Recent Posts

1

Projects, Designs, and Technical Stuff / Re: Using a current output DAC to control laser diode brightness: which IC to use?

« Last post by phennessey on Today at 11:23:46 pm »

But still, why a period of 1MHz?  You can more easily pulse it at a few kHz and vary the duty.

This laser is being used to expose a light-sensitive material very quickly, so I need the pulses to be real-time, and at 1MHz rate. PWM won't work.

2

Test Equipment / Re: Choosing between entry-level 12-bit DSOs

« Last post by tggzzz on Today at 11:21:12 pm »

looking for "credential", i found an example how BW limited scope can miss things out... you can quick read the possibly fabricated story until the Analog Discovery "recommended for beginners" screen capture... how it missed 96MHz oscillation... the fix? (or verification) use SA (probably an expensive one) and a 300MHz scope... so the conclusion? if you want to see oscillation or something wrong in your circuit, get a SA and 3x the suspected oscillation freq DSO... so for example... if oscillation is at 300MHz, get a 1GHz DSO (and SA too and other TEs mumbo jumbo) one... thats the (spending) more, for less (novel or fancy technique work) just as we typically did or recommended Practical Traps with a One Transistor Audio Amplifier, Solderless Breadboards, and Oscilloscopes unless your name is Jim William, your tin can novel technique will be commonly accepted as crap by professionals (or retired there is)... ymmv.
...
what could possibly go wrong with emitter follower on breadboard unless purposely impedance mismatch at long input lead, no?
...

A few points about that rant:

• that is a complete misrepresentation of the article, in too many ways to bother to describe. I will leave other people to infer reasons for that misrepresentation
• what is the benefit of make it difficult to read?
• the few technical points are wrong: it is nothing to do with DSO-vs-analogue, there is no impedance mismatch, and £25 analysers could have been used (but weren't since the £350 SA was easier to use)

By all means read the article and see whether mechatrommer's points have any validity whatsoever!

3

Beginners / Re: what an oscilloscope recommended for a woman passionate about electronics?

« Last post by Zenith on Today at 11:20:21 pm »

Thanks guys, very kind.
So I don't activate this bandwidth limitation and live in peace. I will let the oscilloscope receive the entire frequency band (200Mhz). Small deviation: while on the Micsig differential probe there is a button to limit the band to 5Mhz, but in this case I believe that for lower signals it is better to activate it, so I have a much cleaner and less noisy signal. Of course if there were peaks every now and then beyond that, I would lose them... 

There is no blanket answer; yes it's great, always use it, or no it's poison, never use it. It's a feature which may be useful, and to use the scope to best effect you have to be aware of these possibilities and their limitations. Experiment with it, so you know what it does, and use it at need, which I suspect will rarely arise.

Tek 475s have a bandwidth filter; 200 MHz, the default, 100MHz, which gives a cleaner display, and 20MHz which gives a very sharp display. It could be useful in certain circumstances. I think most people learn to live with the slight fuzziness of a Tek 475 and regard it as part of the charm of the instrument.

4

EEVblog Specific / Re: EEVblog 1612 - Siglent SDS1000X HD 12 bit Oscilloscope Teardown

« Last post by Geoff-AU on Today at 11:07:06 pm »

That would mean they have some unfortunate bottleneck in the screen image rendering path.

Cost cutting, the Zynq in the 1000HD does “everything” while the 2000HD has 3 or 4 chips with FPGA fabric including one which is a dedicated display chip.. and an (older) Zynq.

Some subtle differences in functionality, 1000HD has hardware mask testing, 2000HD has hardware mask, averaging, and ERES. 

I noticed the slow screen updates in the side by side right away, that kind of thing bothers me more than it should. Love a fast UI.

5

Repair / Re: IWATSU oscilloscope Cal signal square wave showing as ramped / curved signal

« Last post by BrokenYugo on Today at 11:05:44 pm »

Likely no issue, just more setup work to do.



I've seen some that have the adjust screw on the BNC end, but the basic procedure holds for more or less every scope built since the 70s.

