Recent Posts

1

Microcontrollers / Re: primitive serial CLI / Console for embedded systems - Ideas for implementation?

« Last post by tooki on Today at 04:00:00 pm »

https://interrupt.memfault.com/blog/firmware-shell

That is the code I started from to develop the CLI for a piece of lab equipment I built.

The use case is practically identical to yours: human use for development, but ultimately controlled by Python scripting for experiment automation.

In my case (a 6-channel capacitance meter built around Smartec’s UTI chip, with a PIC microcontroller to read the UTI’s weird period-modulated output and communicate over RS-422), I made some settings “modes” (verbose on/off, debug on/off, echo on/off, and fast/slow mode) that persist between measurements, while others are per-call, like the channel and number of measurements.

For example, “read 1 20” takes 20 sequential readings of channel 1 and returns them as a list, while “avg 1 20” takes 20 sequential readings of channel 1 and returns a single averaged value. In debug mode, the result includes statistics. Verbose mode outputs the units (pF), extra human-friendly info, and line numbers on lists. The idea is that in automated operation, echo, debug, and verbose are off and the unit returns bare numbers that are easy to parse.

I also added single-letter “aliases” of the commands, so that the two examples above can be typed as “r 1 20” and “a 1 20”, respectively.

The mode commands accept a Boolean value (true/false, t/f, 1/0, and on/off are all accepted), but function as a toggle if no value is passed. This allows the control script to positivity set a known configuration before sending commands. One of the things the CLI parser returns is the number of arguments received (including the command itself), so you can easily make your command handler do different things depending on the number of arguments.

Oh yeah, and I added backspace support (quite handy for us humans).

2

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

« Last post by Kleinstein on Today at 03:57:39 pm »

I would not go for just a crystal, as the frequency can be effected by the µC and this can cause nasty INL problems.
There are relatively cheap boxed oscillators that can do the job (some 1 ps jitter specs seem to common).
The question is if one needs external latches / flip flops for an extra sync. step. The extra external sync step may reduce the jitter a little and reduce possible delay modulations at the µC, but it also adds power consumption and possibly EMI problems. There is a good chance that one could skip it.
With an external sync one would likely use a relatively low clock (like 12 MHz), which should make the USB use easy.
Without an external sync one may opt for a faster clock (maybe 48 MHz if one wants USB while the ADC is active).
For the processing power already 12 MHz should be sufficient. A DMM would anyway have a 2nd µC at the output / interface side.

3

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

« Last post by Antonio90 on Today at 03:57:22 pm »

comical or not, professional or not, sds800x cannot see 400-500MHz even on one channel active, prove me wrong.

🤣🤣🤣 I don't need to. The FACT of REALITY is that if you're trying to measure outside of the scopes designed bandwidth, then the results simply won't be accepted by any professional. The results shapirus showed of his DHO800 measuring 500MHz were TERRIBLE. If you think that's something to be proud about, I don't know what to tell you.

Do you need to measure a 500MHz signal? Your scope better be CERTIFIED to do so, or you could be subject to legal action when the product you're trying to sell doesn't meet specs, or the device you certified as functional isn't. Standards and reality matter, unless you're talking about a toy.

Are you looking for a toy or a tool?

Your scope will not be "certified" whatever that means when out of cal either, and I bet most, if not all of your equipment is not calibrated regularly.
Certainly mine isn't, and I intend that to stay that way.

I couldn't care less about 500MHz signals right now, which doesn't mean being able to visualize that signal is completely useless for everybody. Very few people buy either of the scopes discussed in this thread for certification and measurements in which legal liability is involved, and nobody without periodic calibration.

Let's keep the discussion where it belongs. I do agree that the SDS800X-HD is a better oscilloscope overall. I can also see why, for basic use, the DHO800 can be more than enough and in that case in particular it might be a better purchase due to some usability and convenience advantages.

That being said, I just got my SDS800X-HD. I'm thinking of buying a DHO800 just to compare them thoroughly, but it's a bit of an expensive thought.

4

Projects, Designs, and Technical Stuff / Re: Build or buy? Multi-level vessel temperature logger

« Last post by paulca on Today at 03:56:15 pm »

Yea, then it only has a "Request a quote" button, it's too expensive.

Interesting.  So for the DIY approach, a silicon or stainless tube. 

