Recent Posts

1

Beginners / Re: buying a oscilloscoop

« Last post by tggzzz on Today at 01:06:23 pm »

Indeed this is good advice. One suggestion that I can give regarding the choice of oscilloscope that mitigates this issue is a fully portable unit, which is isolated from anything else. I have one of these newer portable oscilloscopes from Zoyi/Zotek (ZT-702S) that allows troubleshooting several minor issues common in computers such as power supply ripple, RTC clocks, activivity on data or control lines, monitor reset lines, etc. Naturally, you might find yourself wanting for a better unit later in time, but these units are a great starter.

Before all the traditional scope-floating hell breaks loose, it should be mentioned that while these portable (aka floating) scopes are good for preventing the damage of the scope and DUT (as long as all ground leads are connected to the same potential), they do not inherently make measurements safer for the user. That part should be understood, and it was a good advice to accumulate some experience and knowledge before proceeding to probing higher voltage circuits.

Actually they might make it marginally safer. Avoids deafening/blinding/lung damage/heart attack when something blows up and/or catches fire
Apart from those minor considerations, you are right: an isolated scope woudn't make it safer.

HV differential probe are, for many use-cases, the appropriate choice of probe.

The OP might like to consider that they will probably end up spending money on a scope plus X, and hence to leave budget available for X.

2

General Technical Chat / Re: Do you think an LED is a resistor?

« Last post by Sredni on Today at 01:06:13 pm »

non linear system has linear approximation around a small operating point....

STOP THE PRESSES!

... oh wait, that's the underlying principle of how spice AC analysis works.

Small signal analysis has nothing to do with what we are discussing here.
The resistance I talk about is the static resistance, not the dynamic or incremental resistance of small signal analysis.

Try again.

That was your long winded and dithering proof:

So, we are now seeing the diode as a voltage dependent resistor. Let's see... what is the resistance 400mV? Let's zoom in:

[MASSIVE IMAGE]

I'd say it's about 23.2 kohm.
Let's see what is the resistance at, I don't know, 660 mV (about 5mA of diode current). We can compute it by hand of course, but on the graph we see it is 132 ohm.

[MASSIVE IMAGE]

Now, let's see if we can make something with these values...
[snipping conversational fluff]
Ok, exact same results, if we neglect a bit of rounding error in reading and setting the values.
Now, take your black boxes out of the fridge. Put the diodes D1 and D2, and the resistors R1 and R2 inside a black box each. Shuffle them around. And tell me: without looking inside the black boxes and without resorting to second order effects (like temperature dependence, or changing the other circuital parameters to change the operating points) can you tell me which are the diodes and which are the resistors, by simply measuring voltages, currents and powers?

So to try and claim you're not relying on the well known small signal AC parameters is plainly incorrect.

If you dont like relying on small signal characteristics, perhaps "try again" with your explanation/justification.

Again, small signal analysis has nothing to do with anything I have written in that post.
Nothing.
I zoomed in on the V-R characteristic to find an accurate value of the static resistance. Not the dynamic, or incremental, or small signal resistance.
Then I used the static resistance at a chosen voltage or current to choose the limiting resistor that would have set the chosen operating point.
Then I showed that using a resistor with the correct static resistance value would give the same variables in the circuit..
If you want to waste a bit of time you can create in LTspice a voltage controlled resistor that has the same R=R(V) dependence of a 1N4148. You will then see that it will behave (secondary effects apart) as a diode, confirming that it's the variable resistance. that gives a diode its behavior.

Go ahead and try.

3

DIPtrace / DipTrace 5.0 Beta

« Last post by SergElectron on Today at 01:05:35 pm »

"Plugins, PCB Calculator, Planar Inductors, Digital SPICE Simulator, Via Stitching, Via Shielding, Export to PDF, Updating PCB from Netlist, etc..."  are waiting for you in DipTrace 5.0 Beta.
All features overview is here:
DipTrace 5.0 Beta is ready for testing! Your feedback will be greatly appreciated.
Download it now: https://diptrace.com/download/download-diptrace/

4

General Technical Chat / Re: Do you think an LED is a resistor?

« Last post by armandine2 on Today at 12:56:03 pm »

I might start a new thread because this is so interesting -

Do you think a Vise-Grip is a hammer?

After all, I can hammer a nail with a vise-grip. If I give you two pieces of wood with driven nails - can you tell which one had the nails driven with a hammer and which one has nails driven with a vise-grip?

So I want to know if a vise-grip is in fact just another form of a hammer. Prove me wrong.

I was also thinking on mechanical lines 

... so if the electrical terms Resistance, Inductance and Capacitance have their mechanical equivalents what is the OPs mechanical device analogous to the LED? 

5

Beginners / Re: Comparator problem

« Last post by elki on Today at 12:51:45 pm »

Further investigations revealed that indeed the voltage goes above 3V on the input pin of the comparator, however, the initial pulse is below 1.5V. Looks like comparator drives it to the rail. Adding a 1k resistor to the supply rail fixes the problem at the cost of reducing the comparator output to about 1V. Not ideal.

6

Repair / Re: Rohde Schwarz CMU200

« Last post by ON4GN on Today at 12:43:44 pm »

I checked the voltages again and they are all normal.
But I tested without the CMU-B68 and I can use the CMU200 as a spectrum analyser and the RF generator is OK.
That is actualy all I need.

7

Beginners / Re: Arduino Nano V3 and LCD 128x64 how to connect them

« Last post by themadhippy on Today at 12:43:43 pm »

Soldering isn't hard.

indeed its not,however adding headers to a nano aint really an ideal starting point,might want to  get a bit of 0.1" stripboard and some extra headers and get your technique dialed in first.

8

Repair / Re: HP54600B with spike problem with and without signal

« Last post by T3sl4co1l on Today at 12:39:35 pm »

I'm guessing it's 2V/div, 5V supply, and the ramps are open bus (with weak pull-ups, but nothing reading during so it doesn't matter).  But this would be a good place to have multiple channels showing the strobe signals.

Another tweak that may be diagnostic: loading the signal (particularly the suspicious pin) with a resistor of say 1k, down to even a couple hundred ohms, pulling to VDD or GND, or with a capacitor of some 10s of pF, and see how much is necessary to cause data corruption.  Most likely, all the other signals will be well-behaved (tolerant down to, say, 200 ohm or so, or up to 30pF or more), and the suspect signal fails with much less (or in the pull-up case, potentially improves).  You will see the effect of these loads on the scope trace.

Tim

9

Beginners / Re: Comparator problem

« Last post by elki on Today at 12:37:24 pm »

The maximum voltage on the input pin does not exceed 1.5V. The issue might be elsewhere. Any other suggestions on how to protect the input signal are welcome.

> however, the same effect of the input signal getting distorted as in the 'biased' version.

Check the voltage on comparator input pin. It should not exceed 3.0V

10

Other Equipment & Products / Re: Dymo 550 Thermal Printer DRM Hacking

« Last post by RethoricalCheese on Today at 12:35:30 pm »

Tested all 12 of em. All of them are still in memory.

Btw, there are 2 typos in slix2_tag_emu 11. Missing a couple commas. Not that it matters to this case.