PWM to analog voltage

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi,

I'm trying to make a bar visualization using the PWM on arduino and the LM3914 chips. But when I connect the PWM output to signal input of 3914, it just keep flashing. I guess is the PWM doesn't really output analog voltage so the leds connected to the 3914 just keep blinking all the time.

Any idea to deal with this? I read something about using RC circuit to generate analog voltage, but I'm not sure how to do it, any idea?
Thanks~

Cheers,
Hamlet

2

There is an application note here http://ww1.microchip.com/downloads/en/AppNotes/00538c.pdf that describe the theory. Try connecting a 1k resistor from the PWM output to the input of the LM3914 with a capacitor across the input (from the LM3914 input pin to ground). You may need to experiment with various values but I would start with a value around .1uf to 1uf.

3

Thank you so much! Appreciate that, will post the test result when I figure it out~

4

Seems to be fine with the setting below
Resistor : 220Ohm * 5 (Don't have a 1K resistor in hand)
Capacitor: 0.47uF

Works quite well, just need to adjust the ref voltage now.

5

Good to hear its working. You can go up in resitor value if thats easier, anything up to 5k or so should work. The values are not critical.