LED dimmer module - ideas wanted

[lesthegrngo]

Hi All

I have a number of panels that are LED backlit, mostly 12v DC powered. The problem is that they are quite variable in their brightness, and so I would like to have a simple module for each one that allows me to regulate them individually to match. I was thinking maybe a small PCB with something like a PWM controller and a trim pot, and found this

https://www.circuits-diy.com/led-dimmer-circuit-with-555-timer/

It looks simple enough, except that the 'picture' doesn't show the extra diodes and capacitors. The questions I therefore have are:

are the extra components there to compensate for the fact that the input voltage on the schematic is shown as 5 - 18v? Bear in mind my input will be a stable 12v

I will be using it with up to 50 surface mount 0805 LEDs ranged in banks of four, would the MOSFET still be required? I was hoping some kind of surface mount device could be used instead for packaging reasons

Is there any reason why the potentiometer can't be replaced by a small SMD trimmer pot? Ditto the resistors and diodes, assuming I can get suitable ones

Cheers

 

Les

 

 

[No1sonuk]

The components on the left provide the timing and duty cycle adjustment. 

I don't remember what pin 5 does.

The MOSFET is required to drive the LED current.  The 555 output couldn't do that itself.

All the parts can be surface mount. Just keep an eye on the LED current draw and MOSFET rating.

If you have a spare Arduino, you could use it with the inbuilt PWM outputs to provide software control of a few LED MOSFETs from one device.

Edited June 16, 2023 by No1sonuk

[lesthegrngo]

Thanks

I saw an arduino controlled dimmer while looking at the various circuits. It's tempting, but at least at the moment I'll keep it simple. One other question, the way this would dim is by a square wave, right, rather than a sinusoidal wave. That means that the LED's will strobe, I just want to check whether it would be intrusive, as I know peripheral vision is more sensitive to it

Les

[No1sonuk]

It needs to be square to work.

PWM works by turning on at full power for the whole cycle, or part of the cycle. So on full cycle = 100% brightness. On 50% of the cycle for 50% brightness. Sine waves won't do that.

Whether or not it flickers is down to the frequency.  If the switching frequency is in the audible range, you might hear it "whine" as well.

Avoid frequencies that are exact multiples of your room lighting AC power, too.

As for keeping it simple: I've not used a 555 since I learned how to program a PIC...

Edited June 16, 2023 by No1sonuk

[lesthegrngo]

Are there any workable alternatives to the PWM method? Not sure I like the idea of the whining sound

Cheers

Les

[No1sonuk]

Use a frequency above your hearing range...

The only thing you can do is try it.

Real aircraft AC power systems usually run at 400Hz. That gets annoying after a while!

One of the phrases we use at work when people comment on how loud the airliner ovens we're fixing are is:

"If you can hear that in a flight, you have bigger problems because the engines have stopped!"

The upshot is that even if it does whine, you might not be able to hear it over the other noises.

Or you could set the frequency at 400Hz and make it a feature.

Edited June 16, 2023 by No1sonuk

[bnepethomas]

I've used the PWM pins on a Arduino, works well.  Good dimming range with no obvious flickers
https://github.com/bnepethomas/bne-arduino-flight-simulator-interfaces/tree/547932be65f759cf038e3f2a632a62336e5e0f8f/PCBs/OH - Hornet Forward Upper Output Shield

I take the output directly from DCS BIOS

https://github.com/bnepethomas/bne-arduino-flight-simulator-interfaces/blob/547932be65f759cf038e3f2a632a62336e5e0f8f/DCS BIOS Sketches/Active/UIP_MAX7219_NEXTRON_POWER_RELAY/UIP_MAX7219_NEXTRON_POWER_RELAY.ino

 

 

Edited June 18, 2023 by bnepethomas

[Vinc_Vega]

That's what I did too.

Taking the console lights signal from DCS and sending it to a PWM pin to control the backlight via MOSFET.

Different light levels may be adjusted or calibrated within the Arduino code of the respective panel.

Regards, Vinc