Maker Pro
Maker Pro

Random digital potentiometer driving

bertus

Moderator
Nov 8, 2019
2,792
Joined
Nov 8, 2019
Messages
2,792
Hello,

What is your intention withe the digital potmeter?
Do you want to create a random voltage?
Do you want to create a random amplitude of an incoming signal?

Bertus
 

bigkim100

Apr 17, 2013
267
Joined
Apr 17, 2013
Messages
267
What is the type of input and number of bits for the digital pot?
To be honest, I do not know, this is something that will have to be played with, as the whole thing, I am attempting to do, it start from scratch in every element of the circuit
 

crutschow

May 7, 2021
550
Joined
May 7, 2021
Messages
550
If you tell us the purpose of this random signal, we can better help you, since right now it's pretty vague.
 

hevans1944

Hop - AC8NS
Jun 21, 2012
4,780
Joined
Jun 21, 2012
Messages
4,780
Can anyone think up a way, using analogue electronics to randomly change the value of a digital potentiometer

There are many ways to accomplish what you are asking, but as others have stated, we need to know exactly WTF you are REALLY trying to DO. Being coy about this is not going to help you.

I just meant no microcontrollers
Why? Digital potentiometers are practically begging for microprocessor or microcontroller control. That would also be my preferred approach to generating a random (or more likely, pseudo-random) series of numbers... for whatever reason: time delay, electronic control, world domination, surfing... whatever.

You have to provide some REAL specifications. You can't use "what if" to design and build circuits. Just like you can't sit a monkey in front of a word processor and expect the monkey to type in anything meaningful, or even useful, to read. Well, I would not expect a monkey to perform like that. Maybe you would, so our mileage (or kilometers) may differ. Good luck with your project!
 

CircutScoper

Mar 29, 2022
300
Joined
Mar 29, 2022
Messages
300
An R-2-R ladder used as the 'pot' and clock-driven by a psuedo-random gated clock signal would work.

Well, admittedly the OP did say "potentiometer" but he might actually want a variable resistance rather than a voltage such as you can get from a ladder DAC. A digital pot does both.
 

bigkim100

Apr 17, 2013
267
Joined
Apr 17, 2013
Messages
267
This is to be used as random tuning of a radio, using a signal generator. The signal generators pot will be connected to this circuit.
 

bigkim100

Apr 17, 2013
267
Joined
Apr 17, 2013
Messages
267
If you tell us the purpose of this random signal, we can better help you, since right now it's pretty vague.
I am using a signal generator to control the tuning of a radio. I am attempting to replace the potentiometer with a digital potentiometer and have it randomly tune the radio
 

bigkim100

Apr 17, 2013
267
Joined
Apr 17, 2013
Messages
267
There are many ways to accomplish what you are asking, but as others have stated, we need to know exactly WTF you are REALLY trying to DO. Being coy about this is not going to help you.


Why? Digital potentiometers are practically begging for microprocessor or microcontroller control. That would also be my preferred approach to generating a random (or more likely, pseudo-random) series of numbers... for whatever reason: time delay, electronic control, world domination, surfing... whatever.

You have to provide some REAL specifications. You can't use "what if" to design and build circuits. Just like you can't sit a monkey in front of a word processor and expect the monkey to type in anything meaningful, or even useful, to read. Well, I would not expect a monkey to perform like that. Maybe you would, so our mileage (or kilometers) may differ. Good luck with your project!



There are many ways to accomplish what you are asking, but as others have stated, we need to know exactly WTF you are REALLY trying to DO. Being coy about this is not going to help you.


Why? Digital potentiometers are practically begging for microprocessor or microcontroller control. That would also be my preferred approach to generating a random (or more likely, pseudo-random) series of numbers... for whatever reason: time delay, electronic control, world domination, surfing... whatever.



