Resistors and LEDs

[sharkfin61]

A question to all electronic affascinatos:

When I soldered my MAX 7219 board that came with the 8x8 red dot panel, I had to put in a 10k resistor.
After some time I brought my A-10 caution panel to life, however the lights were very weak.

--> Can I change the resistor to ine with a higher value  to gain more brightness on my 3mm green LEDs (3,2V  forward Voltage & 20mAmp)?

tyia

Edited May 12, 2024 by sharkfin61

[No1sonuk]

Do you have 1 LED per "segment"?
Generally speaking, a LOWER resistance would increase the current.

There's an interesting idea in post #6 here - use a pot to make it adjustable:
https://forum.arduino.cc/t/question-about-the-correct-resistor-for-max7219-rset/228971/7

Edited May 12, 2024 by No1sonuk

[Vinc_Vega]

The resistor is to limit the forward voltage and current, supplied from the Max7219 to ALL the LEDs. So you don't need any more resistors for each LED. Please read the documentation in the hardware part of the ledcontrol pages on how to select that one resistor (RSet). You still have to know the forward voltage and allowed current for your LEDs.

https://wayoda.github.io/LedControl/pages/hardware.html#SelectRSet

Edit:

According to the table you already should have 40mA output at 3V for each LED when using a 10kOhm resistor

Btw. the brightness of your LEDs even may be controlled by software. It's then easiest done with the ledcontrol library.

https://wayoda.github.io/LedControl/pages/software.html

 

Regards, Vinc

PS: Hey Joe, you also may PM me  

Edited May 12, 2024 by Vinc_Vega

[sharkfin61]

Thank you, @No1sonuk and @Vinc_Vega.

I have 1 led per caution field.

The intcity is alreadyset to:    lc.setIntencity (0,15); as per Craig's arduino sketch.

So I think, the brightness cant be set any higher, even with an additional potentiometer.

My suspicion was also, maybe the leds are the problem itself, because I used the ones with an internal resistor (datasheet attached). Lazy me 

 

@Vince_Vega PM Wilco (tomorrow).

Grüne LED CautPanel_Kingbright_L-934GD-5V.pdf

Edited May 12, 2024 by sharkfin61

[Vinc_Vega]

These are no typical LEDs as they already include a resistor for 5V applications. I think that they are for direct wiring to Arduino boards.

Maybe you have to interpolate the RSet to a Max7219 chip for 5V and 17mA from the data sheet. Than 10kOhm sounds plausible to me.

Your brightness should already be set to max from the software side: setIntensity(int addr, int intensity), where 15 is the max intensity value.

How is the brightness if you direct supply a LED from an Arduino with 5V compared to one at the Max-chip?

Best regards, Vinc

Edited May 12, 2024 by Vinc_Vega

[sharkfin61]

Zitat

vor 6 Stunden schrieb Vinc_Vega:

How is the brightness if you direct supply a LED from an Arduino with 5V compared to one at the Max-chip?

 

Will test that in the upcoming hours. Also, I'm planning to put some refecting metal tape and cover the inside of the stand-öff part (between the LED baseplate and the engraved sheet) of Romro Kilos caution panel design.

Edited May 13, 2024 by sharkfin61

[sharkfin61]

Well, it all came to a happy ending when I simply reduced the thickness of the spacer.
I'm glad, I made it from several  layers  of acrylic sheet and  didn't  glue it yet, so I just had the reduce it from 21 mm to 12mm. The brightness is now ok for me, just have to change 2 LEDs as it looks like  they went to LED hell.