Random digital potentiometer driving

[hevans1944]

Okay, this is starting to make sense. The signal generator currently produces a voltage that replaces the voltage produced by the tuning potentiometer in the radio. So far, so good. You now need to generate a timed sequence of pseudo-random but fixed voltages to replace the signal generator output. Did I understand correctly?

I can send you pictures of this if you do not believe me...LOL

Let's not go there. I trust that you have figured out how to connect the signal generator output to your radio without "bricking" either one. Perhaps your signal generator frequency can only be manually adjusted, perhaps it outputs triangle wave forms that slowly sweep the radio tuning up and down the band, or maybe it only outputs sine waves that accomplish the same thing, except in a non-linear sinusoidal fashion. Whatever, the signal generator isn't causing the radio tuning to jump around in a pseudo-random fashion as you want it to.

Or maybe you want to replace the rotary shaft potentiometer in the radio with a digital version that can be "dialed in" to a pseudo-randomly chosen position between minimum and maximum values. That's how I would do it. Save your signal generator for lab-bench uses, parking it next to your digital storage oscilloscope. Add a small circuit board, external to the radio, along with three small connecting wires that replace the three terminals of the existing tuning potentiometer, which you remove. Maybe you add two more wires to "borrow" some power from the radio to run the pseudo-random pot position function.

Either way, you need to decide perzactly how you are going to do this. I think the suggestion to use an R-2R resistance ladder network was a good one. The more R-2R stages you cobble together, the more pseudo-random "jumps" your "tuning" can make without repetition. Eight stages will yield 2⁸
or 256 different tuning steps. Four R-2R stages will yield 16 steps. You must decide how many unique steps you need to cover whatever tuning range you select.

The next trick is figuring out which 8-bit or 4-bit, or some other number of current-steering switches to turn on or off in your ladder network. This is the responsibility of the pseudo-random number generator. If you want to continue in this vein, we can help. There are lots of ways to generate pseudo-random numbers. Some are even based on analog "white noise" sources that are easy to construct, but more difficult to manipulate into digital number selections. And there are of course computer-based algorithms that start with a "seed" and go on to generate a pseudo-random sequence of binary numbers. These are attractive for some applications because the pseudo-random sequence repeats over some interval of time, and the same values are repeated over and over again. Very useful sometimes for statistical analysis, but probably not relevant for your application.

I wish you would allow a micro-controller or micro-processor implementation. That would be so much easier to design, albeit requiring some skills you may not be willing to learn. Your project does sound like a "fun" project, and for the avid hobbyist that is the best kind. Please let us know what we can do to help.

 

[Harald Kapp]

I wish you would allow a micro-controller or micro-processor implementation.

+1 for that.

 

[bertus]

Hello,

Have a look at this page for a random voltage generator:
https://wiki.analog.com/university/courses/alm1k/alm-signals-labs/alm-lfsr-lab
There are several resistor networks available.

Bertus

 

[kellys_eye]

Using decade counters (4017) is 'wasteful' - going binary allows the use of fewer devices but a massive multiple of the steps you can generate over a decade device.

i.e. a 2^8 binary counter (one device) gives 256 steps - this would require 26 type 4017's!

Consider a sample-hold circuit randomly driving a sawtooth waveform. You can randomly alter the timing interval of the sample/hold as well as the sweep of the sawtooth to give an 'infinite' variety of voltages. Entirely analogue!

 

[hevans1944]

IMO Posts #43 and #44 are heading in the right direction. A hardware solution is almost always "easier" to build and troubleshoot than a "complicated" computer program. I do favor the "complicated" computer program because "mistakes" are easily corrected with just a few keystrokes, assuming you know what keystrokes to make. There can be a pretty steep learning curve, but it was (and still is) a lot of fun. Never stop learning!

You have to move wires around to correct a mistake in a hardware configuration. That is the main reason that I left hardware TTL (transistor-transistor-logic) design in the mid 1970s in favor of Intel 8080 and 8085 microprocessors. There was a trade-off of slower speed for convenience and more complex control, but in our lab, speed was often secondary to performance. We didn't try to design with the latest and fastest chips available, although I did appreciate having large-scale TTL integrated circuits available if needed.

About the same time, in that era, CMOS logic was gaining traction, especially for projects requiring low energy consumption. By then I was totally committed to microprocessors, but I couldn't keep up with the programming being used for 80286 and later Intel micros, so I moved on to "IBM and IBM-compatible" personal computers, embedded in a project like an electronic component, and programmed with a structured, abstract, programming language like BASIC or FORTRAN... usually programmed by someone else, since I am not a computer analyst or even a very good "code roller." The real pros in this area went to school to learn computer science and came back with a whole bag of "tricks" about the same way electronics nerds accumulated hardware design "tricks," techniques and procedures that are totally obscure and pretty much meaningless unless you are a member of the club.

I fear that the OP who initiated this thread might be neither a computer weenie nor an electronics nerd. He is an amateur who enjoys tinkering, which (among other things) is who this forum is for. So the "solution" hinted at in posts #43 and #44 would have to be designed, built, and tested for publication by someone else. There is a "sister" forum that purports to do this: The Instructables. Go there and "monkey see, monkey do" copy at your own risk. They sometimes have useful projects, but it can be hard for the neophyte to determine what is useful and what is pure junk. BTW, Instructables is a Maker site. Some projects involve woodwork and plastic 3D printers and some skill with hand and machine tools. The projects are NOT vetted or curated.

