pocket oscilloscope

[12gauge]

I have never used an oscilloscope so I'd like to hear from people who have, about these small and affordable units like from jyetech.com .  In particular, I'd like to know if they would be useful to investigate the quality of my home made st-5 power.
RH

[BruceM]

Hi 12gauge, Glad to see you on this forum!

This doesn't look bad if the price is right.  The bandwidth is low, they claim 1MHz but since the sample rate is 5MHz that's a bit misleading.  It can really only show you a decent image of a waveform that was about 250 KHz.  The "probe" for this unit sucks- you'd have to buy an RCA to BNC adapter and then a real scope probe.  Alligator clips for both signal and ground is pathetic, and using an RCA jack sucks since then you have to spring for an adapter, too. Low frequency scope probes are so cheap that this makes no sense at all.  The basic features of the scope look good, comparable to the Vellaman.

The Vellaman single channel scopes are pretty good value for the price.  I have one that's over 15 years old, still use it much of the time even though I have a Leader 2 channel 60MHz scope, too. Their cheapest models don't do PC uploads.

http://cgi.ebay.com/Velleman-10mhz-Handheld-Oscilliscope-HPS10_W0QQitemZ330391805648QQcmdZViewItemQQptZBI_Oscilloscopes?hash=item4cece2ded0

Compare the two prices and see what you think.

Did you get the problem with your AVR fixed yet? Let me know or call me if I can be of assistance.

Bruce

[12gauge]

Hi Bruce,
Thanks for answering.  The jyetech unit is priced around $75.00.  I'm still undecided.

About my AVR, I've ordered a selection of motor run capacitors to try in my system.  I found an application note for my inverter/charger that recomends using a 50 uf capacitor on the ac input to improve power factor for the charger to work better.  Perhaps it will also get the unit to accept the power from the st-5.  I did try a 1 uf capacitor (the only one I had on hand) but it didn't make a difference. 

I'll keep at it as time and material allow.  The AVR itself is working great.

RH

[BruceM]

The price is sure a bargain.

FYI- digital scopes aren't  good for catching high frequency glitches- unless the glitch happens at the instant of the data sample, you don't see it.  In most cheap units, when you slow down the time base, they also slow down the data sampling to match, instead of showing you a vertical line of the max and min value for each pixel width of time interval.   An analog scope is much better for seeing that sort of thing...but I use my little digital scope most of the time, realizing that I may have to get out the analog scope once in a while.

Sorry the AVR still seems to piss off your inverter unit.  Some HF noise is still my best guess.  I take it turning down the set voltage didn't do any good?  

[rcavictim]

You can get some pretty darned good analog entry level and better bench scopes on epay for $75 or less nowadays. 20 MHz or better too. That would be my first choice over the digital kit you are looking at.

[BruceM]

12guage, RCAvictim is right, if you can only have one, a used analog scope would be best, because of the glitch issue.  In an analog scope you can get much higher bandwidth for the money, and often a dual trace scope, which is also very helpful for more complex situations where you need to look at a second signal relative to the first.

I'm biased towards using my Velleman digital scope more often because it doesn't aggravate my epilepsy and headaches so badly- a few minutes with the Leader scope and I'm a wreck, I have to double up on meds and drink wine to use it at all, and I quickly "get lost" and confused.

My old Velleman is unique in having fairly low EMI. It is +-4.5V powered straight off of AA batteries- NO switch mode DC-DC converters at all, and no pulsing current to LED backlight.  It's really an obsolete design POS, but for me, because of it's low emissions,  it is very useful.

Where the digital scopes shine is for the "one shot" data capture modes;  for example, when I wanted to catch the peak voltage coming out of my ST-3's harmonic windings during a motor start surge, I hooked up the Velleman and set it up for a one shot data capture with a rising trigger voltage over 200 volts.  Then I set up the "event" (generator running, turned on my 1/2HP submersible pump) while the Velleman was watching and waiting for the trigger.  Sure enough- it caught a peak of almost 400V (using a scope probe set to x10). 

Digital scopes are also invaluable for low frequency stuff- you'll go blind trying to look at 10Hz Lister flicker on an analog scope- a trace flashing at 10Hz just isn't readable.  The digital scope can capture it and you can review a stable image- it doesn't have to be something fixed in frequency, and it doesn't have to happen more than once.

[12gauge]

Thanks for the input guys.  It all gives me ideas and helps me digest this.  Bruce, I haven't been back to the cabin yet so I haven't tried turning down the voltage yet.  Hope to return soon after I get my order of capacitors.
RH

[BruceM]

Let me know how it goes with the AVR, 12Gauge.  Phone is fine.

