Recent Posts

1

Metrology / Re: ADR1399 reference

« Last post by Andreas on Today at 03:39:40 pm »

Hello,

update on my ADR1399 ageing reference board after having added 100uF to the output of the LDO voltage regulator on day 246.
(HEF4052 multiplexer has been used since day 190 / previously it was a MAX4052A)

Now I have a much lower standard devation especially on the metal can packages (from 0.25-0.3 ppm to 0.1 - 0.15 ppm)
But also the LS8-packages went down from 0.15-0.3 ppm to 0.1 - 0.17 ppm

And again the output voltage shifted. So I fear that I will have to repeat the ageing drift measurements with a new set of references.

With best regards

Andreas

2

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

« Last post by NNNI on Today at 03:31:08 pm »

I finally took the time to read through all of the messages posted and process them properly.

I think I finally see some merit in removing as much charge from the integrator as the clock resolution will allow. As per the Landsberg rundown scheme, if I use the same clock to carry out rundown as I use for runup, the rundown counts can basically just be added to the runup counts. This eliminates the need for more constants that would need to be calibrated somehow. The effects of comparator hysteresis can be removed to a large extent by using some kind of zero-crossing slope amplifier, similar to the one described by Jim Williams in National Semiconductor App Note 260. This way, we don't need to add a certain amount of clock cycles' worth of charge into the integrator to compensate for comparator hysteresis. The board I designed has a footprint for such a slope amplifier, but I removed it since it had some issues. I will have to experiment with it some more. The residue ADC will have to digitize a much smaller integration range, I guess calculating that range mathematically and figuring out gain such that the small amount of charge left in the integrator spans the residue ADC's range will be most beneficial.

Of course, the latter part depends on the integrator starting and ending within that specific limited range. Dithering might necessitate a larger voltage range on the residue ADC. I will have to play around with my board to see what kind of numbers I get.

Regarding jitter, the numbers from a crude test performed by a friend indicate around 50ps RMS jitter, measured between successive rising edges of a GPIO toggling at 20MHz (done using PIO) with a 400MHz overclock. I am not sure how much of this comes from the crystal and how much from the PLL, and if a better crystal will make a difference. More (proper!) measurements will have to be made.

3

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

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

Generating a precise & stable amplitude (and frequency) square-wave isn't difficult, see below.
However extracting a precise & stable sine-wave from this square-wave may be more difficult than expected.

Fully agree and I am aware of that. Since the frequency is fixed as well as the amplitude, that might be doable well enough. I have to do some testing and thank you for everyone about ideas and considerations.

What could be a proved single opamp for a wien oscillator?

4

Beginners / Re: What function generator, that does a bit more than just a simple signal

« Last post by shapirus on Today at 03:21:07 pm »

JDS2800 can't do AM/FM btw, so look elsewhere if you need that.

PWM single pulse deviations, not via its standard means, either.

Introducing spikes, probably yes, by creating a respective wave on second channel and then combining them externally.

Or maybe it's possible using arbitrary waveform, but I've never tried that.

5

Test Equipment / Re: TinySA Ultra launched

« Last post by shapirus on Today at 03:16:09 pm »

More like a cosmetic issue, having all those random waveforms displayed between steps, especially since it's not the primary function of this device.

It would be nice if it could be fixed without compromising other functionality, but otherwise no big deal.

6

Beginners / Re: LC filtering for combined Vref/VDD of ADC

« Last post by temperance on Today at 03:14:55 pm »

Bonus: LDO at least gives [the chance for a] more accurate supply/ref, potentially reducing calibration error.

My posts suggests the use of a shunt reference instead of an LDO which is a better option if power loss is not an issue. It doesn't suffer from reduced PSSR when operating close to Vin like the LDO.

7

Computers / Format a 256GB pendrive with FAT32 using a windows 10 pc

« Last post by Karel on Today at 03:14:27 pm »

A friend bought a new usb pendrive with a capacity of 256GB.
It worked fine with his windows 10 pc but his DVB-T decoder with usb slot (used to record tv-programs)
did not recognize the pendrive.
Apparently the decoder accepts only pendrives formatted with FAT32 but our pendrive was formatted with exFAT,
so we used windows 10 to format the pendrive with FAT32.

Then we discovered that windows refuses to format a pendrive with FAT32 when the volume is more than 32GB 

I took his pendrive home and used my Linux machine to format the pendrive with FAT32. Problem solved.

Morale:

Linux is a system of possibilities.
Windows is a system of limitations.

8

Repair / Help needed identifying a Zener/TVS Diode (Toyota ECU)

« Last post by Signal Simon on Today at 03:11:18 pm »

I'm attempting to repair a Toyota engine ECU that it seems has had an over-voltage event, possibly failed alternator or loose battery terminal.
I have found two failed diodes, D401 and D402 (Shorted) marked "1E 8D" which just seem like series diodes from the main power supplies, so have fitted 1N4002s in their place.
However my mystery is D404.
From the screen print, it's a Zener and is directly across the internal supply.
One of its circuit tracks has blown open, so there was obviously more than just a bit of a transient.

The diode is marked: T S5225 8.C

The T I'm assuming signifies Toshiba.
It's in a substantial case 10mm diameter and 4mm thick, similar to a Motorola MR751 series.
Can't find any reference online, it obviously isn't a 1N5225

Logic says the Zener(TVS?) voltage should be in the region of 18 to 24Volts

Any help appreciated

Thanks,
Simon.

9

Test Equipment / Re: Siglent SSA 3021X... Ooops

« Last post by Joel_l on Today at 03:10:33 pm »

Something very strange happened.

It occurred to me that I do have a better way to check the input impedance of my SA, I can use my antenna analyzer ( at least for a limited range ).

I hooked it up and did a sweep around 20MHz, it showed me an SWR off the scale. I wanted to see what the impedance looked like so I switched it to do a Smith chart. When I did the sweep, the SA barked at me with an overload. I went and changed the attenuation did a few more sweeps and things looked good. Went back to do a SWR sweep and it looked good 1.2:1.

I disconnected the antenna analyzer and hooked my TX back up and it worked just fine, no more high SWR warning.

I need to look at this more and make sure I'm not chasing bad data.

10

Repair / Re: Precision Standards AC-DC Differential Voltmeter 360A - manual

« Last post by calin on Today at 03:09:26 pm »

Does look like working / turning on somewhat without releasing any magic smoke. But that's about it, the dial indicator just sticks to the max when I try to measure anything  and that is it.
I am a tad weary sticking my fingers too much in, when this thing is running, as it does produces internally some high tensions especially on the higher ranges.
At worst I can gather some really nice precision resistors from the innards and end up with a nice project box if nothing better comes out of it