 

[kellys_eye]

Like Hevans above (not an expletive!) I 'gave up' on programming (at least at assembly level) with the introduction of the 286 and have tried, on multiple occasions, to re-educate myself with processors using the likes of the Arduino. I find it far more pleasurable to cobble together hardware at a breadboard level and tinker until I get what I want. With coding I find myself forgetting where I'm at or what I'm trying to achieve - old age! - and invariably get sidetracked with the numerous potentials for improvement on the initial concept rather than getting on with the original concept. Distractions - another problem with age!

I do, however, recognise when I'm flogging a dead horse and have built RF analysers and programmable RF signal generators using Arduino (with LCD readout) that simply would have been 'impossible' with an analogue approach.

In the OP's example I too would look to a simple Arduino solution - with the multitude of coding libraries we have today the major part of the exercise will no doubt already have been listed by someone and cut'n'paste would finish the job a lot quicker with a lot less frustration.

Again, with the OP's idea, I don't think it's been thought through properly given the number of steps that would be required to hit even ONE station on a random basis - some form of algorithm to shorten the 'gap' period between station reception might even be an essential requirement if 'something' it to be heard in a reasonable time span.

To this end, developiing a flowchart is a pencil/paper exercise for the OP - simple resources, easily adapted, low cost! From there-on the decision to go analogue versus digital may well display itself as 'obvious'.

 

[bigkim100]

I have posted a 4017 controlled "network" (cannot think of a correct description of it at this time.)
This is the beginnings of the route that I think I will take.

Hevans has hit the perfect description of me:
"I fear that the OP who initiated this thread might be neither a computer weenie nor an electronics nerd. He is an amateur who enjoys tinkering".
Another good description of me, which is often given:
" knows just enough to get himself into trouble".

Im a 61 year old amateur, that simply dabbles, but yet always seems to come up with an answer eventually in the long run.

Is this forum not meant for people like me??

I was on another forum , but got kicked off of it because I freaked out, upset that people would rather insult my lack of knowledge, than help me with my request.

Ill go the 4017/resistor bridge route, cobble together a prototype, and see what happens.
Thank you all for your help

 

[bertus]

Hello,

@bigkim100 , I think that some of the responders in this thread are older than you.
I am 62 and more than 50 years busy with electronics.

Bertus

 

[hevans1944]

Is this forum not meant for people like me??

This forum is EXACTLY meant for people like you! And me. And @bertus. And a lot of other members you probably haven't met yet, unless you went back and read their contributions in older threads here.

I will be 78 years old if I am still alive on June 25th of next month. I have more than seventy-five years of "hands-on experience" with electricity,

I began my journey in the "study" of electricity at a very young age... about two or three years old, according to my late mother, who discovered me exploring the mysteries of two-slot convenience outlets with a silver-plated fork. Stainless steel tableware was non-extent in our house in 1946! And three-prong GFCI outlets didn't exist then either. I really only vaguely recall doing this, although I do recall the shocking sensation later when sticking a finger in a lamp socket that happened to be turned on, but without a light bulb to block inquisitive fingers. Good thing we use 120 VAC instead of 240 VAC in our convenience receptacles here in the States, but I NEVER repeated that mistake. I did learn how to make plenty of other mistakes later, such as how to let out the magic smoke, etc.

In the 1950s I began real experiments and adventures in learning about electricity, first with my paternal grandfather, who at the time was a retired West (by God!) Virginia deep-mining coal electrician living in Morristown TN. His nickname was Hickey, which is an electrician's device of many variations, bestowed upon him by his fellow miners. I was ten years old then and I haven't stopped learning about electricity, electronics, physics, chemistry... almost any "hard" science.

My biggest thrill (so far) was being put in charge of operating and maintaining a small 1.7 mega-volt tandem particle accelerator in July 1996 without any prior experience... just my knowledge of electronics and physics. I "retired" in December 2014. That job was even more exciting than working on Star Wars laser weapons research in the 1970s. Star Wars went bust for reasons I won't go into here, but particle accelerators (big ones!) went on to "discover" the then-theoretical Higgs Boson in a huge scientific collaboration at CERN, across the pond in Europe and Switzerland. There is still much to learn in particle physics and in quantum physics, but almost all the math and theory is far beyond my current comprehension. However, there is now the Internet and Great Courses Signature Collection for the layman (that's me). Can't say any of these courses will really teach you anything, like a course in electronics or computer programming would, but they do provide a overall view of lots of interesting subjects, albeit a slightly leftist view IMHO.

Most members here (drive-by posters excepted!) are diligent hobbyists who, like you, love to tinker but also have never quit learning. I believe that "tinkering" is essential for true learning. Theory is nice for objectively predicting what will happen if you do this or do that, but it is never a substitute for actually doing this or doing that. Tinkering and theory are complementary, not exclusionary, to each other. You can live a long, happy, fulfilling, and prosperous life with either one but, together, so much more can be done.

Hard work and perspiration (the Edison Way) does often eventually yield some useful result... we might all be watching television by candle light were it not for Thomas' unyielding perseverance to invent, power and distribute the incandescent lamp... but it was intellectual superiority, plus hard work, plus Westinghouse money that powered up the entire world (the Tesla Way) more than a hundred years ago. Notice it took all three to make it happen.

Elon Musk honors Nikola Tesla with the Space-X program that re-ignited the American space program. Now if only this modern, very lucky, genius would just make an electric pick-up truck that I can afford to buy... the Ford F-150 Lightning looks promising, but it is still too pricey, has a years long (or longer) waiting list, and still uses nearly obsolete lithium-ion battery technology. If Ford (or Tesla) lowers the entry-level EV price, and upgrades their expensive battery technology to an affordable price, I will install battery-backup for my recently installed solar PV array panels... well, if ever Florida Power & Light installs a net-meter so I can actually use all the solar energy that falls down freely from the daytime sky here in southwestern Florida.