Re: Historical Analog Scope Triggering Techniques

Harvey White

Thank you.

Many years ago, I was working on TTL stuff with a 513D scope.  I needed to look at multiple traces on a somewhat limited scope.  I took the trigger output (I think), reduced it to a TTL pulse per sweep, ran that to a binary counter, then to an 8 to 1 multiplexer.  The output of that multiplexer drove a common base summer that used the 4,2 and 1 outputs from the counter as 8,4 and 2 inputs to a homemade (crude!) D/A converter with the multiplex output going to the 1 input on that A/D.

Essentially, I got 8 traces time multiplexed onto 1 trace. Worked for TTL only, but that's what I needed.


On 12/4/2020 10:58 AM, Tony Fleming wrote:
Harvey I know this isn't the place to thank you for helping everyone, but I
wish you Happy Holidays and lots of health & love!
And thanks for helping me with my Tektronix scope!!!
I also like to wish you all Happy Holidays and best 2021!
Let's all love each other!
Let's find common ideas and be willing to listen to others!

On Fri, Dec 4, 2020 at 9:46 AM Harvey White <> wrote:

That or a CPLD, which has less capability and less cost. They're easier
to use if you're making your own boards, but you'll need a programmer,
so additional cost. Remember that while a CPLD has non volatile memory
for the configuration, most FPGAs don't. That should be included on the
development board, and if you're lucky, so will the programmer. Typical
FPGA downloads a pass through program into the FPGA, uses it to program
the memory, then programs the FPGA from the external memory. That
reprogramming is automatic (or can be) when power is applied to the board.

You'll want to program in either VHDL or Verilog, although I personally
prefer VHDL.

A critical part of the design is that regardless of CPLD or FPGA, the
I/O voltages are ONLY 3.3 volts, and you *must* level translate. There
are chips good for that, though, and you only need one way.

An arduino, touchscreen display, programming, and some sort of interface
to the CPLD/FPGA would set up triggering conditions. Do note that the
FPGA can support a more complex (I2C or SPI) interface, and THAT needs
to be level translated too.

Nice project.

The simpler design would be some dipswitches, 74LS86, 74LS30. One switch
for 1/0, one switch for "don't care". But where'd be the fun in that?


On 12/4/2020 9:30 AM, wrote:
On 2020-12-04 2:31 a.m., Jeff Dutky wrote:
Okay, this is all in line with what I've been thinking about: building
a little box that can raise a TTL output on various conditions like a
specific counter bit, or having a 16 bit input value between two selected
values, or when certain bits are set or cleared, etc. It seems like this
would make all kinds of things visible on a simple analog scope at
relatively little cost (assuming that you don't want to do the triggering
at clock rates much above a few tens of MHz, of course).
I would consider a tiny FPGA rather than discrete TTL, which would give
you thousands of gates of logic reconfigurable without soldering. You
can get a suitable dev board for ~ $20.

One of the things that I was trying to do with these scopes, before I
got side tracked having to fix them, was to reverse engineer the digital
interface to a gas plasma display in an old laptop. Getting anything more
than a very general look at the display signals was very challenging,
especially since I didn't understand most of the scope's features very
well, but also because I just wasn't thinking clearly about how to trigger
the scope and one what. After working on these scopes for the past month I
think I'm beginning to get a better feel for what they can do and how they
should be used.
-- Jeff Dutky

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