Okay, I'm getting one! I found these links on eBay:

• OWON PDS5022S, 25MHz, 6K buffer, $369, Chinese.
• OWON PDS6062T, 100MHz, 6K buffer, $649, Chinese.
• Rigol 5102CAE 100Mhz, 4K buffer, $799, Chinese.
• Welec W2022A, 200MHz, 16K buffer, $674, UK/DE.

All of these units have large, colour LCD displays, two 1X/10X probes, and USB-to-PC connections for printing/analysis. These are modern, lightweight, standalone, digital storage scopes.

The OWON models may have an "S" or a "T" suffix on the model number. The "S" indicates a DSTN LCD, whereas a "T" means it has the faster/better TFT style of LCD display.

The Welec model includes free DHL delivery in the purchase price. Some OWON sellers also include free (air mail?) shipping in the purchase price, others want $35 extra.

The Welec is also made in 100Mhz, and 4-channel versions, though I didn't see any of those actually offered for sale anywhere.

I've ordered the Welec W2022A unit for my use here -- 200Mhz (1Gs/sec) should be good enough bandwidth for finding glitches and the like.

Cheers

Shipped it today, so now we'll find out how long DHL Economic shipping takes -- the more expensive express is usually overnight, but this method is reputed to take a week or two.

Oh, and the name Welec is apparently a contraction of Wittig Electronics GmbH, aka. Wittig Technologies, and appears to be owned/operated by three brothers in Germany. It's probably no larger than the empeg team from the early days of the Mk1.

EDIT: Heh.. and the first Wittig product was apparently the pen-style "scope probe" I linked to at the top of this thread, now discontinued.

Cheers

Mmm.. this week's price is $75 less (and cheaper in EU currency as well).

Cheers

It arrived here an hour ago, and I've plugged it in and played with it a bit since then.

• GUI responsiveness is slow to non-existent (EDIT: that's not entirely fair -- see further postings below)
• 1-3 seconds from button press/release to screen responding.
• Works fine as a basic digital oscilloscope.
• The included probes do not have very good clip-tips, nice pins though.
• No documentation on how to adjust 2 of the three adjustments on the probes.
• Oscilloscope features, specifically the FFT/Math functions, differ from descriptions in the Users Guide.
• many some illustrated features appear to be missing.

I hope to establish a dialog with the makers to find out about the missing features, and might end up shipping it back to them for a refund.

Cheers

Well, none of the email links from their web site actually function (mis-configured or out of date), but the email for the original eBay seller (Michael Wittig) works.

He's put me in touch with Thomas Wittig, who appears to be the software techie at least. Like I said at the outset, I think it's just a three man company.



So that's a good sign: they do respond (and quickly) to email.
And they do update their firmware -- most recently just a few weeks ago.

Apart from the missing FFT extensions (useful) and Roll mode (not useful), the rest appears to be as advertised.

And as long as Math and Quick Meas. are both turned off, the scope actually is fairly responsive after all. The manual does warn that turning them on will slow it down.. they just don't say how much.

More as I explore more..

Cheers

I'm having trouble finding high frequency signals to test the 200Mhz end of the scale with.

Here are some screen snaps of the scope showing a column address strobe (CAS) line from a Mk2a. Note that my ground clip was simply on the empeg chassis -- nowhere near the RAM chips.

The screen is much better than it looks in the photographs below, which suffer from some kind of moire interaction with my camera's bayer matrix sensor.

Lovely little "square waves", with a fair amount of ringing:

The screens look nice on that.

When you go in on the timebase, what happens to the trigger position?

I use a Tektronix TDS220 at work which can be utterly infuriating when you change the timebase, it moves the trigger position. Consequently, if the trigger position is off centre, by the time you're down to nanoseconds the bloody cursor is milliseconds "off the screen", and the only way to bring it back on screen is to go back up the timebase and then move the trigger position into the centre before going back to nanoseconds.

