Author Topic: Velleman HPS140i miniature DSO - a thing of beauty or ugly duckling ?  (Read 32004 times)

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Offline saturation

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Re: Velleman HPS140i miniature DSO - a thing of beauty or ugly duckling ?
« Reply #30 on: March 22, 2011, 11:14:09 PM »
Great review, mike, shows how they managed to reduce costs as much as possible.  The only thing left to see is its actual frequency response.

The battery rests on the PCB with sponges; those sponges deteriorate in a few years but its easy to replace.  Looks like it could rattle sometime in the future and bump against the casing.  The HPS40 series have batteries cradled in their own plastic shell, firmly held down by the screw case, but enlarges the size much.  Practically however, not sure how either design is better drop proofed, the 140 has the sleeve to absorb some shock while the HPS40 has a better more rigid case.  The supplied carry bag gives it drop-shock proofing for transport though, and a container to stash the probes and an wall wart, if you have one.
 

OK folks teardown time : http://electricstuff.co.uk/velleman_hps140.html

No real surprises there. Pity about the crude battery management.
(Ignore original comments re. time measurememt - hidden in additional menu..!)

Best Wishes,


Saturation

Offline mikeselectricstuff

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Re: Velleman HPS140i miniature DSO - a thing of beauty or ugly duckling ?
« Reply #31 on: March 23, 2011, 12:42:50 AM »
Great review, mike, shows how they managed to reduce costs as much as possible. The only thing left to see is its actual frequency response.
will check this soon
Quote
The battery rests on the PCB with sponges; those sponges deteriorate in a few years but its easy to replace.  Looks like it could rattle sometime in the future and bump against the casing. 
yes - they should have used high-density foam, although the case isn't really rigid enough to be able to apply too much clamping pressure, so this may be the reason for the thin foam. Some double-sided sticky pads would probably be better.
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Offline mikeselectricstuff

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Re: Velleman HPS140i miniature DSO - a thing of beauty or ugly duckling ?
« Reply #32 on: March 23, 2011, 10:10:51 AM »
A quick play with a signal generator reveals this unit has limited usefulness above 1MHz - abote this, trigger becomes jittery, and there are some aliasing issues. I have seen the auto-scale lock onto an alias, which can produce some rather bizarre trace displays!
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Offline Aurora

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Re: Velleman HPS140i miniature DSO - a thing of beauty or ugly duckling ?
« Reply #33 on: March 23, 2011, 10:45:33 AM »
Mike,

Thanks for doing the teardown and test for us.

Interesting findings. I presume you were presenting the unit with a square wave as if it's unhappy above 1MHz with a sine wave I would be really surprised. Thanks to your details of the ADC (ADC0801S040) we can see that the device was designed for video AD conversion and has an analogue bandwidth of around 10MHz with a Max sample rate of 40MHz. That may explain why it provides a decent enough image of 6MHz CCIR CCTV signals.

Most of my work is in the analogue domain with occasional journeys into the world of 1's and 0's so this little scope should be fine for me. Not so sure about it being useful in the world of fast microprocessors though.

I see your unit has the same capacitor mod as mine. I wasn't that impressed with the physical implementation of the mod but I suppose if it works OK it does the job well enough. It was nice to see the relay's present on the PCB. Like you, I find the absence of a managed charge circuit and any 'battery low' indication a disappointment. It doesn't cost very much to include such features these days.

All in all, I am very pleased with my purchase and have already used it several times as it is just as convenient as grabbing my multimeter off the desk, and so quick to use. The very compact size makes all the difference for me in terms of convenience. The serious stuff will still happen in the lab with my bench scopes but the little HPS140 has now ousted my UNI-T UT81B from it's perch as the 'grab & go' scope  :D

Offline mikeselectricstuff

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Re: Velleman HPS140i miniature DSO - a thing of beauty or ugly duckling ?
« Reply #34 on: March 23, 2011, 11:08:35 AM »
Mike,

Thanks for doing the teardown and test for us.

