PWM to LED bar

Discussion in 'General Electronics Chat' started by Bärman, Nov 15, 2012.

  1. Bärman

    Thread Starter New Member

    Nov 14, 2012
    I'm about to design a circuit that will convert a PWM signal to a bar with 20 LED's. The PWM signal is locked to 300hz and 12Vpp with an offset at 12v. The signal is also inverted (100% duty when the level is at 0V.)

    I want a LED bar with the resolution of 20 LED's to represent the duty cycle. I.E 50% equals 10 LED to be lit and 60% would result in 12 LED.. and so on.

    My first thought is to use a second order low pass filter and a LM3914N (dot/bar display driver) but i have some trouble finding out which components and values to use.

    I'm from Sweden but I hope I made my self understandable.
    Thank you in advance!
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
    I agree with that approach. A simple L-C filter will convert the pulse train into it's DC value (which is proportional to duty cycle). To fine tune component values, build it on a proto board. At 300 Hz, you won't have any problems using a flying leads breadboard.

    That makes it more complicated, you will have to invert that if you want the LED string to read proportional to input duty cycle.