Understanding Electronics Basics #1

[Muttley600]

Here's an example that should help demonstrate the "scope" method of frequency determination:

What other method is there beside the multimeter **broken link removed**

OK. We're going to investigate frequency issues for a bit.

**broken link removed** Not that I'm excited or anything you understand **broken link removed**

As to your question, I isolate one, single wave of the sine wave

I've been trying to do that, all I can say is well done **broken link removed** maybe its easier if you export it into a graph **broken link removed**

count the graticules on the scope (10 in this case), multiply the sweep speed (100usec) time by the graticule count (10) to derive a "wave length" of 1 millisecond.

yes, thats a lot easier if you change the scale on graph, how do you know the speed sweep
Edit: ok, gravelrash, sorry graticule, is this the complete box in Volts/div or each segment

Then divide 1 (one) by that number (1 millisecond, as a decimal [0.001]), and get the answer of 1000 Hz, or 1kHz.

seems to make sense, can you sense my hesitation here

For any wave length other than one landing exactly on graticule lines on the scope face is, at best, an approximation.

ok, wavelength, UHF/VHF/AM/FM I take it these are all simply different frequencys known as bands then having secondary frquency in this like you showed me before, but your not talking about that kind of wavelength here are you, you are simply relating to one sinewave

The beauty of an FG is that we can tell it to produce not just one frequency, but cause it to "sweep" across a range of frequencies over a period of time. That is, generate a signal, of a constant amplitude, that, say, starts at 100Hz and increases to, say 10kHz, and then goes back to 100Hz, etc..

That is so cool, shows the spring coil opening & closing perfectly, or is that meant to be....... wow, thats showing me the frequency perfectly
**broken link removed****broken link removed** just don't start me on jam cakes **broken link removed**

Now we'll further adjust the FG: (set "Time" to 5s and "Num" to 20). press the "Sweep" button.

I did that ok, but was struggling to relate to what I was actually changing compared to normal **broken link removed**

Now bring up your scope and observe how the sweeped sine wave appears.Pretty cool. huh?!?

The only thing I can relate this to is walking up a large hill, seeing the crest, getting there to see another one, but then turning around & admiring the view anyway & it's looking ace already, I'm looking forward to climbing higher **broken link removed**

I've never enjoyed learning so much in my whole life

In a bit, I'll post circuits and a lay out on how to use the Signal Analyzer (SG). We will not need the FG for this since the SG has a built-it FG.

Looking forward to moving on, did I mention I was enjoying this

 

[cowboybob]

What other method is there beside the multimeter

If you make a circuit out of a VS, a load and gnd, the multimeter will read the frequency. I don't know the trick, yet, for doing that with any other circuit.

View attachment 62145

yes, thats a lot easier if you change the scale on graph, how do you know the speed sweep

View attachment 62146

ok, wavelength, UHF/VHF/AM/FM I take it these are all simply different frequencys known as bands then having secondary frquency in this like you showed me before, but your not talking about that kind of wavelength here are you, you are simply relating to one sinewave

Yes. Not mixing anything, just one, pure frequency.

I did that ok, but was struggling to relate to what I was actually changing compared to normal

The "Time" you're changing is the total time it takes the FG to complete the frequency "sweep". At the same time, the "Num" is the number of divisions in the "sweep" difference. That is, if you choose to sweep between 100 Hz and 1,000 (1k) Hz (a 900 Hz difference) and choose 9 for the "Num", the FG will put out a 100Hz, then a 200Hz, then a 300Hz (etc. to 900Hz) series of frequency samples. The greater the "Num" number, the smoother the transitions from low to high frequency.

I'm am very pleased that you're enjoying this. I'm enjoying my part also. A lot.

 

[Muttley600]

I'm going to take my time learning this bit as I have a gut feeling it is a very important piece of the jigsaw, I haven't replied to anything else yet as I want to add to my folder as I go, ignoring the math still (don't panic) but what I am starting to understand is the relation to all the different aspects of what we are working with, wilki pages very useful for teaching me what particular words are meaning, I feel when I understand the process then I should be able to relate the math to it at a later date giving me a massive head start over a lot of complicated sums, I'll be able to relate to each letter & symbol meaning I'll know what I'm looking at, meaning the sums will start to make sense

Thanks both for your parts in helping me with this, I can't thank you enough

Goodnight, gotta put fencing up before work tomorrow

 

[KeepItSimpleStupid]

CBB: I was thinking more along the lines of:
A
1) voltage source or SG and 2 resistors in series to ground, say 1K, 9K, 1K
b) The 1K to ground and the voltmeter or scope across the 1K
c) Vary the amplitude

B)
1. Sg connected to a resistor in series with a capacitor
2. Capacitor to ground
3. scope across the capacitor
4. Set Xc = say 10K at 10 Khz , R to 1K K
5. Sweep frequency from 10 Hz to 20 KHz, observe voltage across cap

 

[KeepItSimpleStupid]

Post #318

It's just a minimum length or difference in length in mm (millimeters), nothing more. In essence a tolerance.

