 2008 16:23

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 know where I could order a whole lot of LEDs (like at least 100) for cheap?

# ¿ Jul 13, 2008 04:53

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.

There's an electronics surplus place nearby that I like to visit; it has several large boxes full of old vacuum tubes (Sylvania, Philips, etc). I'd love to build a tube-related project but I have no idea how to identify what tubes might be useful.

Short of taking note of each and every tube variety, is there a way I can learn about different tube specs, and what ones are generally considered "useful"?

# ¿ Sep 14, 2008 03:43

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.

Grand_High_Took posted:

I'd like to build a small and easily concealed electromagnet in order to trigger the induction based detector that sends a "car exiting" signal to the gate outside my apartment.

The gate system is manufactured by Elite access systems inc, and the model # is SL-3000-UL.
The manual is here: http://www.amazinggates.com/Do_It_Yourself/web/Manuals/Elite-SL_3000-manual.pdf, mostly useful for page 22, which shows a diagram of the induction coil, or loop, or whatever they're calling it.

Actually, for those not interested in the whole PDF, here's the picture:

I understand from a neighbor that a bicycle contains enough metal to trigger the thing, so if I can generate the same amount of magnetic fluctuation in the field generated by their coil as is caused by the amount of metal in your average bicycle, that should be sufficient.

My question is: how much power do I need for this, and how big is the electromagnet going to have to be? I want to have something small enough that if I paint it black and put it in the driveway with a dollop of tar over it, no one will be very likely to notice its presence. Is this feasible?

Any input would be most appreciated.

Such a device is likely not possible.

The electronics are likely callibrated so that a shift in inductance (or impedance, or current, or voltage, or resonant frequency - these are all equivalent effects) above a certain threshold is considered a "detection". From that, one can calculate how much voltage (or current) the detector loop must see. We know the area of the detector loop, so we could deduce how much external field must be present to induce the necessary voltage. Finally, if we posit the device to be placed on the ceiling of the garage, we can determine what kind of power we'd need in order to produce a sufficiently strong field.

# ¿ Jan 3, 2009 20:58

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.

It's technically possible, but not likely to be practical - moreover, designing a solution would require more information on how the detector works (frequency and power, roughly, would be nice).

Basically, you need pick an operating frequency for your transmitter then calculate how much power would be needed to induce a sufficiently-noticable change in voltage across the detector loop.

# ¿ Jan 5, 2009 05:14

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.

babyeatingpsychopath posted:

I think a bulk tape eraser (reasonably large AC electromagnet) sitting on the coil would work fine. Probably a 5lb lump of soft iron with a few hundred turns of wire on it and a few amps DC at 12V would induce more of a field than a bicycle would.

Try a few different orientations. Really depends on how far away the thing is. I see that it's 4' from the edge of the road, plus width of sidewalk, so like 8' away, probably. I think this is a great project to just start making stuff and seeing if anything works, and from how far.

That's pretty much exactly what he'd have to do - just start making stuff and see if it works. But I was thinking this was something he was going to try and bury/hide - and I'm not sure a big lump of iron with, a few hundred turns, and a several-amped power supply would suit this purpose.

edit: We need more RF talk

# ¿ Jan 6, 2009 00:51

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.

Cross_ posted:

Has anyone here experience with metal detector circuits or capacitance sensors ?
I am trying to add a sensor to my project in order to detect the presence of a metallic object above an electrode. The electrode should be ca. 3" x 3" and detection distance should be up to 1".
The past two weeks I have been playing around with an Omron B6TS capacitance sensor but unfortunately could not get the SPI to work properly even though the design looked nice. Basically I am looking for a replacement with somewhat increased sensitivity. Any recommendations ?

Do you need a capacitance sensor specifically? That is, could you build the electronics yourself? I would think you could build an oscillator based on the self-capacitance (and whatever stray capacitances are around it) of the electrode itself and run this through a comparator tied to a known frequency. With some callibration you should be able to correlate the output level of the comparator to the shift in capacitance induced by your metallic object. This would all take a bit of experimentation, but its a nice "quick and dirty" method.

