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Thread: 555 Timer Problem.. Need it To Trigger when key removed

  1. #11
    Raw Wave shotgunefx's Avatar
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    Quote Originally Posted by fire
    im expecting it to both toggle on and off the inverter..
    so on when the key is in... and off 30 seconds after the key is removed..





    yup i require high to low... siince when triggered it shorts it to ground?..
    now.. are u saying connect ACC to pin 2 on the 555 timer (the trigger input)..
    it will give 12v when the car is on.. and nothing when the car is off.... does this mean i need to disconect that 10k ohm resistor that connects 12v line to the trigger (pin 2)...
    now when ACC is off... will it start timing.. or will i need to somehow ground pin 2 at that point of time?


    i never realised a carputer could be so fustrating...
    im only 18.. and VERY new to electronics.. so bare with me



    EDIT: i dont have keysense.. i would love it for so many things.. but my subaru doesnt have it.
    also.. interesting read on the 555 timer
    (BTW, I'm no expert either, so take my advice with a grain of salt and don't blame me for anything )

    See that's where you lose me. Don't see how you can do that with one monostable, not with that circuit anyway.

    When you pull the trigger low, the output goes high for the time specified and then it goes low again.

    So when the car starts, the trigger and reset go high, so the output should be low (sinking)

    If the relay is grounded to the output, then the relay will close when you turn the key.

    Now when you turn off the car, it triggers the pulse which makes the output go high (sourcing current), meaning the output and battery + will have the same potential (or almost anyway), so no current flows, which means the relay clamps off. addition: so after your 30 seconds, the relay comes back on!

    If the relay isn't grounded to the output, but is being driven by it (meaning one side of coil is at output, one at ground), then what should happen is, the car starts, the trigger is high, the output is low and the relay doesn't open at all until you remove ACC.

  2. #12
    Low Bitrate fire's Avatar
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    ill check that out in the morning..
    if it doesnt work.. ill draw up a diagram so you guys can see what ive done exactly..

  3. #13
    Low Bitrate fire's Avatar
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    Question

    ok.. i tried connecting the trigger and output in many ways.. no luck..
    i connected the output as a ground like said.. it didnt change the input trigger and the inverter will be off if the key is in...
    i also tried to connect ACC to pin 2.. the trigger.. (i removed the resistor and relay circuit).. and no luck.. nothing even triggered the thing to start counting...




    find attached the original circuit that i wired up (my drawing schematic):


    like i said:... it works only if i turn the key on.. and straight back off again..
    the inverter stays on untill the timer has finished counting its 30 or so seconds:


    what should i change / modify to get it to work like i want?
    any chance you could draw it up on my circuit?
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  4. #14
    Maximum Bitrate pRoFiT's Avatar
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    Quote Originally Posted by shotgunefx
    Or just get a PIC
    Yah i was going to say that for the first reply but thought i would see what happens first.

    If you can program a pic chip that would be the fastest way to do it. A pic chip with internal timing. A LM7805 for 5Volts power, a transistor and some resistors to control the relays and away you go. Probably take an hour to program and build.

    edit: And there are tons of schematics on how to build a programmer for it.
    Um, I guess this is where you put something witty.WITTY

    My Web site, in the design stage. http://home.comcast.net/~cstrachn

    Modified RRSkinEditor http://www.mp3car.com/vbulletin/rr-skins/65723-rrskineditor-bugs-fixes-comments-current-progress-outdated.html

  5. #15
    Low Bitrate fire's Avatar
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    hmm.. sounds complicated.
    surely theres a way around it without a PIC??..:|

    if not: could you point me in the right direction by giving me the model number of the PIC i would need?
    ive been looking and found this: PIC16C84... i believe from the datasheet it has a timing feature... but damn.. i wouldnt even know where to start :|...

  6. #16
    Raw Wave shotgunefx's Avatar
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    Quote Originally Posted by fire
    hmm.. sounds complicated.
    surely theres a way around it without a PIC??..:|

    if not: could you point me in the right direction by giving me the model number of the PIC i would need?
    ive been looking and found this: PIC16C84... i believe from the datasheet it has a timing feature... but damn.. i wouldnt even know where to start :|...
    PICs aren't that complicated. I mean, there's a learning curve, but something like this is easy. Any 16F* or 16C* would do it.

    An 18pin would be fine, get one with a builtin oscillator, then you only need to flip a bit and use a resistor for the timer, or wire it straight to ground and get 10mhz without worrying about crystals and resonators.

    I normally don't use Assembler for programming PICs, the asm isn't that difficult, very simple actually as ASM goes, but I prefer C, so if it were me, I'd get on supported by the free version of HITECH C (I know they support 16F627,16F628, and many others). Mostly I've used 16F627,16F628 and 16F877As.

