need help with a multi-input timer circuit.

Discussion in 'The Projects Forum' started by rollertoaster, Feb 23, 2008.

  1. rollertoaster

    Thread Starter New Member

    Feb 23, 2008
    4
    0
    This is my first post and I'm a NOOB at this. I understand the basics of how circuit components work but I have trouble putting it all together.

    My project is: I need a circuit that evaluates the voltages on up to 5 separate wires (each either 0 or 12v). When any or all of the voltages changes from either high or low I need a timer to trigger for about a 1/2 second to ground a relay.

    This project is for an automotive project so needs to be based off of 12v.
    I will be using it to monitor shift solenoids on an automatic transmission, and activate a relay during a shift for a period of about 1/2 second.

    any input would be greatly appreciated. Please dumb it down for me
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Perhaps you could make a five input AND gate from ten discreet diodes and trigger a 555 with the output.
     
  3. kraze_eye

    New Member

    Feb 24, 2008
    1
    0
    You need to tell us about how this is being inputed. Are there switches on the shifter already that you're tying into? Also you should look into a 555 timer that is setup to be a one shot (aka monostable mode)

    http://www.electronics-tutorials.com/devices/555.htm

    Further information about the inputs is key tho for us to help you get anywhere.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I'm just trying to ensure that I understand your situation correctly.

    You need to have the capability of generating a 1/2 second "ground pulse" if any of your (up to five) input wires changes from 0V to 12V, or from 12V to 0V.

    Is that correct?
     
  5. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    OK...I have not bench tested this (and I don't have a simulator), but I think this might work. Each of the 5 input XOR's form an edge detector with a positive output pulse whos width is determined by the 100k resistor and the 4.7uF cap...about 1/2 second. The 5 diodes form a 5-input OR driving paralleled XOR's to drive the transistor that pulls the relay to ground. Don't know what the relay is, so no spec on the bias resistor or transistor. The 10K resistors on the inputs are to keep the XOR gate inputs from floating, if there is time when the input is not 0v or 12v as with a Break-before-Make mechanical switch...but not necessary otherwise.

    Ken

    OK... I bench tested one XOR input, and it performed as expected.
     
  6. rollertoaster

    Thread Starter New Member

    Feb 23, 2008
    4
    0
    An edge detection circuit is exactly what I need I just didn't know the terminology. And the 5 input OR gate would work also, I was thinking of using a timer on the output of the OR gate but I would like to be able to fine tune the on time of the relay. What would determine the bias resistor? the impedance of the relay coil?

    I've been reading all of the technical manuals on this site for the last week and for the life of me I can't understand how alot of the circuits work. I understand the theory mostly, but when I look at the circuit it's like I'm trying to read chinese. I'm the kind of person that has to see it in action to understand.
     
  7. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    Here is another, but untested, circuit. Maybe I can bench test it tonight. Note that the XOR gates have been changed to XNORs and the diode directions have changed. I think the relay On-time can be varied from about 0.2 Sec to 2 Sec.

    Ken

    Bench tested and works OK!
    Still don't know anything about the relay so no spec's on R11/Q1. Relay coil resistance will determine how much current it uses, and point to the correct transistor and resistor.
     
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