LED at half brightness [HELP]

Using Arduino LEDs and Multiplexing
1

Hey, I'm making an arduino car for my programming exam. The car has two LED's on the front, who I only want to give half power. I'm going to use an analogWrite, and in the loop, I'm gonna set the analogWrite value of the LED's to 125 (since a LED's range is from 0-250).

My problem is; I want to give the LED 125 as a Value (which is half of its capacity), BUT, the analogWrite "spectrum" goes from 0 - 1023. So if i Write 125 as the analogWrite value, the result is really low...

If anyone understand my problem, please help me with the converting... :slight_smile:

2

You've got analogWrite which takes 0 to 255 confused with analogRead that gives 0 to 1023. If you want half power write analogWrite(127). Note that half power and half brightness might well be 2 separate things. To get the latter you may need to play around with the values a bit.

3

So, I want the LED to have only half *Brightness (my bad) but if I write 127 in analogWrite, nothing happens becouse even though 127 is about the half of 255, 127 is just a little bigger than a tenth of 1023, so that doesnt work :S

4

What the he'll does 1023 have to do with it? Nothing. That's the max for READING analog values. 255 is full on for WRITING analog. If you want 50% duty cycle PWM then that is 127.

5

Oh, I understand now :slight_smile: But, when I write 127 as the value og analogWrite

ex:

analogWrite( frontLed1, 127);

It won't light... But, if I take it to 255 or higher, it will.

6

What Arduino are you using? And how is the LED wired?

7

Im using Arduino Mega 2560.

The LED is wired like this:

short pin to breadboard -> 220 recistor from the same line as short pin, to minus (on the plus/minus lines on the breadboard). -> minus from breadboard to ground on arduino.

long pin from LED to digitalPin 30 on the Arduino.

Fml... I have to wire it to an analogpin on the Arduino right?...

8

You have to write to an analog OUTPUT. Not one of the analog inputs. It will be,one of the digital pins with the little ~ symbol next to it. If you try to call analogWrite on a pin that doesn't support PWM then anything 127 or less writes LOW and anything 128 or higher writes HIGH.

9

On a MEGA that means pins 2 through 13 or 44 through 46. 30 doesn't support PWM.

10

Hahah, im just really tired... Changed the pins and everything worked perfectly, thanks alot :slight_smile: didn't think of that, only had to PWM pins left to use so didn't see it haha :slight_smile: Oh, i didn't know 44-46 was PWM aswell, thats nice. Thanks alot for the help :slight_smile:

11

But how do I make it blink for only 20 seconds when i turn one way, using millis()?