LED - analog dimming or flicker reduction

Thread Starter

Mark1964

Joined May 22, 2016
11
I have been working on a project that that has 8 strings of LED's (80ma per string), controlled via PWM from a Arduino.

For medical reasons I need to build a version where the LED's are controlled and dimmed from the Arduino but with no flickering.

I have done net search and am not really coming up much..

Any suggestions would be appreciated...

Regards
M
 

bertus

Joined Apr 5, 2008
22,094
Hello,

What PWM frequency are you using?
A higher PWM frequency will reduce / eliminate the flikkering.

Bertus
 

Thread Starter

Mark1964

Joined May 22, 2016
11
Thanks Bertus

The problem is the the frequency is adjusted via a light sensor..
I was thinking of using some sort of D to A filtering (low pass) but I am unsure how it would work with a variable frequency.

Mark
 

dannyf

Joined Sep 13, 2015
2,197
For medical reasons I need to build a version where the LED's are controlled and dimmed from the Arduino but with no flickering.
I can understand no flickering for medical reasons but what kind of medical reasons that would force you to build it with an arduino?

the arduino run their pwm at 400hz-ish, so unless you have some un-human eyes, it is tough to envision anyone being able to see flickering at that kind of frequencies.
 

Thread Starter

Mark1964

Joined May 22, 2016
11
And pins 5 and 6 as I understand have a peak frequency of approximately 980 Hz.

Modern CFL bulbs run at between 5 khz - 40 khz.

Certain forms of Epilepsy are aggravated even by modern CFL's.
We have an incandescent only policy in our home because of it.
 

dannyf

Joined Sep 13, 2015
2,197
We have an incandescent only policy in our home because of it.
wow.

well, if your medical condidition calls for the use of an arduino, and you need pwm in excess of 40khz, I guess you are out of luck then.

if you are willing to go by the arduino, three options:
1) use a faster chip. plenty of them out there;
2) change the prescaler. this potentially allows you to run at 62KHz or even 2x of that.
3) use analog lighting controls.
 

Thread Starter

Mark1964

Joined May 22, 2016
11
It's interesting how Consultants Increase epileptic activity in patients under scan by shinning high frequency LED torches in their eyes..
I guess some of us are just analogue people...

Everything is built with the Arduino, it does all the floating point maths etc.
I guess the bit I am stuck on is can the Arduino be used in any way for analog control and the best way to go about it.
 

dannyf

Joined Sep 13, 2015
2,197
It's interesting how Consultants Increase epileptic activity in patients under scan by shinning high frequency LED torches in their eyes..
yeah, but how high is that "high frequency"? probably nowhere near 500/1Khz. that would be in the superman territory, :)

can the Arduino be used in any way for analog control and the best way to go about it.
Obviously it can. Arduino can easily output an analog (voltage), and a voltage-controlled CCS (to drive the leds in analog fashion) is easy to build.

whether it is optimal depends on your objective and constraints you have to live with.
 

Thread Starter

Mark1964

Joined May 22, 2016
11
I think it's pretty high, I must find out.

The only real constraint Danny is reliability.

I am going to have a crack at this implementation of an LM358

 

dannyf

Joined Sep 13, 2015
2,197
at this implementation of an LM358
the pick of a lm358 for this application is pretty good.

otherwise, you need a slight change to the topology, a power resistor, and a power bjt or a power mosfet to get it done. Lots of heat sinks too.

with that said, i think you are far better off first confirming that 500/1Khz isn't a problem for you -> it is unlikely a problem for 99.99% of the people out there. Even fewer if you were to change the prescaler settings.

You are forcing yourself into solving a non-existent a problem, I think.
 

Thread Starter

Mark1964

Joined May 22, 2016
11
Ok Danny, thanks for your help and I appreciate your opinion.
I will look into the pre scaler settings and leave the circuit as is for now.

Regards
Mark
 
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