Wonder if there's any vids of your scope working? With the "slow" options off, what's the response like?

I could do with a scope at home.

Mmmm.. the software is slightly flakey, which I expected at this price point. Mostly it works rather well.

But with a captured waveform, and acquisitions OFF, one cannot zoom the waveform vertically. Horizontal zoom works, but not vertical zoom.

Also, when horizontal zoom is set at 50, 20, or 10ns/div, the horizontal scrolling no longer functions.

I think both of those are bugs, and I've emailed Thomas about them.

Cheers

Heh.. I really haven't figured that out. The display just seems to jump around with no pattern/algorithm that I can recognize. At the moment, it's useless to me for zooming in on anything other than a repetitive waveform, unless I can capture it again at the higher zoom level.

I've got to read through the documentation again, and figure out what all of the little on-screen indicators represent, and then figure out what's buggy and what isn't.

Cheers

To be honest, the only buttons I ever really touch on the textronix are Timebase, Trigger position and aquisition mode (single, continous). Other than that, I don't really touch any other buttons on it.

The thing that I could really do with is being able to capture waveforms (screenshots) onto the PC, the tektronix can do this but it requires an plug in module which we don't have.

As you say, it's substantially cheaper than anything around it, even if only the basic oscilloscope functions work then it'd probably be a winner for me.

I keep looking at the bitscope year in year out, but everytime I look at it I just think "junk". Even doing "hobby" stuff at home, it'd be severely limiting.

It'll be interesting to hear your thoughts on it after a week or so of working with it.

I actually prefer that (we have a TDS210, 220 and I think a 224). I'm quite used to moving the trigger point to the centre if I want to zoom on it. I just zoom on the centre of the screen rather than the trigger.

I loaded the PC software into VMware (under Linux), to see if it was any good.

Well, it has a fancy GUI to remote-control the scope over USB. The remote control does function, but the remote display in the GUI doesn't work.

The only feature that does seem to work is the Quick Print button on the front of the scope -- it sends a scrollable waveform image to the PC, which can then be saved and/or viewed there.

But the PC cannot zoom the waveform -- horizontal scrolling only.

Here's a saved waveform below. This was saved as a 72KByte JPG, so I opened and resaved it as a 2.6KByte PNG file (without resizing.. they just muffed the JPG, I figure).

The image has no grid lines, so it's not terribly useful. But the Print button in their software can include the grid lines for printouts. Perhaps I should try printing to a file to get them?

The actual image shows Hijack reading the current temperature from the empeg's ds1821 temperature sensor chip over a one-wire bus.

First Hijack pulls the DQ line low for a minimum of 480us, then tristates it again. The chip waits 15-60us, then pulses the line low to indicate presence. Hijack then strobes out the command, 0xAA in this case. The chip then responds with the current temperature reading.

That signal in the most recent dump seems pretty noisy.

Possibly that's due to only grounding to the empeg chassis. Is it still in this case?.

I was still using the chassis for that capture, but just now I did it again, with the ground lead clipped to the chassis screw that is less than 1cm from the trace I was probing. Same result.

Cheers

There are no JPEG artifacts in that image, which would suggest the JPEG "quality" was turned waaay up. JPEG becomes very unoptimal at those levels. JPEG is just a terribly poor choice for high contrast images.

Maybe the empeg is noisy. I would think it is though. Very hard to tell unless you have another CRO nearby to compare with.

Freaky. I've done a lot of 1 wire stuff over the past year, including the ds1821, various battery monitors and the SHA-1 iButtons for secure applications!

The processor I that I generally use (AT91SAM7S256) has the option to enable open drain on every IO pin, which is uber-handy for 1 wire. Just use the normal UART but open drain the TX and tie TX/RX together and you lose all the timing overheard by getting the uart to do it all for you!

Sounds like a handy chip, that. I suppose the SA1100 might be able to do something similar, if it wasn't already using all of the internal UARTs for other purposes!