Every dimension sent to a machinist needs to have a tolerance associated with it even an aluminum plate. The plate would be a lot more expensive if it was +-0.001". The person working with the component also needs to know this. In this case that dimension might be important to the pick and place machine operator.

Oh, btw I am a a self-taught (with some help) machinist. I had full machine shop privs at one time and that's nothing more than a mechanical drawing.

One lead is longer to also denote polarity and to make it easier to insert. LED's have a long and a short lead too.

 

[cowboybob]

CBB: I was thinking more along the lines of:
A
1) voltage source or SG and 2 resistors in series to ground, say 1K, 9K, 1K
b) The 1K to ground and the voltmeter or scope across the 1K
c) Vary the amplitude

B)
1. Sg connected to a resistor in series with a capacitor
2. Capacitor to ground
3. scope across the capacitor
4. Set Xc = say 10K at 10 Khz , R to 1K K
5. Sweep frequency from 10 Hz to 20 KHz, observe voltage across cap

I'll construct them in the AM.

Thanks for the input, KISS.

CBB

 

[KeepItSimpleStupid]

Methods of determining frequency

1. Frequency counter (high accuracy)
2. A scope (low accuracy)
3. Scope with math functions
4. Scope with cursors (like the sim's)

 

[Muttley600]

Fencing done just in time for work, back to electronics tonight

 

[cowboybob]

KISS,

Assuming this:

Capacitive reactance is an opposition to the change of voltage on a element.

and, since LateX is still not working, this: X[SUB]c[/SUB]=-1/ωC=-1/2(3.14)fC

Is this (dB example): View attachment 62179 ?

Or this (V gain example): View attachment 62180 ?

Or neither, what you were looking for?

What say you?

I'm thinking demo of frequency effect on reactance of a resistor (no reactance, of course. Just plain old division goin' on.) as shown here:

View attachment 62181

 

[KeepItSimpleStupid]

They both work, but now we have to teach what a db and logs are? Darn math. The RC product is tiny so the frequencies are higher where this occurs.

15,915,494.58 Hz = 1/(2*3.14159 * 1e-12 uF * 10,000 Ohms)

In any event, we can predict the frequency where the output is 70.7%, 0.707 (really the sqrt(2) decimal or -3db down from the beginning of the sweep.

I did something totally absurd here, by using way too many decimal places on purpose. The capacitance in a real circuit could have a +-5% tolerance and the resistor a 5%, 1% or lower tolerance, thus the number of digits I calculated to doesn't make any sense.

The point here is, that resistors can divide voltages at all frequencies and the voltage across a capacitor is frequency dependent.

The graphs look funny because they are on a log scale. Earthquake magnitudes are on a log scale. e.g. a 4 on the Richter scale is 10 X more powerful than a 3 on the Richter scale and a 5 is 100 times more powerful than a 3.

Logs have bases. The two common ones are Log base 10 and log base e, usually denoted by LOG10(x) and LOG(x).

 

[cowboybob]

Graham,

They both work, but now we have to teach what a db and logs are? Darn math.

(My emphasis)

There's a reason for using LOG scales. Look below and tell us which graph is better at depicting the effect of frequency on the reactance of a capacitor?

LOG frequency scale: View attachment 62189 Linear frequencyScaleView attachment 62192

In my mind, the LOG frequency scale does a better job (than the Linear scale) of showing how a capacitor "reacts" (opposes voltage) to an increasing frequency. Just my opinion. Either scale shows the exact same thing, just differently.

Also notice how the LOG Scale example emulates the shape of a sine wave.

ALL this stuff, eventually, ties together in a nice, neat package.

That's where the math comes in.

If you look closely at the way the LOG scale is divided, you may see the method to the madness.

Whatever the case, You're still going to have to learn what a LOG scale is.

dB is another issue. But that, too, will eventually have to be learned.

Or at least, in both cases, understood.

 

[KeepItSimpleStupid]

Log10(x) is easy. It's just the exponent.

Number    LOG10      10^ number     alternate calc        
1                0             1                     0
10              1              10                  10
100            2              100                 10*10
1000          3              1000               10*10*10
10000        4              10000             10*10*10*10

The tags should have preserved the spaces of the table, but it didn't. There may be a TABLE tag of some sort.

Any number raised to the 0 power is 1. It's just a definition.

LOG base 10 of 25 is 1.397940009
LOG base 10 of 50 is 1.698970004 which is a number between 1 and 2.
LOG base 10 of 90 is 1.954242509
LOG base 10 of 99 is 1.995635195 (nearly 2)


The LOG function is not defined for 0 or negative numbers.

The graph is read almost the same way as a linear graph. In the graph above there are 10 divisions between 1.00M and 10.00M. Finding the value between tick marks is called interpolation and that's much harder.

 

[KeepItSimpleStupid]

Where did you see the db reference before?

