Custom dash wiring - indicators?

Discussion in 'Automotive Electronics' started by martyn jones, Jul 11, 2017.

  1. martyn jones

    Thread Starter New Member

    Jul 11, 2017
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    I'm working on a 1970 mustang race car and it needs to pass the MOT here - I've wired some buttons on a steering wheel switch panel that will control lights, turn signals, horn etc - there is no original dash and it will be a custom job. I've got push to make latching switches for the indicators and that's my issue at the moment. I've set it up on the bench with a supply and it's working fine apart from the fact that I can push both buttons together and it will flash both sides at the same time (one flasher unit) - I'm guessing i need momentary switches with latching relays, but how do i make them independent from each other? also how do i wire the same switch to break the circuit so I can turn off the indicators. Does that make sense?
    Thanks for your help
     
  2. BR-549

    Distinguished Member

    Sep 22, 2013
    2,865
    671
    Not much. Are you trying to move all your switches from steering wheel to custom made dash?

    Are you taking about your left and right hand turn signals........and your 4 way emergency?
     
  3. geekoftheweek

    Member

    Oct 6, 2013
    90
    11
    Something I did in a S10 once after I found out the turn signal wires in the steering column were melted... Use a dpdt switch for each left and right turn. Make sure it's a two position switch and not one with a center off position.

    Run your wire from your flasher to the NO terminals of the switch. Run your wire from your brake light switch to the NC terminal of the half of the switch going to your rear lights. Run one wire from the common terminal of one half of the switch to your rear light, and the other common to the front light and dash indicator.

    You'll have properly working brake lights and turn signals!! As long as your flasher is rated for the number of bulbs your 4 way flashers will work right also. If you want I'll toss together a drawing tomorrow night.
     
  4. martyn jones

    Thread Starter New Member

    Jul 11, 2017
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    It's taken me a month to remember where I posted this lol. That'll teach me for not bookmarking. Anyway - my turn signal switches are separate right and left buttons on the left and right side of the wheel. I'd like them to latch and unlatch from the same button, but they'd have to be exclusive - that is When right is on and left is pushed then right gets turned off and left goes on. When right is on and right is pushed again then it goes off. Same goes for the other side. Does that make sense?
    Thanks for the replies.
     
  5. martyn jones

    Thread Starter New Member

    Jul 11, 2017
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    Is it possible to use a flip-flop circuit actuated from a single push to momentary switch that controls a relay for each side of the turn signal wiring? Also somehow run the turn signal switch so it turns the flip-flop of the other side off only if it is flipped?
    In a real world scenario:
    Driving and wanting to turn left: Press LH momentary switch and it latches the LH relay to flash the LH signal
    Want to turn right straight after so press RH button which unlatches LH relay and latches RH.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    Here's my take on a circuit with flip-flops to control the turn-signal relays.
    The LTspice simulation is below:
    Notice that a turn signal is canceled by pushing either the same or the opposite push-button.
    R1, C1, and R5, C3 are to prevent spurious response from the mechanical contact bounce of the push-buttons.
    There are two flip-flops in one CD4013 package.
    The circuitry inside the dotted lines on the left is just to simulate the pressing of the PB's, and X1 is a dummy connection for the simulation.

    upload_2017-8-12_12-8-30.png
     
    Last edited: Aug 12, 2017
  7. martyn jones

    Thread Starter New Member

    Jul 11, 2017
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    That looks exactly what I'm after. Could drive the relays straight from the Q outputs of the flip flops?
     
  8. crutschow

    Expert

    Mar 14, 2008
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    Only if you have a relay that can operate on a mA or so of current.
    Those flip-flops can drive just a small amount of current, thus the need for the transistor to drive the relay.
     
  9. martyn jones

    Thread Starter New Member

    Jul 11, 2017
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    Ah ok, gotcha. I'll rig it up on a test bench. Cheers again!
     
  10. crutschow

    Expert

    Mar 14, 2008
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    There is one other consideration and that is the power up initial condition.
    If you remove power to the circuit when the engine is off, then it may power up with either one or both the signals on.
    The easiest is just to leave power applied to the flipflop (you can remove power to the transistors) since it takes only microamps of current.
    Otherwise you will have add circuitry to insure that the flipflop comes up with the turn signals off when power is applied.

    Also note that the power and ground connections are not shown for the flipflop which must be connected.
     
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