    You also need a programmer, I'd get a Olimex PGC-1 or PGC-2, cheap, can be had for ~ $15. Another benefit, with a little work, a MAX232 and some caps, you can interface the PIC from your PC.

    Or you could do what I did originally when I didn't know when to start, pick up a cheap protoboard like this one.

    http://www.sparkfun.com/commerce/pro...products_id=17

    For under $20 bucks and a PIC, your hardware (outside of a transistor for the relay) is done. It's got a serial port, a MAX232 with caps, serial port connector, 20mhz timer and a ICSP header (ie: you can program it in circuit)

    The also have those cheap programmers too.
    http://www.sparkfun.com/commerce/cat....php?cPath=1_6

    But back to your circuit...

    When ACC turns on, Relay1 closes, pulling down the trigger and starting the timer, which isn't what you want. (Also, you need to read the section I pointed out about driving inductive loads, and using a diode or you get timing glitches, also need quenching diodes on the relay coils, same thing if your using PICs)

    You want the trigger to get pulled down when the car goes off, but then you need to turn it on too.

    Ignoring the startup part for the moment, what seems to me is that you'd want the trigger hooked directly to ACC, Relay1 I don't think is really needed. The trigger has a pretty high input impedence, > 2M ohms, so that's only (12V / 2,000,000 ohms = 0.000006 amps), not much of a drain on the battery.

    But how do you get it to start? That's the rub, I suppose one way would be to just use two relays, one driven by ACC to operate the inverter (while the trigger is high), another driven by the 555.

    Though relays take some time to close (maybe up to 100milliseconds, not exactly sure), so you might get a power glitch as one relay is opening, and one closes.

    But this is why I like PICs, as soon as you need to change something, it's a matter or changing a 2, to a 5 or whatever

    A book that I thought was pretty good on PICs was "Programming Robotic Controllers" by Myke Predko

  7. #17
    Low Bitrate fire's Avatar
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    thanks for that detailed post..
    ill go to a electronics specialist today and get a few little parts and venture into PIC's..

    yup i did read your initial post about inductive loads.. ive been mucking around with diodes.. they are connected at the moment but not soldered...that circuit is my initial circuit i wanted to start with...


    hmmm i like your last statement...
    ill try 2 seperate circuits:
    A relay Straight off ACC+ to turn on the inverter.. with a largish capacitor to hold the relay open for half a second or something, which would give time for the timer circuit to activate....

  8. #18
    Low Bitrate fire's Avatar
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    Ok.. after lots of fiddeling and researching.. I have finally worked it out!!

    My idea was to scrap the 555 timer, and just work with a capacitor and resistor to hold open a relay.. i found out that i would need a HUGE capacitor to hold the relay open for long enough.. with a 4700uF.. it only stays on for 0.5 seconds...


    so i was wondering if i could encorporate a transistor.. i read about MOSFETs because i knew they have low power consumption.. i tried for hours wiring it up.. and came up with the circuit i drew below..
    i used a program called TINA v7... their website has a demo that you can use but you cant save.. so i just print screened..


    The 12 volt line connects directly to the Relay coil, and the relays ground is given by the transitor, when it has been activated by the ACC.. When ACC is removed, the capacitor should have charged, and therefore held open by the capacitors charge..... it works for around 45 seconds... if i lower the resistance or capacitor i will get less time.. if you want more time.. increase the size of the capacitor or the resistor....

    the idea of that push button is to discharge the capacitor quickly and the timer stops!.


    it has worked flawlessly testing it.. and i have put it in the car.. works so well..it doesnt even get warm.. i put a heat sink on the transitor because it had the hole and i had the heatsink.. so why not...

    If you have any questions.. please ask...
    Thanks to all those who helped me through this ....

    note to shotgunefx:... ve learnt.. ive now put diodes on all my relays to stop that glitch... thanks!
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  9. #19
    Low Bitrate fire's Avatar
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    Heres a Part List:

    C1 = 220uF Capacitor
    R1 = 135k Ohm Resistor, 1/4 Watt
    R2 = 1k Ohm... 1/2 Watt.. but i think 1W would be better.
    D1 = Any Diode really. there isnt much current, so doesnt need to pass much.
    MOSFET transistor: IRF520, BS170, or 2N7000... its a NPN transitor with a GATE, DRAIN, and SOURCE.... i think lots would work?
    a Push Button (momentary, for instant off)
    a 12v Relay



    note:.. i know that the circit from the switch of the relay is just a closed loop i just drew it like that...for me it connects the inverter..everone would have their own application i guess.

  10. #20
    Raw Wave shotgunefx's Avatar
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    Glad you got it worked out.

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