I am using a signal generator to control the tuning of a radio. I am attempting to replace the potentiometer with a digital potentiometer and have it randomly tune the radio

You have to provide some REAL specifications. You can't use "what if" to design and build circuits. Just like you can't sit a monkey in front of a word processor and expect the monkey to type in anything meaningful, or even useful, to read. Well, I would not expect a monkey to perform like that. Maybe you would, so our mileage (or kilometers) may differ. Good luck with your project!
 

kellys_eye

Jun 25, 2010
5,289
Joined
Jun 25, 2010
Messages
5,289
I am using a signal generator to control the tuning of a radio. I am attempting to replace the potentiometer with a digital potentiometer and have it randomly tune the radio
Radio stations are at defined spacing (9/11kHz for AM, 2.4kHz for Ham Radio etc) and choosing a 'random' tuning voltage - presumably via varicap tuning - will most likely miss the stations. Tuning 'steps' in this case will have to be very 'fine i.e. many of them.
 

bigkim100

Apr 17, 2013
267
Joined
Apr 17, 2013
Messages
267
Radio stations are at defined spacing (9/11kHz for AM, 2.4kHz for Ham Radio etc) and choosing a 'random' tuning voltage - presumably via varicap tuning - will most likely miss the stations. Tuning 'steps' in this case will have to be very 'fine i.e. many of them.
To be honest, I would like to have the circuit be as sloppy as possible, so that if it misses it once, it would get it in subsequent scans
 

bigkim100

Apr 17, 2013
267
Joined
Apr 17, 2013
Messages
267
It doesn't help that you do not need that resolution. Which resolution do you need?

as an experimenter in this, Im not certain what resolution I actually need, until I get down to trying it
 

bigkim100

Apr 17, 2013
267
Joined
Apr 17, 2013
Messages
267
It doesn't help that you do not need that resolution. Which resolution do you need?

as an experimenter in this, Im not certain what resolution I actually need, until I get down to trying it
If I end up using 2017s, I will start with its 10 outputs. If that works, I will go forward in a resolution that is a multiple of 10.
 

hevans1944

Hop - AC8NS
Jun 21, 2012
4,780
Joined
Jun 21, 2012
Messages
4,780
I am using a signal generator to control the tuning of a radio. I am attempting to replace the potentiometer with a digital potentiometer and have it randomly tune the radio

That is a somewhat better description of what you are trying to DO, but it still includes an unexplained requirement on HOW to use a signal generator to control the tuning of a radio. Why is that?

I thought you wanted to select a radio receiving frequency at random? How does a signal generator do that? Not saying you cannot do that, because I know from personal experience that it is possible, but I would like to see how you plan on doing it.

As seen in recent comments above, you are still not providing enough information. In the end, it will be up to you choose to follow or adapt to whatever suggestions you receive here, but we here in the forum cannot make useful suggestions unless you tell us everything that is going on.

I am personally confused about what manually variable potentiometer you want to replace with a digitally potentiometer... is it a pot that controls the frequency of a signal generator (somehow) or is it a pot that (somehow) tunes the radio from station to station?

As I currently understand the problem, you have a radio that can somehow be tuned manually with a potentiometer-controlled signal generator. Is this correct?

Do you want to replace this signal generator pot with a digitally programmable resistor, so you can "sweep" the frequency range of the radio? This sounds a lot like the functionality of a so-called police scanner. If you have a particular radio in mind, please tell us what it is: manufacturer, model number, year it was made. Anything that would help locate a schematic for your radio. That could be very helpful in determining how to "couple" the signal generator to the radio for the purpose of tuning of the radio.

Or maybe the potentiometer in question, the one you want to replace with a digitally programmable resistor, is actually part of the radio, and you want to replace a manually-controlled tuning potentiometer with a digital potentiometer. So which one is it? The pot on a signal generator whose output somehow tunes the radio? Or the pot on a radio that you want to somehow "sweep" to select the receive frequency of the radio?

As others have mentioned, radios are designed to receive only a narrow band of frequencies within their tuning range. Broadcast AM, for example in the United States, is usually allocated a ten kilohertz band-widtrh for each station from within a broadcast band that extends only from 540 kHz to 1700 kHz. With band switches and other clever means, this passband can extended to be relatively large, but it is still finite. And broadcast stations are assigned very specific frequencies on which they may transmit and occupy radio frequency spectrum space.

In the old days, AM broadcast receivers used continuously variable tuning, so you could tune any station that had a carrier wave signal anywhere in the range of 540 to 1700 kHz. That means hobbyists could cobble together an AM broadcast-band transmitter, put it "on the air," and receive the transmitted signal with any AM broadcast band receiver. There was no need to do this on any particular frequency within the AM broadcast band because the hobbyist didn't go through the bother of obtaining an FCC (Federal Communications Commission) station license. If you were careful to use a low-power transmitter, the chances of getting caught and having hefty fines levied against you, and all your illicit electronics seized was minimal. Don't ask me how I know this.