Interesting findings. I presume you were presenting the unit with a square wave as if it's unhappy above 1MHz with a sine wave I would be really surprised.
Nope. Sinewave. trigger jitter is the first problem you see. Amplitude starts nosediving around 6MHz.
Quote
All in all, I am very pleased with my purchase and have already used it several times as it is just as convenient as grabbing my multimeter off the desk, and so quick to use. The very compact size makes all the difference for me in terms of convenience. The serious stuff will still happen in the lab with my bench scopes but the little HPS140 has now ousted my UNI-T UT81B from it's perch as the 'grab & go' scope  :D

Actual usefullness is always the ultimate test, but I think omission of frequency/period/RPM measurement was a major missed opportunity.
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Offline saturation

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Re: Velleman HPS140i miniature DSO - a thing of beauty or ugly duckling ?
« Reply #35 on: March 23, 2011, 08:46:58 PM »
Ouch.  Sorry to hear, I was looking forward to this as potential replacement for my HPS40 should it get bricked.  Test waveform is sine wave > 1 MHz and up?  I'll post HPS40 screen grabs.

Aurora, Mike's quick test is another good reason to compare frequency response to the Uni-T 81.
Mike,

Thanks for doing the teardown and test for us.

Interesting findings. I presume you were presenting the unit with a square wave as if it's unhappy above 1MHz with a sine wave I would be really surprised.
Nope. Sinewave. trigger jitter is the first problem you see. Amplitude starts nosediving around 6MHz.
Quote
All in all, I am very pleased with my purchase and have already used it several times as it is just as convenient as grabbing my multimeter off the desk, and so quick to use. The very compact size makes all the difference for me in terms of convenience. The serious stuff will still happen in the lab with my bench scopes but the little HPS140 has now ousted my UNI-T UT81B from it's perch as the 'grab & go' scope  :D

Actual usefullness is always the ultimate test, but I think omission of frequency/period/RPM measurement was a major missed opportunity.
Best Wishes,


Saturation

Offline mikeselectricstuff

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Re: Velleman HPS140i miniature DSO - a thing of beauty or ugly duckling ?
« Reply #36 on: March 23, 2011, 09:50:29 PM »
Here's a vid showing response from 1-10MHz.
 
Velleman HPS140 pocket scope
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Offline saturation

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Re: Velleman HPS140i miniature DSO - a thing of beauty or ugly duckling ?
« Reply #37 on: March 23, 2011, 10:15:14 PM »
G'morning mike from NE USA.  You beat me to it!  You are fast.  That response is much like the HPS40, its not too bad.

I agree fully to 1 MHz, its at its best.  Between 1-4MHz, is 'ok', and above 4 MHz, you need to read between the lines. If I saw anything above 10 MHz, I better open the windows and make sure my glue containers are shut tight  ;D.   Given its 40 MHz clock and sampling rate, I limit its use to 4MHz and below.

Since the PIC MCU uses its internal oscillator, I think jitter is heavily part of the low internal clock stability, but above 4 MHz or so, the sampling rate increasingly plays havoc on waveform stability since its can't trigger at the right levels consistently.  Square waves are stable at 1~3 MHz, to suggest its able to lock in a bit better on step responses than sine.
Best Wishes,


Saturation

Offline mikeselectricstuff

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Re: Velleman HPS140i miniature DSO - a thing of beauty or ugly duckling ?
« Reply #38 on: March 23, 2011, 10:49:17 PM »
Since the PIC MCU uses its internal oscillator, I think jitter is heavily part of the low internal clock stability
I don't think so, as if it was clock jitter you'd see waveshape distortion - the magnitude of the trigger jitter is way more than any visible distortion of the waveform - when frozen the waveform looks pretty uniform.
Assuming the triggering is done via a seperate path to the ADC signal processing, it's more likely some variable-latency issues and/or limited performance of the trigger hardware, which I assume is that LMV934.
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Offline Aurora

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Re: Velleman HPS140i miniature DSO - a thing of beauty or ugly duckling ?
« Reply #39 on: March 24, 2011, 04:35:49 AM »
Mike,

Regarding frequency and period measurement... did you mean dynamic or static measurement ? The HPS140 does offer frequency and period measurment of a static signal in the 'Hold' condition by use of the markers.