6

RF, Microwave, Ham Radio / Re: Cascade RF Frontend 2.4GHz possible?

« Last post by vk4ffab on Today at 11:03:15 pm »

@vk4ffab


I only want to know, if such an IC can directly drive such an IC or if passives are absolutely required. That is all I asked for. Let the gain be my problem.

Single-ended 50 Ω input and output ports.

^^ from the datasheet, 50ohm in, 50ohm out, I could check that there is no dc on either the in and out ports, if there is it would require a blocking cap, other than that, as long as the in and out ports do not see more power than they can handle and you can sequence the switching from tx to rx accurately enough so they both have fully switched before going into TX, because you do not want the switches being hit with highish power rf while switching, then sure, I cannot see a reason why it cannot work, other than you now have 2 LNA blocks in series on receive and its impossible to say what that would do to receiver performance. The receiver getting overloaded could be very detrimental to its performance.

So they answer is Yes, No and Maybe? In TX I would say yes, on RX I would lead towards no because the 2nd lna is likely to distort when the first LNA has a strong signal and maybe the receiver can deal with strong distortion, but probably cannot. You can always just do what most hams do and just give it a go and see what happens, but, what you really need is a gain block with switches before your IC that does not have an LNA on rx. I do not know if such a thing exists.

7

Test Equipment / Re: Choosing between entry-level 12-bit DSOs

« Last post by Mechatrommer on Today at 10:57:24 pm »

looking for "credential", i found an example how BW limited scope can miss things out... you can quick read the possibly fabricated story until the Analog Discovery "recommended for beginners" screen capture... how it missed 96MHz oscillation... the fix? (or verification) use SA (probably an expensive one) and a 300MHz scope... so the conclusion? if you want to see oscillation or something wrong in your circuit, get a SA and 3x the suspected oscillation freq DSO... so for example... if oscillation is at 300MHz, get a 1GHz DSO (and SA too and other TEs mumbo jumbo) one, so your measurement is metrologically sound... thats the (spending) more, for less (novel or fancy technique work) just as we typically did or recommended Practical Traps with a One Transistor Audio Amplifier, Solderless Breadboards, and Oscilloscopes unless your name is Jim William, your tin can novel technique will be commonly accepted as crap by professionals (or retired there is)... ymmv.



 

 

what could possibly go wrong with emitter follower on breadboard unless purposely impedance mismatch at long input lead, no?

8

Projects, Designs, and Technical Stuff / Re: Using a current output DAC to control laser diode brightness: which IC to use?

« Last post by bson on Today at 10:55:30 pm »

1. I need to EITHER modulate the BRIGHTNESS of a laser diode from zero (no light) to an arbitrary brightness (not sure what that is yet)
OR I need to modulate the FREQUENCY of a laser diode (OR modulate the emitted light) between either 525–550nm or between 375–400nm (whichever is easier/cheaper)

You can also modulate the duty cycle rather than the period frequency, which tends to be simpler.

But still, why a period of 1MHz?  You can more easily pulse it at a few kHz and vary the duty. Or even lower frequency - usually when dealing with LEDs a few kHz is more than sufficient to avoid visual flickering and strobe effects, but it's not like this should matter with a laser.

9

Repair / Re: IWATSU oscilloscope Cal signal square wave showing as ramped / curved signal

« Last post by BlownUpCapacitor on Today at 10:55:01 pm »

under compensated probe

10

Test Equipment / Re: Choosing between entry-level 12-bit DSOs

« Last post by wasedadoc on Today at 10:50:54 pm »

And again, sin x / x reconstruction is rather crude so that doesn't help.

Why do you keep writing that?

Because it is. As I wrote before you can use much longer filters which result in much better curve fitting so you can reconstruct frequency content very close to Nyquist. The computational power you have available is the limit.

How can you have much longer filters than the infinitely long sin(x)/x ?  A modified version can be as long as you want within the available computational power.  Give us the details of one of your filters and show that it is better than can be achieved with the well-known 'windowed' versions of sin(x)/x allowed the same computational power as yours.