Recent Posts

1

Projects, Designs, and Technical Stuff / Re: Reactive Source Resonant Transformer

« Last post by Benta on Today at 09:55:16 pm »

Well..,
"This design posses (sic!) the potential to"... do something. Perhaps provide a therapy for AntiVaxxers? Or QAnon followers?

I dunno.

2

FPGA / Re: Analog video output with FPGA ?

« Last post by Jaunedeau on Today at 09:55:06 pm »

Since you mentioned using MCUs (I think?), note that generating RGB video at these resolutions would be plenty feasible with just a RP2040 and its PIO. But given its limited number of GPIOs, you'd probably have to limit the bit depth to something lower.

The PIO is plenty of fun and I'll try playing with PDM on the PIO, but with max overclocking and 4 bit depth per component, I would get only 3 samples per pixel with pwm and 160 px per line... still a bit low for my all grey / alternating black and white pixels problem. I even thought of a dual rp2040 solution with one acting as an SPI ADC, but the stm32g4 (170MHz, requires no external flash, $2.5 for one piece in 64pins package / 52 gpios and has an real datasheet ^^) seems a simpler solution if an R2R ladder + calibration can do the job.

3

Test Equipment / Re: SDS800X HD Wanted Features

« Last post by tautech on Today at 09:54:12 pm »

How about making the tabs a tiny bit smaller too?

Not possible without sacrificing space needed for indication of channel settings.
BW limit, Hidden (but active) etc.

4

Beginners / Re: LiPo battery charging problem

« Last post by amyk on Today at 09:53:26 pm »

I assume this is a 3s pack? Yes, there are lion cells which are rated at 4.4v full:

https://electronics.stackexchange.com/questions/519625/4-4v-li-ion-polymer-battery

The disadvantage of charging them to less than 4.4v is lower capacity, but the advantage is they'll last longer.

5

Projects, Designs, and Technical Stuff / Re: Drive 36" long pcb traces

« Last post by davethomaspilot on Today at 09:52:08 pm »

Found a couple of useful "nuggets".

Typical propagation delay of a signal with FR4 substrate is 6 inches per nanosecond.

The empirical data found in the test is that when the signal delay on the pcb trace is higher than 20% of the rising edge of the signal, the signal will produce significant ringing.

So, one approach would be to add a series resistor at the source to slow the rise and fall times so they are slower than 5x the signal propagation delay.  If the resulting tr/tf is too slow, break the long trace into segments driven by separate buffers.

36" is 6 nanoseconds prop delay by the above guideline.  So, Tr/Tf would need to be longer than 30 nanoseconds.

That seems reasonable for 2 Mhz--60 nanoseconds for Tr/Tf and (500-60)/2  = 220 nsec for the up and down times of the the clock signal).

So, I can pick resistor value based on what I actually see once I get pcbs back.

Comments?

6

Test Equipment / Re: SDS800X HD Wanted Features

« Last post by eTobey on Today at 09:48:08 pm »

Any advanced user with some active Math channels.

A few more words would have been useful, and would have sounded much nicer...

From 8+ tabs there is a point that would make those buttons actually better than scrolling IMHO. But then i would say drop that timestamp (make it floating or whatever) and make those buttons slightly bigger, and have the fifth element beeing covered less.

How about making the tabs a tiny bit smaller too? There is some room in the middle.

7

Test Equipment / Re: Equipment Discounts from Saelig

« Last post by awakephd on Today at 09:44:28 pm »

I am about ready to pull the trigger on a scope. Could I also get the discount code? Thanks!

8

Projects, Designs, and Technical Stuff / Re: Accurate sine wave in terms of amplitude

« Last post by tggzzz on Today at 09:43:21 pm »

>Depending on your (apparently secret) requirements...

Or I simply don't know yet. Pretty much all the requirements (=the rest of the circuit) depend on what kind of signal I can generate. The frequency can be between 1-10kHz. Amplitude can be between 200mV and 5V. I don't know how much THD (or any other parameter) affects to the device. I need to finish the design, build the device and test. And then probably, re-design the circuit, build another device and test again. Maybe at this point I actually know all the key parameters, including if THD matters or not.

But I do know today that I am iterating options how to generate sine wave - as clarified in the initial message including an example circuit.

Quadrature oscillator might be "the fresh idea I was looking for". Just that none of the first examples I tried to simulate on LTspice didn't work. Like this one:
(Attachment Link)

Probably a simulation related issue - I need to analyze it further...

sw guy

Now why couldn't you have simply said that earlier? A lot of time would have been saved.

Your first task is system modelling, to calculate what should work.
Your second task is system design and simulation, to determine allowable tolerances.
Your third task is detailed design, simulation, to verify you can implement the system.
Your fourth task is to build and test.

You are asking us about task 3, without having done tasks 1 and 2. That is bound to fail, slowly and messily.

You are doing the equivalent of jumping straight into coding, without having requirements nor architecture. See the problem?

Once you have a successful system simulation, e.g. using a spice sine wave voltage source, you can build a lab prototype using an off the shelf function generator. Only after the lab prototype is.working does it become worth considering  implementing your own generator.

9

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

« Last post by awakephd on Today at 09:43:10 pm »

Well, I had planned to drop out of this discussion, in part because I still had a month to go before I would have funds in hand to make a purchase ... but unexpectedly the funds have arrived early, so now the pressure is on to make a choice ... so I am back to seeing if I have fully understood the pros and cons of each, choosing between the Siglent SDS804X HD and the Rigol DHO804.

There are many things that seem to point to the Siglent SDS804X HD as the obvious choice (2G sample rate; better math functions; more USB ports; fewer bugs?). However, to the extent that I have been able to follow the discussion above, at least some of the advantage of the Siglent seem to be tied to more advanced topics than I expect ever to get into. (Yes? No?)

Meanwhile, there are some features that the Rigol brings to the table that I find attractive, including the slimmer size, possibility of powering from a battery pack, HDMI output, easy addition of wifi capability. VESA mount might also be valuable for my limited workspace.

I am getting ready to read back through the extended threads that detail performance, bugs, desired features, etc. for each of the units, but in the meantime, I have three specific questions:

The last feature I noted for the Rigol leads to the first specific question for this post: Have I understood correctly that there is no way to add wireless to the Siglent other than through the ethernet port?

Second specific question: I seem to recall reading something that suggested that the probes that come with the Rigol 804 are better (? or have a higher BW rating?) than those provided with the Siglent. Is that true, and should I care?

Third specific question: I think I would likely want to "hack" either of these units up to 100MHz and greater memory depth. From what I am seeing, this seems to be easier for the Rigol than for the Siglent - true? (This also connects to the previous question - if I want to hack up to 100Mhz, are the probes going to make that less successful with one vs. the other?)

10

RF, Microwave, Ham Radio / fake MPF102s from AliExpress

« Last post by graybeard on Today at 09:41:59 pm »

I ordered some MPF102 n channel RF JFETs from two different vendors on AliExpress since domestic versions are no longer available.
What I got were remarked NPN BJTs, not JFETs.  See the attached images.