thread: DIY Digital gear display

  1. #1
    Woodsport Paul Woods's Avatar
    Mar 2005
    Durham, UK birthplace of the 1.5,v6 and v8 Mr2
    14,617

    DIY Digital gear display

    On the Mk1 2gr 6 speed i made my own digital gear display, but it used far too many microswitches on the gearstick and didn't have the ability to display 6th or Neutral properly, so this time around i wanted to go one better.

    This is probably more easily achieveable with clever electronics based on RPM and Tach inputs, but i'm not clued up on microprocessors etc, so i have put a few hours into a switch and relay circuit that i think works, this time only using 4 switches instead of 6, but it does use 5 relays.

    The gear indicator unit i am using is a seven segment display but already prewired so that each wire grounds the segments needed to make a digit, so no need to use a 4 bit binary system (although that too may be possible with clever use of switches/relays)



    I think i've come up with a circuit that will ground each wire it needs to independantly of the others, and also displays neutral when none of the others are selected..... it has melted my brain but i am asking some of the more cleverererer electrical types among you to prove/disprove the logic of this circuit... ie, does it work. Some of the polarities on the relays might be wrong but ignore that for now, if you study the diagram you will see what i am trying to achieve.

    Also i welcome any comments to simplify the circuit using less relays or switches.




    This unit is going to be mounted in the centre of the Evora cluster in the unused automatic gear display area.
    Last edited by Paul Woods; 27-03-2016 at 18:06.

    TB Quote of the month:"I split my ear open whilst masturbating" - Jasper Full story Here

  2. #2
    Woodsport Paul Woods's Avatar
    Mar 2005
    Durham, UK birthplace of the 1.5,v6 and v8 Mr2
    14,617
    3rd gear relay is wrong..... i need to correct that, bollox!

    TB Quote of the month:"I split my ear open whilst masturbating" - Jasper Full story Here

  3. #3
    Grenade's Avatar
    Dec 2012
    Cleveland Ohio USA
    2,027
    Holy sheep shit batman- my brain melted just reading that!

  4. #4
    jimi's Avatar
    Feb 2006
    Kingdom of Fife
    435
    Need more info on how the switches operate in relation to gear selection.
    Assuming (which I hate doing) that the drawing shows the switches in the Neutral state (and you have use normal electrical convention for the relay states) then all the relays except for the Neutral relay are energised which means your earthing 2nd, 6th and N, which I'm guessing is not what you intended ?
    Jimi
    Black is not a colour ! .... Its the absence of colour

  5. #5
    Woodsport Paul Woods's Avatar
    Mar 2005
    Durham, UK birthplace of the 1.5,v6 and v8 Mr2
    14,617
    Yeah sorry Jimi i haven't had time to correct the polarity, but basically the left and right relays provide the ground path for the 1/2 , 5/6 relays which are then pulled to output each individual gear, if you study that part it works, but my 3rd gear relay is wrong.

    TB Quote of the month:"I split my ear open whilst masturbating" - Jasper Full story Here

  6. #6
    Woodsport Paul Woods's Avatar
    Mar 2005
    Durham, UK birthplace of the 1.5,v6 and v8 Mr2
    14,617
    In other words, a relay may be energised, but doesn't necessarily have a ground path through it, do you see that?

    Switch the output polarity on the left/right relays

    TB Quote of the month:"I split my ear open whilst masturbating" - Jasper Full story Here

  7. #7
    jimi's Avatar
    Feb 2006
    Kingdom of Fife
    435
    Normal convention on electrical drawings is to show everything in it's de-energised (no power) state. Same with the switches (hence my "in neutral" assumption)
    So looking (for example) at relay 1st/2nd. The relay is energised because of the contacts on the Forward switch, which means the relay contacts have changed state giving an earth return to 2nd gear display via the Far left gate switch. yes ?
    If you haven't used the standard electrical conventions then it will be difficult for me to work out whether the logic is correct because I don't know how you have drawn it. Would also help to understand the logic if I knew which switches are activated in each gear ?
    Apologies if you already know all this, just trying to understand how you intend it to work.
    Jimi
    Black is not a colour ! .... Its the absence of colour

  8. #8
    Woodsport Paul Woods's Avatar
    Mar 2005
    Durham, UK birthplace of the 1.5,v6 and v8 Mr2
    14,617
    I see what you mean, currently it only makes sense to me.

    I will do a logic flowchart or something to explain operation.

    TB Quote of the month:"I split my ear open whilst masturbating" - Jasper Full story Here

  9. #9
    jimi's Avatar
    Feb 2006
    Kingdom of Fife
    435
    I see what you mean, currently it only makes sense to me.

    I will do a logic flowchart or something to explain operation.
    Spot on :thumbsup:
    Jimi
    Black is not a colour ! .... Its the absence of colour

  10. #10
    Woodsport Paul Woods's Avatar
    Mar 2005
    Durham, UK birthplace of the 1.5,v6 and v8 Mr2
    14,617
    Ok Jimi, i have revised the diagram with the switches and relays in their powered off positions, hopefully now it makes sense..... i will also do a flow chart or something.

    I quite enjoy the challenge of getting a logic circuit to perform with simple relays and switches, it's like an early computer lol.


    TB Quote of the month:"I split my ear open whilst masturbating" - Jasper Full story Here

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