Path: utzoo!yunexus!maccs!darel From: darel@maccs.McMaster.CA (Darel Mesher) Newsgroups: sci.electronics Subject: A Challenging PWM Design Problem Summary: PWM -> Analog Message-ID: <1663@maccs.McMaster.CA> Date: 5 Dec 88 18:44:23 GMT Article-I.D.: maccs.1663 Reply-To: darel@sparkles.UUCP (Darel Mesher) Distribution: rec.ham-radio, sci.electronics Organization: McMaster University, Hamilton, Ontario Lines: 65 I have an interesting Pulse Width Modulation design problem; Given the following PWM waveforms: Minimum pulse width: <----------------- 18 mS -------------------> .--. .--. ____| |________________________________________| |_____ --> <-- 1.0mS Maximum pulse width: <----------------- 18 mS -------------------> .----. .----. ____| |______________________________________| |___ --> <-- 1.9mS The pulse width varies linearly with a transducer variance of 0 - 100%. My question: is there a simple solution for the conversion of this PWM signal into a corresponding analog signal, ie. a simple circuit for the following black box? .----------. PWM in | | Analog out ------------>| |------------> | | `----------' where the analog output function looks like; Vcc | . | . | . | . | . | . |. -|-----------------, 1.0 1.9 Pulse Width (mSec) Obviously, if there exists a PWM De-modulator chip then this would be the answer, however I can find no such chip in any of my Linear data books. I currently have a solution using a oscillator, counter, and DAC however, the chip count is higher than optimum (ie. one :-) ). Any suggestions would be appreciated. Darel. -- Darel Mesher ...!uunet!mnetor!maccs!darel McMaster University darel@maccs.mcmaster.ca