Cheers

Oh, it is very acceptably quick when running as an ordinary scope, with the measurements and math (FFT) turned off. And even with measurements on, it's not bad. But turn on the math, and it gets slow, and with both on, it gets very slow.

I may put up a short video of it -- I think my tiny digicam can do that, though I don't know what format it makes.

I'm thinking of creating a somewhat detailed review page for this scope, since there's nothing else out there on it yet.

And I've decided to keep it. I do need a scope that's fast enough for digital work. Even with all of the current flaws, there's nothing else out there, at double the price, that can do 200Mhz better than this one.

Right now, it's a great regular oscilloscope, with the crucial added capability of freezing the display (and saving/printing it). As a storage scope it has issues: scrolling / zooming within the frozen display works some of the time, not others. The Wittigs have this to say about the scroll/zoom quirkiness:

We have been informed already that these have to be repaired in the next version ... I have forwarded this mail to the developers. Will inform you when the firmware release become available soon.

So it might get fixed, or at least made more usable. Either of which I would consider a bonus. But even as-is, it's a pretty good scope for the cash.

Cheers!

Oh.. I should also note: two hot pixels on the display, for anyone who is super fussy about such things. I only notice them during the 10-second startup sequence. Yes, it boots up faster than most empegs!

Cheers

It's probably just circuit noise in the empeg. But perhaps you have a fast enough scope to take a similar sample there?

This was just a Mk2a, with latest Hijack, plugged into (60Hz) mains. Test probe on pin-1 of the sensor chip, which is hidden underneath the display ribbon cable.

I'm thinking that we only see the noise because the scope samples at 1 gs/sec. A slow scope might miss most of those glitches. Does that make any sense?

Cheers

The Welec buttons themselves are a very appealing feature of this rig. These are soft, translucent silicone things. The oval shaped ones are backlit by coloured LEDs when active, and they sometimes even change colour: Eg. green/red for running/stopped on the Run/Stop button).

Great visual feedback that way. There are not too many buttons, and they use differing shapes/sizes/colours to facilitate navigation among them.

EDIT: The scroll knobs, on the other hand.. are little clicky rotary encoders, with a fairly low speed limit. Nothing like the scroll wheel on the Tek scopes.

My little digicam seems to record in .avi format. I'm attempting to upload a video to youtube now. It's BIG, though, so this'll take a couple of hours.

Or quite possibly much longer than that.

Here's my YouTube video showing the scope.

Cheers

The CAS line photos from earlier in this thread, didn't show an excess of noise -- just obvious ringing on those. But still.. now you've got me wondering about things.

So I clipped the ground clip onto the probe end, which should result in a rather quiet signal, and still saw noise.

Pretty much identical to the noise background that is present when no probes are connected, shown below. It's about a full vertical div of random noise at the highest vertical resolution, which is 10mV/div for 1:1 probes, or 100mV/div for 10:1 probes.

I don't have another scope to compare with here. Is this worth fretting about? (10mV/div x 10ns/div).

No, this cannot be good. Time to email the Wittigs again.

Hi,

A good test is to direct connect the 1kHz Calibration signal BNC to channel 1 BNC (a BNC to BNC cable) and see what the waveform looks like. You might need to use a coax T and a terminator.

This will give us a better idea of how much noise is present in the input amplifiers and ADC.

Look at several divisions (at least 4) at 1ms rate. look for similar noise on the top and bottom as shown in the picture above. Then go to the fastest speed that allows a rise time to start at the far left graticule and end near the middle (5th) graticule. Check the edge for non-monotonicity (the edge rises and then is stepped or falls, then rises again. There also should not be Overshoot (the ringing you see in your video).

If you see any of these anomolies, you might need to set the input impedance to 50 Ohm. Some scopes will only allow 5 Volt maximum input voltage though, make sure it will handle it. There should be NO waveform anomolies with the 50 Ohm termination.