[rcavictim]

Here ya go!  Dual trace too!  Hurry, last day.

http://cgi.ebay.com/VINTAGE-BALLANTINE-1066B-20MHZ-DUAL-TRACE-OSCILLOSCOPE_W0QQitemZ180473811277QQcmdZViewItemQQptZBI_Oscilloscopes?hash=item2a0513d14d

[BruceM]

Price reflects the fact that it is not guaranteed to work.  I'd rather pay a bit more. 

[rcavictim]

Price reflects the fact that it is not guaranteed to work.  I'd rather pay a bit more.  

Hey, it lights up both traces.  What else do you need?  

Actually  I have a Gould 2-channel that is remarkably similar to that one and use it on my audio workbench and on tesla coil tuning.  It has been solid and reliable if simple and basic.  No complaints.  

Forgive that I am a tight wad.  My financial life is such that I must perform miracles with pennies or do without.  I'm used to thinking that way automatically and for that reason figured this scope was a deal worth exploring.  I would have moved on that 'deal' had I needed an extra scope, maybe one for the kitchen.    Don't laugh.  I bought an air compressor at Princess Auto because it was just the right size for the kitchen.  That's what I told the salesman.  OK laugh. 

A year or so later the same compressor was up on sale again and I was in the store and saw a farmer and his wife looking at this model and discussing it with the salesman.  I mentioned that I had bought one and was very happy with it (I am), and that the reason I had bought it was because it was "just the right size for the kitchen".  They got a good laugh out of it.  I actually do either keep it in the kitchen or the laundry room (for convenience) and I grab it when I need to fill a tire somewhere on the property.

[mobile_bob]

i gave 55 bucks for a B&K 20mhz 2channel scope a couple years ago, off of craigslist

i am very happy with it, it does all i need

there was a time not so very long ago, that a 20mhz scope was something only folks like nasa, or bell labs would have


bob g

[BruceM]

I was a very lucky youngster- as a 19 yr old my employer at the AF research lab where I worked 39.9 hrs a week while going to college would let us sign out most test equipment over weekends.  I got to use $60K+ Tektronics scopes (calibrated annually and certified) for home projects. 

I've been burned before on the "I powered it up and it looks ok but I have no way to test" sales pitch.  I've seen guaranteed OK, decent brand dual trace scopes on Ebay for $50-75.

[rcavictim]

I was a very lucky youngster- as a 19 yr old my employer at the AF research lab.....

Wow Bruce, you worked in AUDIO FREQUENCY research?  Cool!    Just pulling your leg....unless you actually did and if you did, that is cool.

I've been burned before on the "I powered it up and it looks ok but I have no way to test" sales pitch.  I've seen guaranteed OK, decent brand dual trace scopes on Ebay for $50-75.

I like the one, "The power cord doesn't look safe so I can't plug it in and test it".  When you see that assume a parts machine or something that requires a full electronic restoration.  When buying vintage TV sets or tube audio from the 1940's through early 60's it is actually just as well the seller not 'plug it in' as this is a good way to fry probably recoverable/reformable electrolytic caps in the power supply circuits.  I collected a good number of vintage round screen TV's from the 40's and the earliest color receivers from the 50's, also round screen as a hobby interest and had a lot of fun bringing some of them back to life, especially the color sets. Most I didn't touch figuring they will be much more valuable to any collector 50+ years from now unmolested if by a miracle they survive.  I costs money to climate control store treasure like this.  It is absolutely amazing what the engineers were able to do with just 20 or so vacuum tubes when you consider a TV set today contains the solid state equivalent of thousands of vacuum tubes!

When I was a young teenager there was a radio TV repair shop in Vancouver where I had befriended the technician and he had a vintage even then, RCA 3" o-scope on the shelf.  I wanted that thing so bad.  I saved and saved and eventually got it for about $15, a small fortune at the time for a kid when allowance was like 50 cents a week.  I wish I had kept that.  It was a prewar scope, RCA's first model. TVM-122.  I was building tube amps on hand worked aluminum chassis and tearing apart radios and TV's for parts and to learn when I was 12.  As an adult past middle age I haven't changed a bit! 

[BruceM]

As you suspected, by AF I meant USAF. But I did do audio work- one of my early assignments (age 19) was an audio simulation for the A-10, aka "the flying bathtub", aka "Warthog".  We did the first A-10 simulator, a crash project after some literal crashes, later used for the first ever combat mission training research.

I had good audio spectrum data for most of the sound, so programming the sound generator hardware wasn't hard; engine noise, air handler, canopy air roar, etc.  But I had no data for a touch down tire screech, so I had to guess at some parameters. My first attempt, before I was allowed to adjust the various parameters, sounded like someone stepping on a rubber ducky. It got howls of laughter.  I was never allowed to change it, as the TAC pilots insisted on keeping it as it was. I left the operations console area whenever a landing was going to occur, as inevitably there would be laughter and pointing my way.