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'[OT] Dumbest Circuit I Ever Built that Worked (Was'
2006\02\22@124749 by

This discussion got me to remembering way back in the Summer
of 1977 when I was a graduate student working on a special problems
project for one of my classes.  I am not an electrical engineer, nor
do I play one on TV, but I was studying to be a vocational/technical
teacher and was, as today, very interested in electronics.

I and my instructor decided that I would build a A/D D/A
converter out of readily available parts.  Time was short and so was
money so I plunged right in.  I am not sure how many A/D chips one
could buy in 1977, but I bet it wasn't many.  I hadn't yet learned
much practical information about how this process was done, but I had
an idea which actually worked.  Knowing what I do today about the
normal methods for Doing A/D and D/A, I hesitate to share this
circuit, but here I go.

The idea was to use a duel VCO chip like the Motorola MC4024
which is not a CMOS chip despite it's number.  You can connect a
timing capacitor or crystal across two pins on each oscillator section
and generate square waves.

The R part of the RC oscillator was internal to the chip and
changed as one varied the control voltage on the appropriate pin.  You
could frequency-modulate the output this way.

What I did was to set one oscillator at around 8 KHZ for the
sampling frequency and have that signal run a 74-121 chip which reset
a 12-stage CMOS counter and 7475 latches such that a new count
appeared on the pair of latches at each new sample.

The trick, here, was to run the FM oscillator at a frequency
range between 256 and 512 times the sampling rate or between 2 and 5
MHZ, roughly.  If the FM oscillator was exactly 256 times the sampling
gate signal, the counter made a complete rotation and you saw a 0 on
the output.  If it was running at near 512 times the sampling rate,
one got 255 or -xFF on the output.

Obviously, if one over-drove the input at all, a catastrophe
occurred at the output, meaning that you had to really watch signal
levels.:-)

The oscillator, if running at exactly 512 times the sampling
rate, would cause the counter to go through 2 rotations and you would
be back to 0 again.

The D/A part was equally weird.  I think I remember connecting
diodes to each TTL  output on the 7475 quad latches such that only the
source or high end voltage was present.  Each output went to a
weighted resistor such as 1K, 2K, 4K, etc and all the other ends of
the resistors went to a load resistor to ground.

It has been so long that I don't remember the finer details of
what I did, but if one fed audio in to the VCO and didn't drive the
oscillator past its proper frequency range for the counter and sample
generator, it actually produced the sort of audio one would expect
with no low-pass filter.  Speech was intelligible and had all the
fidelity of a cheap toy, but even I was kind of surprised.

The project plus a written report on how it could be done with
proper equipment and funding got me a decent grade in the course, but
I sure like the nice successive-approximation A/D converters we have
now and the PWM D/A techniques that are common practice.  Even an R/2R
ladder would have been a bit better than those weighted resistors.

Also, I remember trying to interface TTL chips with the CMOS
counter which was a real bear because TTL chips should see no more
than .75 volts on an input if that input is supposed to be low.  I
would have dearly loved to have all TTL or all CMOS at the time, but I
would sometimes put a pull-down or pull-up resistor here or there to
make things work.  Don't try this at home, kids.

Martin McCormick WB5AGZ  Stillwater, OK
OSU Information Technology Department Network Operations Group
.-- -... ..... .- --. --..
<Interesting and unusual project snipped>

>   I
> would have dearly loved to have all TTL or all CMOS at the time, but I
> would sometimes put a pull-down or pull-up resistor here or there to
> make things work.  Don't try this at home, kids.

No no no.. DO try this at home kids. It's not like it a safety issue, and
I'm willing to bet you learned a lot from the experience. You don't learn
how things work by following good engineering practices, you learn by doing
something in an obscure way that forces you to deal with the details, then
you learn the effective way to do it. It's easy to multiplex a seven segment
display in software with a PIC, but we still have students wire up a bunch
of TTL on a breadboard to see how it all works. I can buy a good
instrumentation op-amp for less than \$1, but we still teach the basics by
connecting three 741s on a breadboard.

The world needs more tinkerers and less of the "I'm a professional, don't
try this at home" mentality.

Just my \$0.02

-Denny
"Denny Esterline" writes:
><Interesting and unusual project snipped>
>
>>   I
>> would have dearly loved to have all TTL or all CMOS at the time, but I
>> would sometimes put a pull-down or pull-up resistor here or there to
>> make things work.  Don't try this at home, kids.
>
>
>No no no.. DO try this at home kids. It's not like it a safety issue, and
>I'm willing to bet you learned a lot from the experience. You don't learn
>how things work by following good engineering practices, you learn by doing
>something in an obscure way that forces you to deal with the details, then

You are right.  It's not a safety issue.  I was kind of joking
about all the cluging I had to do and how it would be hard to
duplicate the same circuit quickly.  It was a fabulous learning
exercise.

