How to generate a rotating line on CRO (Cathode Ray Oscilloscope)?

Hi all,

Iam trying to figure out how to generate a rotating line on the CRO.

To be more specific, the signal I require is like the second hand of a clock, but moving continuosly instead of discrete steps. This output must be obtained as the XY Transfer characteristic plot.

My assumption is that the signal is a continuosly phase varying one owing to it's rotation. But I cannot think of anyway to generate one.

Please help me out.

Dear Rahul,

Just enter at XY oscilloscope input with a sinusoidal with phase zero between them.

Best regards

I think the signals need to be 90 degrees out of phase....

Mr. Pruitt,

You are right, a zero phase will draw a straight line from 3rd to 1st quadrants.

Thankyou by your attention.

No, he said "Rotating line...like the second hand of a clock." So, think of it this way: A scope, in it's common (i.e. usual) mode, generates a horizontal line. How does it do that? With a sawtooth voltage on the X axis that has just enough amplitude to sweep the beam the full width of the display area (or typically a large percentage of it).

Now, if you put the scope in X-Y mode, and do the same: apply a sawtooth wave of the proper amplitude (call it V) to the X input (with the Y input at zero), again you will get a horizontal line. If you add a similar waveform (same frequency, phase and amplitude) to the Y input, you'll get a line that is at a 45 degree angle. And if you remove the waveform from the X input (so it stays at 0 Volts), then you'll get vertical line. The frequency of the waveform is uncritical and only needs to be high enough to engage the persistence of the screen phosphor so there is no flicker --on my scope that's around a minimum of 1kHz.

To make this more like a clock second hand, move the line to the center of the screen (i.e. translate the coordinates to the center of the screen), by calling (V/2,V/2) the origin and vary the amplitudes of the two waveforms (each running a around 1kHz or above) at a rate that will rotate the line at the speed that you want, from V/2 to V back to V/2 then to 0 and back to V/2 with a 90 degree lag between the two. The function of the variance is sinusoidal.

So, that would look like this:
* Starting at 12 o'Clock:
Y is swept [by a sawtooth wave] from V/2 to V at 1kHz (i.e. a 1kHz sawtooth wave with amplitude extents of V/2 to V)
X is at V/2 with a zero amplitude.
* 1 o'Clock
Y has an amplitude extent of V/2 to V/2 + (V/2)(sin60)
X has an amplitude extent of V/2 to V/2 + (V/2)(cos60)
* 2 o'Clock
Y has an amplitude extent of V/2 to V/2 + (V/2)(sin30)
X has an amplitude extent of V/2 to V/2 + (V/2)(cos30)
* 3 o'Clock
Y is at V/2 with a zero amplitude.
X has an amplitude extent of V/2 to V
* 4 o'Clock
Y has an amplitude extent of V/2 to V/2 - (V/2)(sin30)
X has an amplitude extent of V/2 to V/2 + (V/2)(cos30)

and so on...to make this smooth, simply vary the extents smoothly, rather than in steps (as shown, above). Note: I only showed it in clock face steps to get the idea across of how the waveforms change

Given hie=2.4kohm hfe=100 hre=4x10-4 and hoe 25mcroSiemens, SKETCH:

a)common emiter hybrid equiv model
b)common emiter re equivalent model
c)common base hybrid equivalent model
d) commong base re equivalent model

Whatever rotates yer beam, man.

Thank You all for your replies. :)

Steve Lawson Sir,

Thank you for your idea of using a sinusoidal amplitude variation to implement the rotation. Hadn't thought of that. I was thinking about a signal whose phase keeps varying continuosly. You idea of amplitude variation is simpler and practical.

Can you also give me a circuitry to generate the amplitude varying signal?

(My idea for the circuit is to generate sine wave , multiply it with the sawtooth wave and apply to Y channel, then generate a cosine wave, multiply it with the same sawtooth and apply to X channel. But, how can I multiply the two signals? )

Thank you for all your replies Sirs. :)

The line can be obtained using the sinusoids, preferably a half wave rectified sine wave (to resemble a second hand on a clock) , but I wanted to get the line rotating.

