You have variable pulse positioning from timing marks unless you also vary the width of the strobe pulse at each compartment. While that's possible, it tends to blur the strobe image if too long and dim the image if too short if used instead of a optimized LED current for the strobe width.

From my simple POV demo of a single strobe LED. Top trace timing pulses, bottom trace time varying strobe pulses to timing mark.

Four strobe line demo.

I used this RGBA led with current limiting resistors to keep the peak forward current below the Max rating.
https://github.com/nsaspook/hd_pov/blob/xc8/ov4zrgba-1210202.pdf
https://github.com/nsaspook/hd_pov/tree/xc8

Is that your clock on youtube? I have seen that before. Mine is going to be a little different. I have numbers carved into a disk I made from plexiglass. Light shines through the numbers.

 

All right enough already. I get it. I am fully aware of the purpose of a current limiting resistor. I was just wondering if I might be able to get way without it in this case.

I'm not sure why you consider this is a special case. It sounds to me like every other situation with an LED needing something to limit current through it. If there is a good reason to treat this situation differently, I'd be interested in hearing it.

 

I'm not sure why you consider this is a special case. It sounds to me like every other situation with an LED needing something to limit current through it. If there is a good reason to treat this situation differently, I'd be interested in hearing it.

There are plenty of commercial products that don't have a specific component that limits the LED current. Instead, they rely on the near-ohmic V-I characteristic above the normal Vf and/or on the limited drive capability of the power supply. Probably the most common example are key-fob devices that put the LED directly across a coin cell, relying on the rather large effective series resistance of the cell to limit the current. So it's not unreasonable for someone to ask whether or not they can get away without a specific current limiting device in other situations. This just happens to be a situation where it is probably ill-advised to do so.

 

There are plenty of commercial products that don't have a specific component that limits the LED current. Instead, they rely on the near-ohmic V-I characteristic above the normal Vf and/or on the limited drive capability of the power supply. Probably the most common example are key-fob devices that put the LED directly across a coin cell, relying on the rather large effective series resistance of the cell to limit the current. So it's not unreasonable for someone to ask whether or not they can get away without a specific current limiting device in other situations. This just happens to be a situation where it is probably ill-advised to do so.

Fair enough. I didn't mean to make it sound unreasonable - just didn't see anything that made this particular situation seem safe without current limiting. My default would be to assume you always need deliberate current limiting unless you have a specific mechanism in mind that will limit the current for you. If you know some aspect of the circuit will intrinsically limit current, great. Otherwise, you've got to add something, right?

I'm aware of circuits relying on battery internal resistance. I didn't know there were deliberate uses of near-ohmic behavior of LEDs above normal Vf. I'd be interested in knowing more about that. I understand that they could stabilize at some current without going into complete runaway, but I'd have thought that current level would be unacceptably high based on all the LEDs I've known so far.

 

There are plenty of commercial products that don't have a specific component that limits the LED current. Instead, they rely on the near-ohmic V-I characteristic above the normal Vf and/or on the limited drive capability of the power supply. Probably the most common example are key-fob devices that put the LED directly across a coin cell, relying on the rather large effective series resistance of the cell to limit the current. So it's not unreasonable for someone to ask whether or not they can get away without a specific current limiting device in other situations. This just happens to be a situation where it is probably ill-advised to do so.

It is unreasonable, because he does not know about those methods. You(WBahn) on the other hand have the experience and thats why you suggest these methods. For him it was just a thought that occured, without knowing how the blocks of a circuit work and why(and thats why I call it the programmer's approach). Which is not offendind you(spinnaker), however these bad practices have to be stopped somehow.

 

It is unreasonable, because he does not know about those methods. You(WBahn) on the other hand have the experience and thats why you suggest these methods. For him it was just a thought that occured, without knowing how the blocks of a circuit work and why(and thats why I call it the programmer's approach). Which is not offendind you(spinnaker), however these bad practices have to be stopped somehow.

Again enough already. Stop turning this thread into an argument and finger pointing. WBahn please lock this thread. My question has been answered. My plan is to try and reduce the supply voltage to teh LED which was suggested and was a possible way to go that I had in mind all along.

 

Again enough already. Stop turning this thread into an argument and finger pointing. WBahn please lock this thread. My question has been answered. My plan is to try and reduce the supply voltage to teh LED which was suggested and was a possible way to go that I had in mind all along.

Sorry about that. I did not intended to turn it into finger poiting. There are just a lot of fatal mistakes in the appraoch taken today and we are all trying to change this. I do not mean anything bad by that.

 

Its only a fun project as clearly pointed out in the OP. If it burns up the LEDs it is no big deal.

 

Again enough already. Stop turning this thread into an argument and finger pointing. WBahn please lock this thread. My question has been answered. My plan is to try and reduce the supply voltage to teh LED which was suggested and was a possible way to go that I had in mind all along.

MOD NOTE: Thread locked at TS's request.