PWM delay with Mosfet

Discussion in 'The Projects Forum' started by rfeyer, Mar 7, 2015.

  1. rfeyer

    Thread Starter Member

    Aug 24, 2014
    126
    0
    Hi all,
    since many of you have talked me through building a hen door opener/ closer with SPDT relays which allows concurrent lighting of a 12VDC light, I would like to add a feature of a time delay (motor has a 5 sec delay after 12VDC is received) as such:
    12VDC signal is sent to motor which draws average 1-3A, max 5A, but gets interrupted possibly with a 555 circuit, which allows a beeper to go off until 5 seconds elapse, then the current is allowed to continue to the motor.

    I thought I had this figured out with the below circuit until I realized: the 555 works the other way around: it allows flow for a time specified by R and C, then actually goes off on pin 3.
    Is it possible to work it how I need it - meaning, output to motor is delayed for 5 secs, then goes high?
    This is what I found online:
    upload_2015-3-7_9-36-46.png

    Rainer
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,998
    745
    What you have there is a motor speed controller, if you want a delay start, you need to hold pin 4 low for the duration of the delay, then make it high to run the motor.

    So adding a 1Meg ohm resistor on pin 4 to pin 8, and a 4.7uF cap from pin 4 to pin 1, will give approx 5 seconds delay .
     
    rfeyer likes this.
  3. rfeyer

    Thread Starter Member

    Aug 24, 2014
    126
    0
    TY UK!
    Before I start changing the schematic - I leave the current schematic as is and keep pin 3 as output?

    Rainer
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,998
    745
    yes,
     
  5. rfeyer

    Thread Starter Member

    Aug 24, 2014
    126
    0
    TY again!
     
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