Then along came car radios. Folks wanted to "tune in" their favorite stations while driving... risky business trying to tune a radio while keeping eyes on the road while driving. So auto makers added push-button tuning, which just mechanically memorized the last setting of the tuning dial associated with a particular button. Many years later all that was replaced with electronic tuning and the pre-select mechanical buttons were replaced with push-button switches.

My ham radio transceiver (radio receiver and transmitter all-in-one) covers a range of 310 kHz - 32 MHz and 44-54 MHz; 144-148 MHz with KX3-2M option (which I do not have). This is NOT done with just one control being used to sweep this entire range of frequencies. A range of frequencies must be selected. Even then, my radio is tuned with a knob that drives the shaft of a rotary encoder, not a noisy potentiometer. This rotary encoder selects discrete steps in frequency, as small as one hertz, but also larger steps for rapidly tuning across a band. The frequency selection is NOT continuous because this is a software-defined radio, and software is always represented in discrete binary steps. Most other radios are not built this way. Either the tuning is fixed, like with Citizens Band radios, or it is continuously variable over a range of frequencies. Amateur radio operators (hams) are not assigned a specific frequency to operate. We are allowed to operate at any frequency in any frequency band which our license authorizes. So, almost all radio amateurs use receivers that "feature" continuously variable tuning, or like mine tune in very small increments of frequency.

So again, I repeat the question: what are you trying to DO with a digital potentiometer, a signal generator, and a radio? Leave it to responders here to suggest HOW you may want to do it. After all, if you knew HOW, you wouldn't need advice from us. Maybe you really don't even need that signal generator...

So, we need to know how many different tuning steps you need, and how much tuning-frequency change each step produces.


You have no doubt noticed that your 555 timer can be wired as a free-running oscillator, with the timing controlled by a variable resistance. Perhaps it is your intention to use a digitally-programmable potentiometer to control the 555 oscillation frequency, for some purpose you have not defined.

I have found this, which is sort of what I want to do:
https://makingcircuits.com/blog/digital-volume-controller-circui/
This is a digitally-controlled attenuation circuit used as a volume control. It will NOT do what you want, vary the frequency of the 555-based oscillator. Here we do not "sort of" want to do anything. We design circuits for specific purposes using real electronic components, although sometimes we will also use computers and simulation software to see if our design is "in the ballpark," or if it even works at all, as simulated.

Simulation is not the real world. The real world is real parts connected to form a real circuit that does what it was designed to do. None of this "sort of works" is acceptable, except maybe by hobbyists with only a vague idea of HOW to accomplish their goal. Your stated goal is how to sweep the tuning of a radio in discrete but random steps using a programmable digital potentiometer. Right? If so, please tell us more about how a signal generator is supposed to tune a radio.

I used several digitally-programmable potentiometers (such as this one) in the previous century to set gain and offset parameters in an analog circuit design that was part of a personal computer (PC) upgrade of a large analog electro-hydraulic servomechanism. Those pots were non-volatile. I could set a value and then remove power from the circuit and the pot would retain whatever value I set, just like adjusting a real trimmer potentiometer, except I could do it remotely, without a screwdriver, from anywhere in the world that had Internet service. Of course remote for this particular job meant the PC was just a few feet away.
 

bigkim100

Apr 17, 2013
267
Joined
Apr 17, 2013
Messages
267
I am using the generator to tune a radio that is not using a variable capacitor, but a potentiometer (as so many are now, on inexpensive Asian radios).
This I can do successfully, and am doing right now......(I can send you pictures of this if you do not believe me...LOL).
I simply want this now to randomly tune frequencies, or at least relatively randomly ).
I know TRUE random is a long involved complicated thing to do, so an approximate thing is good enough for me...honest!.
I want to Pseudo Randomly tune the radio along the band that the radio is using.... If it lands on a dead frequently with no transmission, so be it, Im ok with that, and Ill work on that later.
So I thought, to do this, I could simply apply a APPROXIMATELY random resistance to the signal generator (the pot that I am using for tuning).
This is a VERY non standard way of doing things, and really wonky in logic, so I truly understand that this is a difficult thing for a person with a highly trained mind to understand.
Thank you to everyone for any responses that I have received so far, and will receive in the future.
 

bertus

Moderator
Nov 8, 2019
2,792
Joined
Nov 8, 2019
Messages
2,792
Hello,

What would be the voltage range needed?

Bertus
 
Top