Electronics related projects, information, and resources.
DSOA Mk3 - Digital Storage Oscilloscope Adapter Mk3

Yes, it's finally here !. The DSOA Mk3 has been a long time coming (many years in fact), but it was finally published in the October/November 98 issues of EA.

EA October 98 issue cover shot of DSOA Mk3

Here are the basic specs :

Screen shot of the windows software

Latest News :

Well, it looks like I was way off the mark with the design of this Mk3. Hundreds of previous users said they would love something like this, and would pay anything to get it. Well, while this may be true, it looks like no one wants to even think about building it if there isn't a full kit available. A few people have expressed interest in a short form kit, but overall the entire project is a flop :(

The major kit suppliers in their infinite wisdom have decided not to kit up for the project, apparently because it is too expensive. There has been an expression of interest from other people about doing a short form kit, but this may or may not eventuate. No matter how good this design is, it is a complete flop simply because there is no kit available.

Current Status :

This is my current stance on this project, please do not email me (or call me) and ask what the current status is, because this is the current status. If anything changes, I will change this :

What is the Bandwidth ?

There seems to be a lot of confusion about the bandwidth of a real time digital cro such as this project and the previous Mk1 and Mk2 designs. A lot of people keep asking what the bandwidth is, and seem to forget (or don't know) the basics of digital cro's. There is a big difference between sample rate, analog bandwidth, and effective bandwidth. I will clarify this situation now :

Sample Rate :

A real-time digital cro samples in real-time, ie, it takes one sample after the other. In the case of the Mk3 this is 20MHz. This 20MHz is NOT the bandwidth of the cro, it is the real-time sample rate of the analog to digital convertor.

Analog Bandwidth :

The analog bandwith is the -3dB bandwidth of the analog input amplifers and associated circuitry BEFORE the ADC. In the case of the Mk3 design, it is roughly 5MHz.

Effective Bandwidth :

The effective bandwith is a rule of thumb, which is basically 10 times less than the sample rate, or 2MHz in this case. This comes about because you need at least 10 samples per cycle of the signal you are measuring to get any decent waveform to actually view.

Now, to answer everyone's question, the effective bandwidth of this Mk3 design is roughly 2MHz, which gives you 10 samples per cycle. The analog bandwidth may be 5MHz or more, but if you try and measure a 5MHz signal you will only get 4 samples of your waveform which is next to useless. If you measure a sine wave you will see something like a triangle wave!.

If you want a real-time 20MHz bandwidth digital cro, then you need a sample rate of at least 200MHz, which quadruples the price and complexity, that's just the way it is.

For example, the new Tektronix TDS200 series real-time CRO's have a 100MHz effective bandwidth by virtue of a 1GHz sample rate. All the manufacturers are heading this way, as the interleaved sampling method (which allows high analog bandwidth with a small sample rate) is a dodgy way to do it, and manufacturers are finally learning this.

Check out my regular Electronics Engineering Video Blog

Here I am talking about Digital Storage Oscilloscope Basics:

and this one comparing PC Based oscilloscopes:


Files :

Download the DOS and Windows Executable Programs.

The complete construction article in text form.

The schematic of the analog section.

The schematic of the digital section.

The schematics in Protel format.

The operational timing diagram.

The PCB file in Protel Autotrax format.

View the PCB in 300dpi GIF format.

Component Overlay in GIF format.

Here is the Parts List

The SOURCE CODE for the DOS program (Turbo Pascal 7)

The SOURCE CODE for the Windows program (Delphi)


Please note that I NO LONGER SUPPORT THIS PROJECT in any way. Download the files and you are on your own! Really, the project is just to old for me to care any more, sorry.

Home - electronics.alternatezone.com


Copyright(c)1995-2003 David L. Jones