Hi,

Will these waveforms generate the necessary pattern in XY mode? They are basically sine modulated sine waves. :)

The waveforms were drawn roughly in paint so please excuse the inaccuracies. :)

And if yes, please tell me how to generate such a waveform. :)

Thank You.

Whew! Been awhile since I played around with analog signal multiplication. I'm not even sure if the ICs I used are even still available (most of the world has gone to digital ;)

I, personally, would do it with an MCU and a couple of DACs.

But if you want to go analog, there's some fragments of info that might help:

After some surfing on this topic, I hit upon this:
* http://forum.allaboutcircuits.com/showthread.php?t=58162
Which uses this:
* LM13700
Which _is_ available.
Also check out:
* http://www5b.biglobe.ne.jp/~houshu/synth/ (scroll down to "VCA")

From another forum:
"> It's much easier to use a LM319 -or similar op collector- comparator
> and a TDA7052B (amplifier with a DC-gain control) to build a circuit
> like this.
>

Or to use a MC3340 electronic attenuator
or even better the NE572 compandor with built-in rectifier, separate
attack/release time and low distorsion."

I used to use the MC1494, but I don't think those are available anymore (perhaps on eBay?)
Information and possible source for the MC1494:
* http://www.onsemi.com/PowerSolutions/product.do?id=MC1494
* http://www.arcadechips.com/product_info.php?m...d=101&osCsid=ed2b3d8042e123662f4fe60a7a00d294

Or there's the CA3080, but that appears to be out of production, also (again, perhaps eBay):
* http://www.intersil.com/en/products/amplifier...buffers/all-amplifiers/amplifiers/CA3080.html

So, try looking for "Operational Transconductance Amplifiers" [OTA] or a DC amplifier with DC gain control or Voltage Controlled Amplifier [VCA] circuits/ICs for analog synth.

This might give you some ideas:
* http://forum.allaboutcircuits.com/showthread.php?t=58162

Your drawing didn't show (only GIF [.gif], JPEG [.jpg] and PNG [.png] will work).

BUT, the shape of the wave form can be anything that sweeps the beam across the screen. A "sine modulated sine wave will work, but a sawtooth waveform will produce the most even line.

On my MCU comment, even simpler might be using an MCU with two PWM outputs with a low-pass filter on each (e.g. resistor/capacitor).

Sir,

Thank You for all those links. My friend suggested to me that using an AM wave (sine modulated sine) with alternate positive and negative half cycles, and the same wave 90 degree shifted will give the result.

This is the waveform we need to generate.

http://www.youtube.com/watch?v=pewdx8rGrkM

We've got an idea on how to generate it, except for the rotating line. We cant try out your idea till tomorrow, since our lab is free only then.

OK, now I get the picture -- you didn't tell me there are Rules--one of them being, no programmable components--so, disregard my MPU suggestion [and also only 2 members to a team, so it seems to me that asking our advice is a violation, but that's for you to sort out]!

Yes indeed, "Amplitude Modulation" is another term for what I have described. But, in my case, I suggested using a sawtooth carrier wave, modulated by a low frequency sinewave. The carrier would be around 1kHz or above, and the modulating wave looks like around 1Hz.

The modulating wave for the X input would be 90degrees out of phase with the modulating wave for the Y input.

If the two supplied "Signal Generators" can produce a sine wave at around 1Hz and if the phase of the output waveform can be controlled, then they could supply the two modulating waveforms and a sawtooth wave is very easy to generate with op-amps.

So, all you need is a modulating circuit. That is basically an analog multiplier (or voltage controlled amplifier). I'm guessing you will need to achieve this with discrete components, which can be done or you could use an IC, such as the LM13700.

You will, also, need to do some voltage translation as I described before.

If none of the suggestions, in previous posts, will work for the Modulating circuit, then try the following Google searches:

* VCA
* Voltage Controlled Amplifier
* Operational Transconductance Amplifier
* Analog multiplier
* Electronic attenuator
and try adding the term "discrete" or "with transistors" or "IC", etc, to the search.

Thank You for the reply Sir.

My friend did independently figure out the waveforms required, and hopefully we will be able to implement it in our lab tomorrow.

Thank You a lot for your time and help. I'll let you know of the result.