A Simple Time Delay Circuit

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Introduction: A Simple Time Delay Circuit

About: Chemistry and electronics have been a staple in my life since I was 8 and have pretty much been my only hobbies although I have dabbled in herbalism, art, music, and various other areas as well.

I finally decided to add another line to my charge controller and I wanted a steady power output instead the PWM that comes off of the dump controller so I made this handy little circuit to take a PWM signal and change it to a constant DC signal.

Step 1: Gather the Materials

To build the basic circuit you will need:

  1. A MOSFET. I used an IRF3205
  2. A capacitor
  3. Two resistors
  4. Jumper wires

Step 2: Assemble the Circuit

Assemble the circuit according to the schematic.

Step 3: Testing and Tuning

Its now time to test the circuit and add the extras.

Add a button connecting the positive rail to the signal in line and connect an LED and a resistor to the signal out line. Apply power and push the button, if it lights up for a short time then fades out, the circuit is working properly and you can now add the relay if you do so choose. The way this circuit works is when the signal in, line goes high and charges up the capacitor and turns on the transistor. The resistor connected to ground slowly drains the capacitor of it's charge and when the capacitor reaches a certain voltage, the transistor fades out and shuts off. What the relay does is act as a type of quasi schmitt trigger and provides a nice transition from on to off without fading by breaking the contacts when the output from the transistor hits a certain voltage. This action would be handy for running electronic devices that can't really tolerate the in between voltages very well such as an induction motor driven pump (AC) or an inverter (DC).

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    7 Comments

    Can you take a picture about board without relay from upside?

    1 reply

    Well, I have since disassembled the circuit but I would be more than happy to answer any questions you have about it

    can you take a picture about board from upside?

    Awesome circuitry and very well explained.
    I believe you could also replace that relay with a comparator chip.
    Thanks for the post.

    3 replies

    Well, this is what I came up with. It works perfectly and I must say I like it better than the relay. I changed the resistor value going to the gate of Q1 to a 1K as well.

    time delay full.png

    IC1 should be LM741CS not LM318P. I just forgot to change the number.

    That would most definitely be a more robust solution. One thing I was
    thinking is using an op amp wired up as a comparator considering I have a
    few of those laying around. I'll include a picture. Most of my parts
    are harvested from other electronics including the MOSFET, capacitor,
    and relay used in this instructable so I kind of just use what I have on
    hand.

    op amp.png