POV Clock + LED multiplexer

Hello,

During the last few days, I was interested in the POV system (especially the clock that allows you to show text or image). So I'm currently thinking about making one.

Despite, I'm a hobbyist ! I'm just an IT student who understands the basis of Arduino. I only made some test stuffs with leds, LCD display, Humidity sensor, 220V relay, etc.

So, I've seen a lot of videos / articles about simple POV clocks. In general, the clock is made from more or less 16 leds.
But, I want to have more leds. Maybe something like 30/40 leds. Furthermore, I'd like them to be RGB.

Last point, but not the least, I want to be able to power the rotating part without contact. In fact, I don't want to be annoyed changing the battery all day...

So, here is my question : Is it possible ? What are the important point that I have to pay attention ?

For a POV system, the time is very important. I'm just afraid that the multiplexing part is too slow for the system...

Thank you in advance,

Zeblood

Zeblood:
For a POV system, the time is very important. I'm just afraid that the multiplexing part is too slow for the system...

You are correct. Multiplexing is out of the question - and NeoPixel RGB LEDs are probably impractical also.

Thank you for the response.

What can be possible so ? Is there any solution in order to get more than around 16 leds ?

Paul__B:
You are correct. Multiplexing is out of the question - and NeoPixel RGB LEDs are probably impractical also.

I wouldn't say multiplexing is out of the question. It depends what that means and what is being done and how it is being done.

Zeblood,
one thing you might want to consider is that you can do some spectacular displays with much less than 30/40 LEDs.
Google around for bicycle POV. There are many arduino projects out there and some of them have animations or even full color images.

There are also some new style LEDs that use SPI vs the NeoPixel signaling so they are much faster to update.
Here is a sample project from adafruit: https://learn.adafruit.com/bike-wheel-pov-display/overview

IMO, the hardest part will be handling the power. I've seen some POV clocks that have done it.

Here is a really cool project that didn't use batteries, used 40 leds and used 595 shift registers for the multiplexing:

And another one that used neopixels and 595 shift registers to drive them:
http://leyanda.de/index.php/main/pov-globe

If you google around you can find some globe/spherical POV kits that provide all the electrical and mechanicals.

--- bill

bperrybap:
I wouldn't say multiplexing is out of the question. It depends what that means and what is being done and how it is being done.

I disagree. Neither of the projects you cite multiplexes the LEDs, nor do they use NeoPixels. :astonished:

Of course, POV display is of course inherently a mechanical form of multiplexing, but not electrical multiplexing of LEDs as used in matrix displays.

Paul__B:
I disagree. Neither of the projects you cite multiplexes the LEDs, nor do they use NeoPixels. :astonished:

In terms of "multiplexing" I said: "It depends what that means..."
Any by "that" I meant multiplexing.
In my view using 595 shift registers to control a bunch of LEDs using a small number of pins is multiplexing.

In terms of projects, I mentioned 3 projects not just 2.

I never said any of them used NeoPixels.
On the first project, I mentioned Neopixels, but I said it used a new style of LEDs that uses a SPI interface which is faster than the neopixel signaling interface.

Of course, POV display is of course inherently a mechanical form of multiplexing, but not electrical multiplexing of LEDs as used in matrix displays.

POV does not require anything mechanical or physical movement.
For example, CharliePlexing does not use any mechanical movement, but yet uses electrical multiplexing and persistence of vision.

In order for things like these spinning POV displays to work they need positional and time based electrical multiplexing of the LEDs to control where/when they turn on.
i.e. not only is there electrical multiplexing but the multiplexing and LED control is dependent on the position of the leds, which changes through time.

--- bill

OK, we are talking at cross purposes.

Suffice it to say:

bperrybap:
I never said any of them used NeoPixels.

bperrybap:
And another one that used neopixels and 595 shift registers to drive them:
http://leyanda.de/index.php/main/pov-globe

:astonished:

Paul__B:
OK, we are talking at cross purposes.

Perhaps. Maybe? Not sure…
My assumption was that “multiplexing” meant controlling the LEDs using a small number of pins.
i.e. using less Arduino pins than LEDs.

Suffice it to say:
:astonished:

Yep, are correct my bad. That last one actually doesn’t use neo pixels. Just three 595 shift registers to drive 8 red, 8 green, and 8 blue LEDs.
No clue why I typed that it used neopixels and then failed to even see it later/afterwards. :blush:
Slap me with a wet noodle.

But the main point I was trying to make was that all of them are doing some sort of multiplexing to control the LEDs with a small number of Arduino pins rather than controlling each LED directly with a seperate Arduino pin.

The reason for pointing this out being that it sounded like you had previously stated that multiplexing was out of the question.

— bill

When someone refers to

Zeblood:
In general, the clock is made from more or less 16 leds. But, I want to have more leds. Maybe something like 30/40 leds. Furthermore, I’d like them to be RGB.

I tend to think the “multiplexing” to which they refer, is what we often do to drive many LEDs with few driver connections, such as arrays.

And this sort of display multiplexing is clearly not compatible with a “POV clock”. :astonished:

I doubt the OP even dreams of using shift registers or I2C expanders to expand I/O as “multiplexing”. I most certainly do not. :roll_eyes:

Paul__B:
I doubt the OP even dreams of using shift registers or I2C expanders to expand I/O as “multiplexing”. I most certainly do not. :roll_eyes:

Which seems odd to me given that multiplexing simply means a way of sending multiple signals or streams of information over a communications link at the same time in the form of a single, complex signal; the receiver recovers the separate signals, a process called demultiplexing (or demuxing).

But all this goes back to the very first thing I said back in post #3:

I wouldn’t say multiplexing is out of the question. It depends what that means and what is being done and how it is being done.

i.e. if the classic definition of multiplexing is being used, then yes multiplexing is not out of the question since there are some forms of multiplexing that are very fast and efficient.
But if a persons view of what “multiplexing” means is more narrow, then all bets are off since it might only include various forms of multiplexing such as slower methodologies or display output scanning that are not compatible with a motion type of POV display.

— bill