# ¿ Jan 20, 2009 03:43

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.

Cross_ posted:

With this out of the way I am curious how your approach would work. Are you suggesting an RC/LC oscillator and then measuring the phase/frequency shift induced in the capacitor or coil? Would that provide improved resolution compared to the timing method above?

Yes, an LC oscillator. Measure the frequency shift by comparing it to a local oscillator set to the unloaded resonant frequency (it doesn't have to be super precise). You'll get a DC level output that varies according to magnitude of the frequency difference. Monitor this output with a scope as you bring your metallic object near and take note of what it reads when you get to 1". Provide this voltage to level comparator (something that spits out a 1 or 0 depending on a voltage threshold - I can't think of the proper name). You could put potentiometers on DC sources for adjustment/calibration.

# ¿ Jan 22, 2009 02:11

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.

Okay guys, a big one for ya. Wasn't sure if I should start this as another thread, but here goes.

I recently picked up this LED matrix at a surplus shop:

The only problem is I have no idea how to drive it. I've played around with it a bit and made a few discoveries. I've managed to at least figure out how the LEDs are arranged:

The entire matrix is split into a 2x8 grid, with each cell containing 8x4 (ie, 32) LEDs. Power is supplied to each column by one of the 8 power transistors on the left (you can see the thick traces running from left to right). The LEDs in a given cell are then wired to the bank of resistors (circled, on the left). LEDs along the bottom half (Row B) are wired to the lower 32 resistors. LEDs in the top half (Row A) are wired to the top 32 resistors. So, for example, if one were to apply voltage to the central pad of column 6, the LEDs in cell B6 would be illuminated sequentially by sweeping a ground connection along the bottom 32 resistors. The LEDs in cell A6 would be illuminated sequentially by sweeping a ground connection along the top 32 resistors.

Each of resistors, all 64 of them, are wired to 8 UCN5821 chips each with 8 outputs (8 x 8 = 64).

Here is a close-up of the logic circuitry:

Here the connections between the LEDs, resistors, and UCN5821 chips is clear. The ICs present are as follows:

UCN5821: 8-bit serial latch
AM26LS31: Quadruple differential line driver
SN74LS15: 3-input AND gate
M74HC238: 3-to-8 decoder.

I'm an RF guy, not a digital guy, so this is all pretty foreign to me. I basically understand everything up the UCN5821s. I have no idea how to feed data into this or how to clock it. I'm hoping that it might resemble some sort of "standard" LED matrix architecture.

Help me out guys! I really want to get one working - there are a whole lot more where this one came from!

I will provide as much additional information as requested.

Cyril Sneer fucked around with this message at 06:47 on Feb 28, 2009

# ¿ Feb 28, 2009 06:43

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.

Mill Town posted:

That looks like the LED sign that the guys at hacklab.to recently reverse-engineered. Informative blog post here:
http://www.andrewkilpatrick.org/blog/?page_id=795

Also try their IRC channel at #hacklabto on Freenode if you have more questions.

Edit: Did you get that at Active Surplus?

My god, thats EXACTLY what I'm trying to do. And yes, I did get it at Active Surplus. Looks like I'll be emptying their stock tomorrow

# ¿ Mar 1, 2009 01:25

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.

Picked up another 6 of those panels. Hope they all work - this is gonna be a wicked project.

# ¿ Mar 1, 2009 21:52

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.

I'm having trouble understanding the purpose of FPGAs, and to what sort of problems they are applied.

With a microcontroller, the hardware stuff is already taken care of and you just have to focus on programming the thing.

If a microcontroller is lacking in functionality, why not just use an embedded processor or a PC?

I apologize for the naivety of this question.

# ¿ Mar 12, 2009 06:37

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.

catbread.jpg posted:

Mr Anime, what classes are you taking exactly? It sounds like a strange program. I'm really glad of the really broad 200 level program at my university, we were programming AVRs off parallel ports (with hand-soldered parallel port connectors that fell apart at a gust of wind because of clumsy soldering...), as well as getting a good grounding in electronics, power systems, signal processing, and software development.

