test equipment / Re: Z80 / Z84C Swap (Doh!)

Dave G4UGM dave.g4ugm at gmail.com
Tue Aug 18 04:03:58 CDT 2015

The videos below are from 2009 so are now 6 years old, so about the same age as windows/7. I don't know of any modern USB scope that does equivalent time sampling. Memory Depth isn't so important as USB2 means you can shift the data pretty quickly into the PC.

I also note he says proudly he doesn’t have a PC in is lab. I have several and they are really useful for many things. In 2009 I probably didn't, but these days they server as audio signal generators, audio frequency counters, and Audio oscilloscopes. with a DVB memory stick inserted they provide low cost, reasonable quality spectrum analysis. As for displaying the scope output how many scopes have a 14" screen. Those with a reasonable cost all have smaller screens where 8-bit sampling is probably OK. Note the Rigol he proudly trumpets has a 5.7" display. Yuk!. I also have recording 3.5 digit DVM with a USB interface. Good for recording data over short periods....

As he says for us with higher speed devices you probably want a 20Mhz displayable bandwidth, so I would say 80mhz sampling Minimum, he says 200Mhz, but for older vintage stuff you are seldom going to be going that fast. I own a DSO5200 as mentioned in the videos and its great, but the only time I have used its full abilities was to test a 0-30Mhz Direct Digital Synthesis frequency generator I built.  I actually recently went and bought a 6022 as well. At the price I just don't worry about it, I throw it in the laptop bag and away I go.

Well 12-bit is, imho a total waste of money for Computer Restoration or really most work. That’s equivalent to about 250 microvolts on a 0v to 1volt signal. I could see an argument for 10-bit which is about 1 millivolt on a 0v to 1volt signal, but that’s the most you can display on a 1168x1024 screen and even then you won't fit it all in as you will have some borders. (Double those figures for  symmetric +/-1volt audio) 

As someone else said 8-bits resolution is 4 pixels  on a modern screen, but this laptop so that’s how far the signal jumps. If you go for analog scopes then the screen size will be significantly smaller so you won't get anywhere near that resolution, and even on a very good scope I am pretty sure the spot size will be greater than 1 pixel. This laptop, which is typically what I use the USB scopes with is actually only 900 pixels vertically so about three pixels per step.

Lastly I also own 2 analogue scopes, both old, a Tektronix 453 and a "no name" TV engineer scope that our local college sold when it stopped teaching TV repair. There are times when both of these are useful, but if I had to choose then I would take either of the USB scopes any day.

In short I guess it is all down to what is called "opportunity cost".  Spend $60 on a scope and the fastest CPU you can debug will be an 8Mhz z80 or 8086. For $200 you are in the higher speed 68030 arena...


> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Jay Jaeger
> Sent: 18 August 2015 03:55
> To: cctalk at classiccmp.org
> Subject: Re: test equipment / Re: Z80 / Z84C Swap (Doh!)
> You might check EEVBLOG on Youtube.  The guy's a blast and covers what
> you are asking about.  He indicates 8 bits is really not to his liking at all, to go
> for more.  He also goes over the sampling rate of some of the USB DSO's out
> there.
> EEVBlog #13:
> https://www.youtube.com/watch?v=JTG6jWL0ZqA
> https://www.youtube.com/watch?v=Ev121xAt_k4
> On 8/17/2015 6:15 PM, drlegendre . wrote:
> > Hey Dave & All,
> >
> > Could you give a little quick kick-start guide to bit depth & sampling
> > rate on DSOs? It's always kind of stumped me, not that I've ever read
> > deeply into it.. but how is it that you can get any kind of (vertical,
> > right?) resolution out of 8 or even 12-bit samples?
> >
> > Example line of thought - 8 bit sample = 256 possible vertical positions.
> > Even if the screen is low-end (640 x 480) that's almost 2X more height
> > in pixels than samples in an 8-bit sample. So each increment is like 2
> > pixels tall and seems like it would be awfully blocky and imprecise.
> > Things would seem to get even worse if you try to do maths functions..
> >
> > I must be viewing this quite wrong?
> >
> > On Mon, Aug 17, 2015 at 3:55 PM, Dave G4UGM
> <dave.g4ugm at gmail.com> wrote:
> >
> >>
> >>
> >>> -----Original Message-----
> >>> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of
> >>> Noel Chiappa
> >>> Sent: 17 August 2015 21:12
> >>> To: cctalk at classiccmp.org
> >>> Cc: jnc at mercury.lcs.mit.edu
> >>> Subject: Re: test equipment / Re: Z80 / Z84C Swap (Doh!)
> >>>
> >>>     > From: Eric Smith
> >>>
> >>>     > If a person has any reasonable business justification
> >>>
> >>> But a lot of the people here don't; they're purely hobbyists. So
> >>> spending
> >> $1K
> >>> on a piece of test equipment just isn't realistic for them.
> >>>
> >>> Having said that, I do see some DSO's on eBay for not much money (e.g.
> >> the
> >>> little hand-held ones), and those might be a good alternative to a
> >>> logic analyzer - I never used one, so I tend not to think of them.
> >>>
> >>>       Noel
> >>
> >>
> >> I haven't tried the dedicated DSO's but I have a couple of USB
> >> connected ones and a laptop. For value for money I don't think the
> >> Hantek 6022  can be beaten. It really only goes to 8Mhz but I see
> >> they can be had for $60 - $70 and some sellers have US stock.  I also
> >> have a 200Mhz one but to be honest for 99% of vintage stuff the
> >> Hantek is fine. It is only 8-bit, it is a bit noisy, but its small
> >> enough to slip in the laptop bag, it doesn't need a separate PSU...
> >>
> >> Dave Wade
> >> G4UGM
> >>
> >>
> >

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