Last night, I was digging through an old box of open-reel
tape, most of it blank, but I found a reel I had recorded that Summer
of the audio output of that A/D-D/A demonstrater.  I had taken a tape
of a good-quality recording of a radio newscast along with a snippet
of music and fed it through the device and then recorded it on another
tape recorder.  So, today, my memory is refreshed as to exactly how it
or rather how bad it sounded.  I had used a 6 KHZ sampling rate
instead of 8 as I previously stated.  Mr. Myquist, therefore, would
only let 3 KHZ through.

The recording is very noisy with audible heterodynes between
the FM oscillator and the sampling gate.  There is also a strong 60-HZ
hum which was probably a ground loop between the tape recorder and the
blocking capacitor between that and the modulation input on the
MC4024.  It kind of reminded me of listening to a very cheesy digital
voice recorder with no low-pass filter at all over a badly-tuned
television set in which birdies and vertical sync hum are only 10 or
15 DB below the audio.  It was _ba-a-a-a-d._

About ten years later, I took the AC and DC circuit design
courses that OSU offered while I worked here.  All that tinkering I
had done over all these years helped tremendously in lab.  I was able
to usually make our projects work and sometimes even help fellow
students get out of jams and I think a lot of that came from the
experience of just playing with circuits.

I remember talking with my fellow students and noticing how
some of them were there because somebody told them they could earn a
lot of money.  Nothing wrong with that, but life is a lot more fun if
you do things you like and maybe you can make some money also.

This stuff is way too involved to be in if you don't really
enjoy it.  That's probably why I am not financially rich today.  I
have to be able to at least stand what I am doing.

So much for philosophy.

Martin McCormick WB5AGZ  Stillwater, OK
OSU Information Technology Department Network Operations Group

----- Original Message -----
From: "Martin McCormick" <martindc.cis.okstate.edu>
To: "Microcontroller discussion list - Public." <piclistmit.edu>
Sent: Thursday, February 23, 2006 10:33 AM
Subject: Re: [OT] Dumbest Circuit I Ever Built that Worked (Was You got

<snip>

> I remember talking with my fellow students and noticing how
> some of them were there because somebody told them they could earn a
> lot of money.  Nothing wrong with that, but life is a lot more fun if
> you do things you like and maybe you can make some money also.
>
> This stuff is way too involved to be in if you don't really
> enjoy it.  That's probably why I am not financially rich today.  I
> have to be able to at least stand what I am doing.

Martin, you are right.  I have had a ball for 69 of my 74 years doing
what I like and that is electronics. By the way I am still doing it at 74
and don't see a stopping point.   However some of us luck out and
make a lot of money doing what is fun.  I would recommend that
anyone do what he likes if it pays them enough to live on.  When you
go only for money it is usually  not much fun.

Derward Myrick KD5WWI

> So much for philosophy.
>
> Martin McCormick WB5AGZ  Stillwater, OK
> OSU Information Technology Department Network Operations Group
> --
Yup.

Bill  WB6YWI

----- Original Message -----
To: "Microcontroller discussion list - Public." <piclistmit.edu>
Sent: Thursday, February 23, 2006 1:01 PM
Subject: Re: [OT] Dumbest Circuit I Ever Built that Worked (Was You got

{Quote hidden}

>> --
Martin McCormick wrote:
>> Martin, you are right.  I have had a ball for 69 of my 74 years doing
>> what I like and that is electronics.

Out of curiosity, what did "doing electronics" mean to you back in 1932,
when you were just five years old?

Vitaliy

Combing your hair and picking up bits of paper with the comb?  Flying kites in a thunder storm?

-----Original Message-----
From: piclist-bouncesmit.edu [piclist-bouncesmit.edu] On Behalf Of Vitaliy
Sent: Friday, February 24, 2006 10:08 PM
To: Microcontroller discussion list - Public.
Subject: Re: [OT] Dumbest Circuit I Ever Built that Worked (Was Yougottoreadthis in Microchip Forum

Martin McCormick wrote:
>> Martin, you are right.  I have had a ball for 69 of my 74 years doing
>> what I like and that is electronics.

Out of curiosity, what did "doing electronics" mean to you back in 1932,
when you were just five years old?

Vitaliy

On 2/24/06, Vitaliy <spammaksimov.org> wrote:
> Out of curiosity, what did "doing electronics" mean to you back in 1932,
> when you were just five years old?

According to various timelines, the TV was just invented prior to
1932.  Vacuum tubes, batteries, radios, etc were all available at the
time.

