Drive an LM3914 from PWM

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi,

I am trying to drive the input signal of an LM3914 from PWM, however the PWM is causing this to flash the LED set from min to max (imperceptibly so it looks like they are always at max). I would like to use the full rage of v (0-5v). Any suggestions on a capacitor type and value to use to smooth a PWM v5 (0.45v step value) or v1.5 (0.15v step) output so that the LM3914 would see a smooth or steady ish v? I also assume the capacitor would be connected from +sig to ground.

Thanks

2

the PWM is causing this to flash the LED set from min to max

Yes that is what PWM does.

Read:-
http://www.thebox.myzen.co.uk/Tutorial/PWM.html

3

I understand the digital to analogue question, what drivers could you recommend for 20 LEDs? I can't get an LM2698 in a DIL package and I am not sure what other options there are.

4

Ok I see Charlieplexing is the way I should go. :slight_smile: Thanks for the input.

5

This desire to light many leds is most often solved by using Shift registers.