Clipping the probe ground to the probe tip is a good way to sample the Electromagnetic Environment around a measurement area. You would be surprised what some debug environments look like. It forms a single turn loop probe (similar method as an EMI sniffer probe).

The inductance of the probe ground is really most of overshoot you see in your waveforms (it had better be). The best way to view waveforms is at the receive side and to use a short ground. The smaller the loop area - hence inductance - the more waveform fidelity you will see. If it has a ground ring near the probe tip, get a small spring that fits around the ring and bend one or 2 turns out and shape it for use as a ground for probing. You can see the difference easily by probing activity on the 74LVX74 chip pin 5, 6, 8 or 9 with the probe tip and use the spring ground you made to connect to pin 7. Capture the waveform slow sweep speeds and the fastest that will provide 5 divisions, save it. Then probe using the pin (pin 5, 6, 8, or 9) and use the long ground wire supplied with the probe. You should see all of overshoot go away with the short spring ground and it should return with the long ground.

If you want to see a higher bandwidth signal, the Empeg has some 74LVX and RAM parts that will exceed the bandwidth of the oscilloscope.

Be very careful probing not to short pins.

Ross

Well, the spring-clip ground pins (included with the probes) help a little, compared with the alligator clip grounds (also included).

But I really cannot tell if this is just a super-sensitive scope, or if it's got a large inherent noise floor.

When switching the vertical capture resolutions, they seem to be using mechanical relays internally to switch portions of their amplifier circuit in/out.

There seem to be three vertical amplifier ranges: 100mV, 200mV, 500mV, and then, *click* 1V, 2V, 5V, and then *click* 10V, 20V, 50V. The cleanest signals, by quite a bit, are at the settings at the top end of each range, just before a *click*: 500mV and 5V.

The signal gets less noisy on the lower ranges. Eg. On the 1V range, the noise spread is often about 0.3Volts.. but zoom down to the *click* 500mV range, and the noise spread is now contained within a (approx) 150mV range.

Here's a capture off of pin-8 of one of the 74vsx04 chips, first with the spring ground tip on pin-7, and again with just the alligator clip many inches away on the empeg chassis.

EDIT: Well, that was interesting.. my CF-USB reader (for transferring photos) just tried to self-destruct -- it got *very* hot, and the chip markings inside the reader have blackened.. Switching back to the old reader now..

Cheers

Mmm.. turning off the overhead work lamp makes a noticeable difference -- it seems to account for perhaps half the noise I'm seeing on some things.

Still seems excessive to me, but what do I know?

Now I've got a 5.6VDC battery pack -- four NiMH cells in series. Aligator ground clip on one end, probe tip on the other. On the 1V/div scale, it shows a noise level of 456mV on the *DC* signal.

Which is pretty much the same noise floor it "sees" without anything connected to the probe inputs.

So now I'll skip the battery, unplug all probe leads, and just let the scope measure ambient noise with no leads plugged in, and the input set to 1:1:

Peak-to-Peak measurements of the "signal"

625-625mV at 5V/div.
667-833mV at 2V/div.
458-500mV at 1V/div.
*click*
62.5-62.5mV at 500mV/div.
66.7-83.3mV at 200mV/div.
41.7-54.2mV at 100mV/div.
*click*
6.25-8.33mV at 50mV/div.
6.67-8.33mV at 20mV/div.
5.00-7.08mV at 10mV/div.

I wonder if all of this is due to the simple plastic case that this thing is wrapped in?

Meanwhile, confirmation of my observation as to which mV/div settings exhibit the lowest noise:
The first bit about the VGA is irrelevant. But I wonder if a Tek TDS2000 really is this noisy. Anyone got one? Connect a AA battery to it, and check the noise level at 500mV/div.

??

Humn. Something I remember is that all our scopes are connected to mains with plugs without an earth pin.