mhcoen@athena.mit.edu (Michael H. Coen) (01/25/89)
Hi. Does anyone know about the Data Acquisition Unit which has been
advertised by Datel Computers in Amiga World? It's a
hardware/software package which is supposed to let an Amiga be used as
a digital scope. ($179.99, page 79, Feb. 89)
I'd like to find out more about it or something similar. Thanks.
Michael H. Coen
- mhcoen@athena.mit.edu, mhcoen%cfaip0.DECNET@harvard.harvard.edu
Claimer:
Representing the entirety of the MIT Administration. 8-)cthulhu@athena.mit.edu (Jim Reich) (01/27/89)
In article <8914@bloom-beacon.MIT.EDU> mhcoen@athena.mit.edu (Michael H. Coen) writes: >Hi. Does anyone know about the Data Acquisition Unit which has been >advertised by Datel Computers in Amiga World? It's a >hardware/software package which is supposed to let an Amiga be used as >a digital scope. ($179.99, page 79, Feb. 89) The thing looked good to me as well, until I noticed the slow conversion time. Looks like it would be fine as a Data Recorder, but pretty lousy as an oscilloscope with a 20usec max conversion rate and fairly low accuracy. Aside from the ads, though, I have not seen or heard *anything* about that company or its products. Just out of curiosity, does anyone out there know how to make a reasonably fast computer 'oscilloscope'? Even with an immensely fast DAC, I wonder what a 7Mhz computer can do as for as processing nanosecond data, which would be necessary to debug something like, say, a 7MHz computer... Can even the mighty blitter sling around data that fast? -- Jim
tomb@hplsla.HP.COM (Tom Bruhns) (01/28/89)
>Just out of curiosity, does anyone out there know how to make a reasonably >fast computer 'oscilloscope'? Even with an immensely fast DAC, I wonder what >a 7Mhz computer can do as for as processing nanosecond data, which would >be necessary to debug something like, say, a 7MHz computer... Can even the >mighty blitter sling around data that fast? > > -- Jim >---------- Well, you DON'T use the computer memory to directly put the samples in! Since you typically don't care about gobs and gobs of memory, you do it with the ADC feeding a little (1k? 2k? 32k? pick your version of little) FAST memory, then load that memory into the Amiga memory by your favorite method (make it dual-port for fastest; hose it over serial for slowest; or anything inbetween). If you have some fancy trigger logic, you can capture just what you want to look at in a relatively small memory. Note also that most very fast digitizing scopes require a repetitive waveform to operate at the fastest rate: they only get a "few" samples on each repetitive cycle, but place the samples differently relative to the start of each cycle, to build a good representation of the whole thing. Lots of tricks are played to smooth out digitizing noise, etc. Bottom line is it isn't conceptually very hard to do what you want, but will take some fairly expensive parts if you want to get real-time samples at 8 or more bits at 20 MHz or more. The computer and its graphics are a big help in the analysis and display end of things; given the samples, you can do lots of signal processing (FFT's, etc; you can even listen to the samples, played back slowly!) Tom Bruhns tomb%hplsla@hplabs.hp.com
cmcmanis%pepper@Sun.COM (Chuck McManis) (01/28/89)
In article <8947@bloom-beacon.MIT.EDU> (Jim Reich) writes: >Just out of curiosity, does anyone out there know how to make a reasonably >fast computer 'oscilloscope'? Even with an immensely fast DAC, I wonder what >a 7Mhz computer can do as for as processing nanosecond data, which would >be necessary to debug something like, say, a 7MHz computer... Can even the >mighty blitter sling around data that fast? > > -- Jim Yes, the way you build one is similar to the way you build Image processing cards :-). Get a good 12bit flash ADC (maybe two) and mount them with the front end circuitry (impedence matchers and isolation circuits) on a board with a nice signal processor such as an 56001 or 34010. Now, the sample circuit runs at say 50Mhz for good samples in the 25Mhz range and good viewing of periodic waves up to about 100Mhz.You buffer the sample memory. With each buffer being roughly 1K X 12 since that would cover a screen left to right in samples even with a A2024 monitor. Now the sample speed is on the order of 20ns per sample so you know the front end of this this will either be Cypress CMOS or 10K ECL. You can get 1K x 4 Static RAMs that will take data this fast. Actually with a decent signal processor you can run the whole system of the 50Mhz clock. Now the signal processors job is to scale the samples and in the pulse case dump them into display ram, when reading periodic samples it would probably be averaging them as well. The Amiga program would open a screen, pass a point to it's bitmap to the Digital oscilloscope board which would then dump it's data into that memory area. The rest is all fancy software. Adjusting the sample frequency, setting up trigger's versus continuous samples etc. --Chuck McManis uucp: {anywhere}!sun!cmcmanis BIX: cmcmanis ARPAnet: cmcmanis@sun.com These opinions are my own and no one elses, but you knew that didn't you.
janzen@ant.dec.com (Tom LMO2/O23 296-5421 ECL MSI Test) (01/30/89)
I don't know anything about any particular amiga oscilloscope product. However, I would like to make a general remakr about sampling oscilloscopes, which I use in my daily work. The sample conversion time places no obvious limitation on the speed of signals the scope can sample. The Tektronix 7854, until a year ago the highest performance (non-josephson) scope on the market, in terms of sampling signals of many Giga Hertz bandwidth, converts a sample in roughtly 20 microseconds. Because the samples repeat, the analog bridge can sample and "hold" a small portion of signal (some picoseconds long) and hold it for long enough for the mainframe sweep to come into position for the next ample sweep to come into position for the next sample, and convert it to digital form. Newer scopes may use 8-bit flash convertors, which are much faster, but this affects only one-shot non-repeating events, which you can't see at all on ordinary analog scopes without a long-persistance or storage screen. Tom Janzen Digital Equipment Corp 111 Locke Marlbor MA 01752