8mm ID (which I have) will just about take a TO-92, so it will take DB8120b 'one wire' senors, requiring only a pair of wires for the whole "bus" of sensors.

I can probably very easily layout the apparatus without any PCB needed.  "Pull it through" the pipe/tube and then, gravity fill the tube with epoxy.

The only bit that sounds like it will go wrong is the last part.  I don't have any thing resembling a vacuum to pull the expoxy (or silicon sealer) through.  Not unless I get really runny, designed for the purpose epoxy.

EDIT:  I also need to make sure the epoxy (and everything) is okay at 105C.

5

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

« Last post by nctnico on Today at 03:54:45 pm »

The original Signal can be reconstructed with much wider filters but they'll only work if the signal is perfectly periodic.
I was wondering what happens if the signal isn't periodic. It could go very wrong.

No, it does not have to be periodic. "Perfect reconstruction" only requires that the original signal sampled by the ADC sampled was bandwidth-limited.

And with a realizable real-world reconstruction/interpolation filter, this bandwidth limit is not 0.5*sample_rate, but lower. For the Rigol, it seems to be about 0.3*sample_rate.

Agreed. In addition I'd like to add that sin x / x reconstruction (which is a relatively simple filter to implement) can reconstruct little over  fs / 2.5  (0.4 * fs). Anything less I consider broken. I have come across a few DSOs which had trouble doing sin x /x reconstruction at fs / 2.5 but their manufacturers fixed the firmware quickly. Bottom line: consider the current Rigol reconstruction as broken and needs fixing.

6

Other Equipment & Products / Re: Lets see your Nixie Tube equipment

« Last post by tggzzz on Today at 03:54:29 pm »

One of my HP 740B DC Voltage Standard/Differential Voltmeters.  On its side for troubleshooting.  The Nixie tubes display the knob positions, they don't dynamically change with input voltage.  So just an electronic version of the mechanical digit wheels on a Fluke differential voltmeter.

How ... naff!

The only reason I can think of for that is marketing run wild - possibly due to an (ignorant?) large customer wanting it.

7

Buy/Sell/Wanted / WTB (US/NA) Battery and Charger for Flir Ext (compatible with E4, E5, E6, E8)

« Last post by ZGoode on Today at 03:54:29 pm »

I'm looking to buy one battery and one charger for the Flir Ext family to replace charging over micro-USB.  If anyone has any extras, especially of the charger, I would be happy to buy one off you.

8

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

« Last post by mawyatt on Today at 03:52:54 pm »

On paper, sure, but my question is how much of that translates into an advantage in practice.

That's the point we don't "practice", we performed in real time, no backups, or woops, or awe sh*its, missed that, our career and reputation were/are on the line in everything we did/do.

Today things are a little less stressful as we are semi-retired, but still adhere to the "no excuses" policy wrt to electronics design, and the Siglent is simply our more Pro Level instrument IMO.

Please remember we have both Rigol & Siglent, and don't need to defend nor exaggerate the performance of either

Of course YMMV

Best,

9

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

« Last post by wasedadoc on Today at 03:51:28 pm »

No, it does not have to be periodic. "Perfect reconstruction" only requires that the original signal sampled by the ADC sampled was bandwidth-limited.

Nope.

The signal in this image is bandwidth limited (5Hz signal, 11Hz sample rate) but sin(x)/x won't reconstruct it unless the filter is infinitely wide and the signal is periodic (which can't happen in practice).

That signal has components above 5.5 Hz.

10

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

« Last post by KungFuJosh on Today at 03:48:44 pm »

comical or not, professional or not, sds800x cannot see 400-500MHz even on one channel active, prove me wrong.

🤣🤣🤣 I don't need to. The FACT of REALITY is that if you're trying to measure outside of the scopes designed bandwidth, then the results simply won't be accepted by any professional. The results shapirus showed of his DHO800 measuring 500MHz were TERRIBLE. If you think that's something to be proud about, I don't know what to tell you.

Do you need to measure a 500MHz signal? Your scope better be CERTIFIED to do so, or you could be subject to legal action when the product you're trying to sell doesn't meet specs, or the device you certified as functional isn't. Standards and reality matter, unless you're talking about a toy.

Are you looking for a toy or a tool?