If you ever bought a high-end stereo, then you may have seen things like a frequency response between 0 and 100 kHz, +0, -1 db.

If the frequency response if stated as 20-20,000 Hz, then it's assumed that the -3db point is at 20,000 Hz. This means that the output at 20,000 Hz is about 70.7% of wat it was at 20 Hz.

Oh, and since we are doing simple math. 100% is equal to 1 and 50% is equal to 0.5. A percentage converted to a number is percentage/100.

I don't really want to diverge into a discussion about db yet, but some caveats are that db has to have a reference level. In electronics, there are both voltage and power references.

dbV is db referenced to 1 volt.
dbmV is referenced to 1 mV

db in CBB's example is referenced to gain or amplification. 0 db is no amplification. The cool part with db is when you have a multistage amplifier, gains in db are simply added. You don't have to multiply the linear gain of each stage.

It's also useful when designing a TV distribution system for the home. There you can easily see that if you had to multiply, things get messy. Coax has a loss per some length and is frequency dependent because of the capacitance of the coax.

db is also used for power. dbmW would be referenced to 1 milliwatt etc.

 

[Muttley600]

Don't panic guys, I haven't got lost long day at work, last one tomorrow then week off again.......yippee
Lots of catching up I see & the easy bit after quick flick through

Thanks for showing me I'm a numpty KISS...haha, leads-15/5 is just the minimum length

Be on computer shortly

 

[KeepItSimpleStupid]

numty - I had to look that one up.

All is not lost. You learned that units are important. e.g. 15 mm or 5 mm not 15 uF and 5 uF or whatever. That's an important lesson. I learned it too. You could loose a large number of points on an exam if you didn't put units to the answer or they were the incorrect units. If you knew the units were mm, then you would have had "A magnificent grasp of the obvious" kind of moment. There is the old cliche When you Assume, you make an a$$ (out of)-U (and) Me.

 

[Muttley600]

Didn't get chance to get on computer tonight, Lou has turned into puter hog......damn, we've both got the same bad habits.lol
Still been catching up on reading about stuff, just need folder on there to put all this knowledge into
Will catch up properly tomorrow

Night both

 

[Muttley600]

I'm back & have loads of time **broken link removed**

Please forgive how far I am behind, I have a bit of catching up to do

The MAX Ripple it can stomach without blowing up is 175 mA RMS (milliamps root mean squared)

Does that mean 175x175= 30625mA - 30.625A, that seems a lot if I have that right **broken link removed**

A topic that hasn't been covered at all and needs some time devoted to it. Z is impedance. The units of Z is in ohms. It is frequency dependent.

No, not covered yet but I can know tell you that I know impedance is frequency related, oppistion to circuit as part of magnitude (don't know what that is yet) & phase (relax, I get that bit **broken link removed**)

This particular capacitor is suitable for use in switching power supplies.

ok, quick guess, thats why it takes a moment for the led to go off after turning off supply i.e. soldering iron supply?

Please don't answer any questions I ask if you have covered them since post #312 but feel free to answer any that you haven't covered & I'll catch up with answers as I go

Great to be back

 

[Muttley600]

For capacitors: The higher the frequency, the less charge will accumulate and the smaller the opposition to the current.

For inductors: [an increase in] frequency [Or, the greater the opposition to the current

Notice the difference between the two (as to current levels) with an increase in frequency. These opposite reactions are important to remember.

Well, with KISS's original info about these both having the ability to change things but not instantly (you did tell me to remeber that bit, god knows how but it stayed firmly in my brain)
& your info, I'm slowly building a little picture in my head, now thats how to learn, in stages **broken link removed**

Edit: I'm up to post #317 already **broken link removed**

 

[Muttley600]

Note the various SG settings.

How did you get 128 resolution, I can't go above 100 **broken link removed**

What was your VG set at CBB

Just going to nip & get some tobacco, this could be a long night
Can stop panicking about running out in middle of night now.lol

 

[KeepItSimpleStupid]

I'm back & have loads of time **broken link removed**

Please forgive how far I am behind, I have a bit of catching up to do

Does that mean 175x175= 30625mA - 30.625A, that seems a lot if I have that right **broken link removed**

No, not covered yet but I can know tell you that I know impedance is frequency related, oppistion to circuit as part of magnitude (don't know what that is yet) & phase (relax, I get that bit **broken link removed**)

Nope.. Remember that RMS is a measuring technique. You don't do it after the fact. e.g. if you had a unit sq ft, you wouldn't have a unit (sq ft sq meters).

ok, quick guess, thats why it takes a moment for the led to go off after turning off supply i.e. soldering iron supply?

Wrong again. It just means that the capacitor is suitable for removing ripple at higher frequency such as 100 kHz or more which is where switching power supplies operate. The filter caps that used at 50 or 60 Hz sometimes aren't suitable for use at higher frequencies.

Capacitors do store a fair amount of energy and thus can delay the turn off of the soldering station.
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