I've been planning to specialise fairly early on, and it's worked out pretty well.

This year, 400 level:

Power engineering applications (nitty gritty power engineering, turbine governors, system planning etc.)
Power systems (power system analysis, load flow, protection)
Power electronics II (focus this year is on HF switching converters)
Computer hardware (more micros, FPGAs, and DSPs)
Engineering management (cynical marketing inside)
Project (sweetness)

The synergy between power, power electronics, and hardware is really cool, I'm glad I chose it. With any probability, I'll be working in power engineering in the consulting sector, but it's good to know that I could easily go into power electronics if I wanted.

Jesus christ. Does nobody study RF/E&M anymore?

# ¿ Mar 18, 2009 04:39

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.

Twerpling posted:

I did and I actually specialized in it. That being said, I was the only one in my class of 60 or so to take all the E&M/RF/Optics courses. Everyone else went for the electronic or programming tracks.

I specialized in it as well. Your description sounds exactly like my experience; they've cancelled a bunch of courses too because not enough people signed up for them (I complained bitterly about that).

# ¿ Mar 18, 2009 14:21

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.

Sorry, your meter won't work for testing caps.

The left green region is for measuring resistance.
The left white region is for measuring DC voltage.
The right white region is for measuring AC voltage.
The right green region is for measuring DC current.

Your meter can also test diodes and transistors, but I doubt you'd have a use for that.

# ¿ Apr 2, 2009 01:52

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.

I'm having a problem sourcing a common connector.

DigiKey and Mouser both offer these headers:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A1927-ND

that's the 640457-4 and the 640457-5. These are 4-position and 5-position headers.

However I'm having a hell of a time finding the appropriate mating piece on either site. DK lists the mating products, and it seems like 644512-4 is the appropriate one, except its listed as non-stock. Indeed, this is the case for both DK and mouser!

Why would they carry the header but not the connector?

Do any of you guys know where I could find the appropriate connector for the 640457-4/5 header? It's a pretty common part!

# ¿ Apr 13, 2009 02:25

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.

Scarboy posted:

crimping tool for 580 dollars!

Are crimp tools patented or something? Why doesn't someone start a company mass-producing these things and selling them for cheap?

# ¿ Jun 16, 2009 04:36

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.

turbo sex bat 4000 posted:

Because a cheap crimping tool is called a pair of needle-nose pliers.

It is kind of ridiculous but if you ever have to do more than a hundred crimp connections in a day it makes sense. You have to be able to rely on the connections you make.

That doesn't address my question. I'm well aware of the need for crimp tools. My point is that I don't see why they can't be mass produced and sold for much cheaper.

# ¿ Jun 17, 2009 14:49

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.

SnoPuppy posted:

Probably because the hobbyist market isn't their target? I'm sure most sales go to companies, who don't really care that much about footing the bill for a $500 crimp tool.

It's the same reason why a flight on Monday morning is expensive - that's when business travelers like to fly, and airlines know that their companies will pay.

The hobbiest market doesn't have to be there target. It isn't that companies don't care about the cost, its that they have no other choice. If I could sell the same crimp tool for $100, guess who would get the (and every) sale.

Monday flights are expensive because the demand is high.

# ¿ Jun 20, 2009 15:43

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 know EagleCAD really well?

All I want to do is flip/mirror a board. The built-in mirror function mirrors about the top and bottom sides - that is not what I want. I simply want to mirror the board about the Y-axis (ie, flip the left and right)

I have been completely unable to locate any such function to perform this, which is leaving me frustrated as its such a seemingly simple task.

# ¿ Jun 25, 2009 14:40

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 not quite as simple as it seems. Mirroring each part (while keeping them on the same side of the board) would result in footprints that don't match up with the original; essentially making them entirely new parts.

Keep in mind that for most designs, doing what you're describing would make the board completely useless, since any device whose footprint isn't symmetrical about the flipped axis would not work on the flipped layout. Are you sure this doesn't apply to your design?

I don't quite follow. If I take a graphical image of the board and mirror it in a grahpics program, it looks just how I want it to look.