Vitaliy;  You have it wrong I was 5 years old in December of 1936 not 1932.
Electronics was very crude by today's standards. My Grandfather along with
some other local men started a telephone company, it was a partyline type
out
in the country of southern Mississippi. As a result of this I had old
telephones
(these were the hand crank to ring type)  with which to play.  At that point
I
discovered hoe magnets and coils of wire could make electrical current flow
if
you spin the coils in a magnetic field. That was the beginning of a long
journey
that led to teaching electronics in the USA Air Force and earning a BS in
electronics(Rf and Microwave option).  I still own a small Design and
Manufacturing company and do the design my self.  To finish answering you
crystal set at that time which was fun. I also made electro magnets which I
made into a crude telegraph. I progressed from there to using the old radios
to build receivers and transmitters as well as other type of equipment.

Derward

{Original Message removed}
Vitaliy wrote regarding 'Re: [OT] Dumbest Circuit I Ever Built that Worked (Was You gottoreadthis in Microchip Forum' on Fri, Feb 24 at 14:09:
> Martin McCormick wrote:
> >> Martin, you are right.  I have had a ball for 69 of my 74 years doing
> >> what I like and that is electronics.
>
> Out of curiosity, what did "doing electronics" mean to you back in 1932,
> when you were just five years old?

I can't speak for Martin, but at that point in my life "Stomper"
trucks were popular, and I had been taking them apart and changing
motors / hooking up larger batteries for a while, as well as building
a variety of moving systems with a robot erector set (Now! With extra
sharp edges and missing bolts!).  I couldn't have been more than about
6 years old when I received one of those electronics kits which had
the spring terminals and an assortment of devices mounted on a board
(and a book with circuits - the best of which made noise).  Do "they"
still sell those things?

It took me until "Analog Signal Processing" in college - nearly 15
years later - to determine that I did not, in fact, enjoy working with
analog systems. :)

--Danny
At 03:27 PM 2/24/2006 -0500, you wrote:
>On 2/24/06, Vitaliy <spammaksimov.org> wrote:
> > Out of curiosity, what did "doing electronics" mean to you back in 1932,
> > when you were just five years old?
>
>According to various timelines, the TV was just invented prior to
>1932.  Vacuum tubes, batteries, radios, etc were all available at the
>time.
>

Vacuum tubes became practical in the 1910s and 20s:
http://www.newscotland1398.net/marconi100/marpic14.html

and the first (mechanical) television came along in the 20s, and of course
used electronics for the receiver. Cost GBP 18 at the time:
http://www.mztv.com/newframe.asp?content=http://www.mztv.com/baird.html

"I am endeavoring, ma'am, to construct a mnemonic circuit...using stone
knives and bearskins."
-- Spock in "The City on the Edge of Forever" by Harlan Ellison

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff

> On 2/24/06, Vitaliy <spammaksimov.org> wrote:
>> Out of curiosity, what did "doing electronics" mean to you back in 1932,
>> when you were just five years old?
>
> According to various timelines, the TV was just invented prior to
> 1932.  Vacuum tubes, batteries, radios, etc were all available at the
> time.

Adam, you're overthinking it, my question had no hidden meaning. Really. :)

When I turned five, I got a flashlight for my birthday. I remember taking it
apart, and twisting together small pieces of wire to see how far I can move
the bulb away from the battery, and still make it light up (not an easy task
for a five-year-old, lots of poor contacts). Then I took apart some of my
toys, and played with the motors. More interesting stuff came a few years
later in the form of crystal detectors, amplifiers, wireless mics, etc. Of
because I was born much later.

I believe that what a person does in their early childhood has a big
influence on their choice of career. For example, when my cousin was five,
he took apart his dad's motorcycle. Today he is one of the best mechanics I
know.

There is also a famous surgeon (his name escapes me), who said in an
interview that he was dissecting cats at the age of eight (under his
father's supervision).

So I guess I asked the question in order to gather more evidence for my
theory. :))

Best regards,

Vitaliy

On Feb 24, 2006, at 8:52 PM, Vitaliy wrote:

> what did "doing electronics" mean to you back in 193x

For reference, that's about the timeframe that the original
"Tom Swift" books were published (these have apparently entered
the public domain and the text is online these days.  Cool.)
Electronics as we know it today may have been a bit ... unreachable,
but plenty was possible in the realm of electricity, magnetics,
motors, electrostatics, telegraphy, and the beginnings of radio
and such...

BillW
Actually, Tom Swift pre-dates the 30's by a few years:

A bit before even my time but this is the earliest I've seen -- 1910.

Regards, Bob

And, yes, I was a huge Tom Swift fan in the 50's. All of us nerds
were. :=)

On Fri, 24 Feb 2006 21:45:51 -0800, William "Chops" Westfield wrote:

{Quote hidden}

On 2/24/06, Spehro Pefhany <speffinterlog.com> wrote:

> and the first (mechanical) television came along in the 20s, and of course
> used electronics for the receiver. Cost GBP 18 at the time:
> http://www.mztv.com/newframe.asp?content=http://www.mztv.com/baird.html
>

Mechanical television is still popular in some parts.

http://www.nbtv.org

Bill

--
Psst...  Hey, you... Buddy...  Want a kitten?  straycatblues.petfinder.org

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