Negative Triggered JK Toggle - First (Working) Design, Critique Wanted

Discussion in 'The Projects Forum' started by Gareth Lowe, Feb 2, 2015.

Thread Status:
Not open for further replies.
  1. Gareth Lowe

    Thread Starter New Member

    Feb 2, 2015
    Gday from Australia Guys,

    First a little background, as an early teen, I was quite keen on Electronics, and although I built a few kits, never got any working, as I never really could , or perhaps did not try to grasp the concepts behind them when it came time to troubleshoot. A decade on older and wiser, I came back to building some Guitar FX, and although I still had no electronics knowledge, due to the craftsmanship skills I had honed, they actually worked, and sparked a renewed passion for the hobby again. I'm at the point now that I am really trying to get a handle on some of the basics, as I am a little bit beyond just being proud of having a working circuit, and as I learn best by doing, I decided to solve a problem that has been bugging me for a while.

    My car has a softlock feature, so if all the windows are down, and the sunroof is open etc, you can turn the key to a special position, and while you hold it there, it will wind everything / shut everything for you. A couple of years back with the help of my brother, we hooked this up so it could be operated by the remote, with a nasty hack at best that involves several off the shelf automotive relays, a cheap timer circuit, and a hell of a lot of crimps and black electrical tape. It works, but there is no reset pin to hit here, so if I ever lock the car, and then decide I have forgotten something, I just have to watch the windows wind up, and wait for the timer to time out at 30 secs. Believe me, I though I could get smart and grab my wallet while the window was going up just once, I ended up with my wrist trapped in the wound window for the full 30, much to the amusement of onlookers! I had no idea that those window motors were so powerful, I swear it nearly broke my wrist, and I ended up with some dark purple bruising for a good week.

    Anyway, so to fix the above, I have designed my first circuit with a 4027 JK Flip Flop, a 555, and a small handful of passives. I have set it up and tested it on a breadboard, and it seems to work great, but something in the back of my mind just tells me that I am missing a few components here and there, and that somethings going to burn out early, or jump out of state or something, so I was hoping some of the older hands here could take a look and give me a bit of critique.

    Heres the schematic


    This is my first attempt at laying out a schematic in Eagle as well, so do your worst ;)

    Now my rundown of operation is that I already have a tap to a negative trigger pulse coming from the remote immobilizer, which will trigger a state change in my 4027, giving my a toggle between lock and unlock. When Pin 1 is high it will provide VCC for the 555, and because Pin 2 is low, C1 can charge giving a short trigger pulse. When the trigger is again applied to the 4027, it reverses and sets Pin 2 High, which I will then use to trigger my Unlock relay, not shown, but in a similar transistor switch configuration to the one attached to the 555. This state switch also cancels the VCC to the 555, giving me that reset I have always wanted!

    Some of my questions are.. What does everyone think of the above configuration? Should I be regulating my 12v line coming from the Auto? Its already fused at 7.5A and only for the door lock switches. Where else is it pertinent to be putting some protection circuitry in this schematic? And are there any obvious ways I can simplify this. Like I said it works, but Im a big fan of elegance.

    Any input would be greatly appreciated guys, thanks all for your time in advance,

    Best Regards,
    Gareth Lowe
  2. MrChips


    Oct 2, 2009
    Hello Gareth,

    We appreciate that you took some effort to prepare your first post on All About Circuits. We will be happy to assist you with your electronics endeavors. Unfortunately this is one of them that stands against AAC rules.

    The owners of All About Circuits have elected not to allow discussions of automotive electrical system modifications/enhancements due to safety concerns, the potential of legal ramifications and the possible circumvention of vehicle regulations at the state and federal level.

    For this reason this thread is against the AAC forum rules, Chapter 6, as seen here:

    This can be found in our Terms of Service (ToS)

    Please do not bother to reword the question. It will not fly under the radar.

    Here is a site that may provide you with some assistance: Electro Tech Online

    You are very welcome to come back and discuss non-automotive electronics with us.
    Good luck.
Thread Status:
Not open for further replies.