As far as I know, duty to voltage converters are simply low-pass filters.
In your case cut-off frequency of the filter is very near to the pulse
carrier frequency. To filter 15 Hz out of signal with an LP filter  with 10
Hz cut-off frequency you will need very high order filter - Is it realistic?
Why simply not use interrupts on edges of the PWM signal and read timer
value at these moments? It takes only about 20 instructions to convert timer
samples  to the pulse width. With constant PWM frequency you can use look-up
table to convert pulse width to analog value.
I used the same approach to read output of Analog Devices TMP03 temperature
sensor - It has floating frequency of 20-40 Hz and needs about 120 kHz
sampling rate to get accurate measurement. Worst of all, it needs both pulse
width and period measurement :)

Cheers
Nikolai

-----Original Message-----
From: Jon Petty <Phxsys3@AOL.COM>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Monday, November 01, 1999 11:12 PM
Subject: 0-100 duty cycle at 15 Hz to a 0-5v analog


>Hi
>
>I am looking for a circuit that will convert a 0-100 duty cycle at 15 Hz to
a
>0-5v analog signal to send to the ad converter. 50% duty= 2.5v. There are
>some timing reasons why I don't want to measure the pulses directly. The
>analog voltage still needs to be responsive with a refresh rate of at least
>10Hz, so a large cap (1000 uF)  makes the response to slow. I found lots of
>circuits for converting voltage to a variable duty cycle or frequency to
>voltage, but nothing for duty to voltage.
>
>Any ideas or suggestions?
>
>The simplier the better.
>
>Thanks
>
>Jon
>
>