# ¿ Jun 26, 2009 13:15

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.

Hillridge posted:

What's on the board?

He's saying that if you mirror the board, you will also mirror any footprints. For parts like ICs, this will mess up all the connections. The numbers below are the pins on an 8 pin IC, the dotted line is what they mirror over:
code:
1 8 | 8 1
2 7 | 7 2
3 6 | 6 3
4 5 | 5 4
You can't mirror the physical part, so when you solder it to the mirrored board, all the connections will be wrong.

There are a few cases of simple boards where this may not be true though, which is why I wonder what your board looks like.

Ah, right, there are no ICs on the board, just a bunch of passive stuff.

The mirror command in the board layout just swaps top/bottom layers. It doesn't mirror about an axis.

# ¿ Jun 27, 2009 00:29

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:

There's actually a senior EE I answer to, and when I told him the demands were realistic he basically said "oh come on, where's your sense of adventure!" or some such bullshit. I'm literally the only person in the entire company who can interpret the paper's methodology, and it absolutely supports my objections. I'm basically going to end up turning in a 30 page report spelling out in terms they can understand that they've been wasting both my and their time.

That senior EE was right. That's a fun sounding project. I'd love an excuse to play around with something like that. Who cares if the end product will actually work or not? You'll learn a lot and it'll be neat.

# ¿ Jul 7, 2009 03:23

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:

magnetizing inductance approximately follows the inverse cube for distances much greater than the radius of each coil.

So you're working in the far-field. Use high frequencies and a non-omni-directional antenna.

Cyril Sneer fucked around with this message at 04:39 on Jul 8, 2009

# ¿ Jul 8, 2009 04:36

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:

no, it's midrange field coupling, not radiating.

here's one version of the paper itself.

Your boss just wants some kind of long distance power transmission scheme; he's not expecting a replication of the paper - he just thought it might be useful to that purpose.

# ¿ Jul 8, 2009 14:27

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.

SnoPuppy posted:

Right, the method which your boss suggested can't be done. However it seems like the real problem is "send power". Which is further restricted to "send power without wires." Which is further restricted to "send power without wire using method x."

If the most restricted version can't be done ("using method x"), investigate the next level up and present those findings. If that can't be done, go even further up the chain, until you have a solution. Realize that sometimes people ask the wrong question, but it's still up to you to give the right answer.

That way you're not the guy that can't solve problems, you're the guy that gives answers.

Yes, this. The overall point here is that telling your boss "it can't be done" just does not come off well. A good engineer should always be able to finagle a solution at some level.

# ¿ Jul 9, 2009 00:23

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.

https://www.pupman.com

Look up what the tesla guys do on their solid state coils. Zero-triggered crossings with long ring-downs at very high power are exactly what they design for.

# ¿ Jul 14, 2009 15:18

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'm well aware of how solid state tesla coils work. After all I just finished helping some classmates build a one megavolt musical coil for the cleveland ingenuity festival. It used class E amplifiers in a split-phase configuration (based roughly off of steve ward's techniques), but that's not plausible for this application.

How about instead of saying everything is impossible, tell us what exactly the distance requirements are (and WHY they are what they are), and what exactly it is that needs to be powered remotely.

# ¿ Jul 15, 2009 03:44

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.

Why does the efficiency have to be 10%?

# ¿ Jul 15, 2009 14:37

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:

Eh, the more I think about it the more apparent it is that I'm going to have to settle for just driving the series resonant tank with a square wave. Class E amps require switches that are both low resistance and tolerate high voltages, which isn't feasible at the frequencies I'm dealing with. At least with square wave drive I don't need to worry about the voltage requirements. Just need to find good FETs with very low losses.

What frequencies are you working at?

Again, the solid state tesla coil guys operate in the ~100s kHz range.

# ¿ Jul 20, 2009 02:40

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 feel dumb for not knowing this, but could someone elucidate the differences between small signal transistor circuits versus large signal, ie, power amplifier transistor circuits?

