pwm to voltage with rc filter

Discussion in 'General Electronics Chat' started by alirezajafari, Aug 12, 2015.

  1. alirezajafari

    Thread Starter New Member

    Jul 1, 2015
    i have a sensor that the output of the sensor(TSOP 1138) is pwm with frequency 38KHz , i wanted to convert it to voltage
    because i used low-pass RC filter that the value of the capacitor was 1uf and the resistor was 100Kohm but i don't have a good response time
    i got mixed up perfectly
    what should i do???:eek:
    would you mind helping me that i can find the best value of the capacitor and resistor for that RC filter?:(
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    Welcome to AAC!
    What response time do you want? How much ripple can you tolerate on the DC? Time constant = R x C, so for 1uF and 100k = 0.1 sec.
  3. MrAl

    Well-Known Member

    Jun 17, 2014

    Yes it is a trade off between good filtering (low ripple) and fast response. The longer the time constant the better the filtering but the response time is then longer. There are other filters that might help that use other techniques for getting faster response and smooth output, but there is always some ripple so you have to decide how much is acceptable and how fast it really needs to be.
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    What are you using to read this IR sensor..
    What are you doing with it that you need to convert the PWM?
    You need to read the pulses to determine the remote codes not flatten it out.
  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    Since the most accurate way to measure the information contained in a PWM signal is to measure the pulse itself I have to ask what is making the measurement?