Recent Posts

21

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?)

22

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.

23

Test Equipment / Re: Cheap oscilloscope for checking mains power quality? Also logging equipment.

« Last post by adam4521 on Today at 09:41:23 pm »

For low cost power quality logging I've had some success using a commercial-grade electricity meter: Schneider PM5110/PM5111 for example which you can easily find used/surplus. Install into an adaptable box. Lower cost than a power quality analyser, and you can read out voltage, current and harmonic data to a computer via Modbus RS485 interface. But this will be a bit of a do-it-yourself project.

For RCBO/GFCI nuisance tripping, often this will be linked to a switching transition -- something being connected to the system or switched on, that creates a transient unbalanced current in the live and neutral conductors. For LED flicker, it's traditionally associated with unstable timing of 'phase cut' dimming: the lighting driver is interacting with the dimmer. If you really want to see what is going on you will want the oscilloscope, but you will need to convert the current signal you want to observe to a voltage signal. As electrician, you would be confident making up a circuit breakout box with a CT and suitable burden resistor inside? You might make a specific one for measuring residual current -- look for a 'zero sequence CT', which has higher sensitivity.

Multiple times on the forum we discuss safe connection of oscilloscope to mains. The current transformer appropriately terminated will be ok. Differential voltage probes are great (but relatively expensive, unless you land one second-hand). You can use a voltage transformer to keep voltage measurement simple, but won't be super-accurate for observing some of the transient events. Battery powered oscilloscopes from Fluke are purpose-made, but they are really expensive, even for really old ones.

24

Other Equipment & Products / Re: Three most useful tools I got from AliExpress

« Last post by watchmaker on Today at 09:40:16 pm »

Links to the tools please. 

The board holder does look very nice, and do I see you invested in a chip tester? The one Adrian Black (digital basement) used to test al kinds of chips with?

I really like the board holder.    If a board is too long, you can always hold it sideways or buy an Aluminum bar at a metals supplier.

Yes, I am assembling the retrochip tester from 8bit-museum.de.  I found it is much cheaper (but more painful) to order the parts from DigiKey; $120 vs about $250.

Per Request:

https://www.aliexpress.us/item/3256806317632603.html

https://www.aliexpress.us/item/2255800993178532.html

I have to find the ProsKit desolder gun.  But it was about $100; bought it as a "first timer" on another account.  (Yes, I am that cheap!)

25

General Technical Chat / Re: Russia and China to Build a Nuclear Plant on the Moon.

« Last post by tatel on Today at 09:39:59 pm »

It is certainly doable. My previous comment wasn't an endorsement of western safety standards.  In the west we are trending towards finding that a one in a million chance of someone getting a hangnail is unacceptable.  People in the US are currently going crazy over a vacuum thermos that has a lead seal that is not externally accessible, and claiming a billion dollars of emotional damage from being in the airplane that lost a window.

Yeah, after Fukushima all that hype about western secure designs is now clearly understood as BS, one only needs just a functional brain. But, hey, we are winning 3 to 1! Not to mention TMI and those "incidents" while developing the thing because then our advantage would be mostly against de Olympic sport ideals...

26

Projects, Designs, and Technical Stuff / Re: (Yet Another) DIY Multislope ADC

« Last post by NNNI on Today at 09:30:40 pm »

I was just about to bring up the point about being able to upload code via USB. It is very convenient and fast. However, programming via the SWD pins (using a Raspberry Pi debugger, for example) is another alternative. I am not sure how much SWD programming is dependent on system clock.

I am honestly not sure when I will be getting back to the project. I left it in a rather messy state, so getting everything running and familiarizing myself with the code diminddl and I worked on nearly a year ago will take some time, plus I have to finish testing my own ideas first. The project files are available, so it should be possible to get your own set of boards for experimentation, or replicate the core circuit (it's quite simple) on a breadboard. I understand your eagerness for the results, but all I ask for is a little patience till I can get everything sorted on my side.

27

General Technical Chat / Re: Cable Management

« Last post by watchmaker on Today at 09:28:50 pm »

 

28

Beginners / Re: Quickly Triggering Sensors - need an oscilloscope? what specs? (AU)

« Last post by nate_syd on Today at 09:22:29 pm »

You need Pattern Generator. https://en.wikipedia.org/wiki/Digital_pattern_generator
https://digilent.com/reference/test-and-measurement/guides/waveforms-pattern-generator
Digilent Analog Discovery 3 -  https://digilent.com/reference/test-and-measurement/analog-discovery-3/start

This was REALLY helpful - much appreciated!
Might grab the Disco2, significantly cheaper & good enough for my use case

29

Microcontrollers / STM32F407 - CMSIS DSP - IFFT not working with audio input/output

« Last post by lukegalea16 on Today at 09:22:20 pm »

I'm currently using the stm32f407g-disc1 and reading an audio input through PMOD I2S2. I've carried out some examples and the hardware is working fine (writing data from the rx to the tx buffer) such as the code below.

Code: [Select]

for (int i=0; i<BUFFER_LENGTH*4; i=i+4) {
txBuf[i] = rxBuf[i];
txBuf[i+1] = rxBuf[i+1];
txBuf[i+2] = 0;
txBuf[i+3] = 0;
}

I now wish to perform the FFT on this incoming buffer, manipulate it (my first aim is to implement a pitch shifting algorithm) and perform the IFFT again. Thus I've tried the following:

Code: [Select]

for (int i=0; i<BUFFER_LENGTH*4; i=i+4) {
fft_in_buf[fft_in_ptr] = (float) ((int) (rxBuf[i]<<16)|rxBuf[i+1]);
fft_in_ptr++;
}

arm_rfft_fast_f32(&fft_handler, fft_in_buf, fft_out_buf, 0);
arm_rfft_fast_f32(&fft_handler, fft_out_buf, fft_in_buf, 1);

fft_in_ptr = 0;

for (int i=0; i<BUFFER_LENGTH*4; i=i+4) {
        txBuf[i] = (fft_in_buf[fft_in_ptr] >> 16) & 0xFF; // MSB
        txBuf[i + 1] = fft_in_buf[fft_in_ptr] & 0xFF;     // LSB
        txBuf[i + 2] = 0;
        txBuf[i + 3] = 0;

        fft_in_ptr++;
}

In the main initialization I'm also carrying out

Code: [Select]

arm_rfft_fast_init_f32(&fft_handler, BUFFER_LENGTH);

My issue is that I get a very very low output (barely audible) with the above code. I might have a scaling issue as I found in similar issues but I still can't get it to work by scaling fft_in_buf[fft_in_ptr].

30

Beginners / Re: LiPo battery charging problem

« Last post by nate_syd on Today at 09:21:12 pm »

If you want to know more about battery longevity - youtube some Jeff Dahn videos, he goes into depth on why you only 80% charge etc.