I'm looking at my electronic devices textbook and I don't really understand why small-signal circuits are in one chapter and power circuits - where they introduce class A, B, C amplifiers - are in another. It seems like an artificial distinction.

I mean, I can build a voltage-divider bias circuit and stick a power transistor in it, can't I?

Conversely, the power circuits all look like small-signal circuits, except they stick transformers in various places and call them by different names.

# ¿ Nov 6, 2009 05:10

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 playing around with a class-E amplifier and need a good switching FET to use. I don't know much about the common FETs; I need something that can handle about 1W - 2W and has good switch-like characteristics (ie, high impedance when off, very low impedance when on). The lower the required gate drive the better.

clredwolf posted:

Anyone know where to find a crapload of enamel wire cheap? Time to make a big sparky thing.

(Friend of mine and I decided to work on a Mini-SSTC, and then turn it into a computer-controlled sparky thing.)

Check ebay. Always tons of magnet wire.

# ¿ Nov 29, 2009 22:16

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.

64 MHz, Low Rds.

# ¿ Dec 2, 2009 00:54

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.

I suppose those are what I'd want to pick from. Lower forward current is better. Blocking voltage maybe 10 volts.

# ¿ Dec 2, 2009 14:57

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.

64 MHz! I know they exist...

Hard-switched, N-channel, load current say, ~200 mA.

# ¿ Dec 3, 2009 05:26

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.

catbread.jpg posted:

You should definitely read this.

http://focus.ti.com/lit/ml/slup169/slup169.pdf

And then you should tell me why you want to switch at 64 MHz! A 15.6 ns period is certainly interesting.

http://www.ixysrf.com/products/switch_mode.html

http://www.ixysrf.com/pdf/switch_mode/de150_101n09a.pdf

This will probably do what you want, if somewhat over-specced, good luck with the drive circuitry! It's 'rated' for 100 MHz operation, but note the combined rise and fall times (with perfect drive circuitry) are 8 ns. Fortunately your load current is low enough, as the switching losses will probably be in the order of 1W (10V * 200ma * 1/2)

Thanks. You posted this a while back but I haven't had time to review it.

ANIME AKBAR posted:

I still don't know why people bother with pspice or ngspice when ltspice is much more user friendly and equally functional.

Microcap is even better.

Cyril Sneer fucked around with this message at 06:19 on Dec 16, 2009

# ¿ Dec 16, 2009 06:05

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.

Just picked up a 350 MHz 4-channel Tektronix scope off eBay. Merry Christmas Cyril Sneer! :cool:

# ¿ Dec 21, 2009 05:00

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# ¿ May 1, 2024 00:07

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:

- I used a calculator to figure out the size of the 50 ohm trace for my particular pcb board type and it did not seem to take into account the length of the strip.. so length doesn't matter? Only width and the strip's distance to grounding planes? What is the 50 ohms referring to? Why is 50 ohms such a popular value too? I have searched around and can't find a solid explanation for this.

What you are building is a type of transmission line, which is composed of (or modelled with) repeating units of inductors, capacitors and resistors. The values for each component give rise to what is called the characteristic impedance of the line. You only care about the per-unit values, as the physical length of the line is modelled by a long chain of the single unit circuit. If you look up the circuit model for a transmission line, this will make much more sense.

The 50-ohms is referring to the characterisic impedance of the strip. That is, the impedance seen by the source or load connected to the strip.

50-ohms is special because its the characteristic impedance that is achieved in coax cable when using 'reasonable' sized dielectic and conductor sizes in consideration of power dissipation. There is nothing intrinsically special about the value - it just works well in terms of the materials used in coax cable.

macpod posted:

-Is it normal to have the ground plane for the rf signal be the same ground used by all other digital signals or should this have been separated. From reading around it seems it is fine to join them.. but in the past it was preferred to use more than one plane.

I'm an RF engineer, and general practice is to keep them separate. It is a much-debated topic though, as sooner or later, the grounds will be tied together. I think the more important point is to make sure your digital supply lines are all filtered (series chokes, caps to ground).

# ¿ Jan 2, 2010 07:21

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