Offline mikeselectricstuff

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Re: Velleman HPS140i miniature DSO - a thing of beauty or ugly duckling ?
« Reply #40 on: March 24, 2011, 04:38:18 AM »
Mike,

Regarding frequency and period measurement... did you mean dynamic or static measurement ? The HPS140 does offer frequency and period measurment of a static signal in the 'Hold' condition by use of the markers.
Yes, but it would be so much nicer, and entirely feasible, to have it do automatic freq, period, pulsewidth, duty cycle, RPM  measurments as well for no extra hardware cost, which would make it so much more useful.
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Offline Aurora

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Re: Velleman HPS140i miniature DSO - a thing of beauty or ugly duckling ?
« Reply #41 on: March 24, 2011, 04:56:09 AM »
Agreed  :)

I have just run my HPS140 through the same test as you and can confirm mine bahaves in exactly the same manner. If I am totally honest I am disappointed with the triggering performance  :(  Lots of jitter above 1MHz. Using 'Hold' provides a clearer image but I expected the waveform distortion due to aliasing errors to cut in before triggering started to let go.

If I were writing a report on the HPS140, I would say 'could do better'.

I will have a quick look at how my UT-81B behaves and report back.

UPDATE:

A quick test of the UT-81 wiped the floor with the HPS-140..... ho hum  :(

I have an acceptable trigger stability on a sine wave being displayed at 12.8 MHz (yes 12.8MHz). There is some jitter but nowhere near as bad as on the HPS-140 at 2MHz ! The UT-81 is suffering attenuation at 12.8MHz of course but the display is stable enough for assessment.

I guess this either makes the UT-81B a good performer or the HPS140 a FAIL  :-[

More when I have time.
« Last Edit: March 24, 2011, 08:00:27 AM by Aurora »

Offline Aurora

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Re: Velleman HPS140i miniature DSO - a thing of beauty or ugly duckling ?
« Reply #42 on: March 24, 2011, 06:14:35 AM »
I'm starting to think the HPS-140 has a design fault as the triggering is so unstable above 1MHz whereas the UT-81B is far more stable.
I have just completed some tests and pictures will follow. It is safe to say that the UT-81B is a far superior product in terms of it's trigger lock and bandwidth. I'm gutted  :(  I can tolerate compromise but this may be a step too far. An email to Velleman may be in order to ascertain how well they expect the unit to perform.
« Last Edit: March 24, 2011, 07:59:18 AM by Aurora »

Offline Aurora

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Re: Velleman HPS140i miniature DSO - a thing of beauty or ugly duckling ?
« Reply #43 on: March 24, 2011, 07:32:18 AM »
Ok I quickly did a comparison between the HPS-140 and the UT-81B.

The test setup used a Grundig/Digimess FG100 20Mhz Function Generator (this uses a MAX038 core). The function generator was working into a 50 Ohm through termination then split using a common BNC T piece feeding the two oscilloscopes via 25cm RG58U patch cables. Both oscilloscopes should see the same signal but it is acknowledged that the T splitter is less than ideal in terms of impedances etc.

I presented the oscilloscopes with a square wave and photographed the displays at various frequencies. The results are shown in the pdf attachment. The 10MHz and 15 MHz signals were Sine waves and I was just interested to see how the UT-81B coped with the higher frequency signals.

With regard to jitter.... both oscilloscopes displayed very minor jitter at the lowest frequencies due to minor sampling point tolerances, The UT-81B maintained a stable and well triggered waveform display up to beyond 13MHz with jitter becoming an issue at 15MHz. The HPS-140 displayed minor waveform jitter at 1MHz and was becoming unstable at 2MHz, increasing to unacceptable jitter at 4 Mhz. HPS-140 triggering was lost at 5MHz.

Rise time measurement at 1MHz was not possible due to the limitation of the timebases (100nS/Div on UT-81B and 25nS/Div on HPS-140)

It would be fair to say that the HPS-140 is a compromise (compromised?) solution to achieve small size. It is for potential purchasers to decide if it is compromised to the extent that it loses credibility as a 40 MS/s 4MHz BW DSO. I shall be using mine for quick checks to ascertain the presence and level of various sub 4MHz signals. I am still disappointed at the trigger performance however, and shall be raising this with Velleman.
« Last Edit: March 24, 2011, 07:57:21 AM by Aurora »

Offline saturation

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Re: Velleman HPS140i miniature DSO - a thing of beauty or ugly duckling ?
« Reply #44 on: March 24, 2011, 07:49:59 AM »
Wowza.  Thanks so much for doing these Aurora, Mike, and the commentaries too.  I keep thinking of the 140 as the same as 40 but there are differences, AFAIK.  Will duplicate your tests as you did and post my results.   Comments later. 
Best Wishes,


Saturation


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