Page 1 of 2 12 LastLast
Results 1 to 10 of 20

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

  1. #1
    Low Bitrate fire's Avatar
    Join Date
    Oct 2005
    Location
    Melbourne, Australia
    Posts
    95

    Lightbulb 555 Timer Problem.. Need it To Trigger when key removed

    hello all ,


    Here's the senario.. I have a CARPC setup using an inverter which has a switch that i have re-wired to a 555 timer circuit that i made...

    Basically.. my idea is...
    the computer turns off when the key is removed.. (fake UPS tricks it into thinking its out of battery and begins hibernating).. this takes usually 10 seconds.. and sometimes as long as 16 seconds.. so i thought id make a timer to CUT the inverter after 30 seconds so my battery stays fine.

    now.. it all works perfectly when u trigger the timer to start counting (when it receives 12 volts from the ACC+ line).. however if you have the car on for longer then the timer period (30 seconds).. as soon as the key is removed it cuts the circuit and doesnt give time for a normal shutdown.


    My dilema is:
    i need something to either pulse +12v only when the key is switched off..
    or somehow modify the timer so it beggins counting when 12 volts is removed from it..........

    Heres where i got the idea for the timer..

    http://www.eleinmec.com/article.asp?4

    And this is the circuit i used:


    Here is how the timer is triggered according to that circuit:


    see how it starts timing on the leading edge.. i need it to start on the falling edge?.. any ideas??



    thanks alot!
    Tony.

  2. #2
    Raw Wave shotgunefx's Avatar
    Join Date
    Apr 2005
    Location
    Boston, MA
    Posts
    1,800
    Never had that much luck with 555 circuits, but if you want a pulse for when the car goes off, think about a cap.

    The cap charges and then acts like an open circuit, when the power is removed, it can drain through the trigger input.

    The problem I see is that it's going to hit the trigger twice.

  3. #3
    Low Bitrate
    Join Date
    Jun 2006
    Posts
    98
    This second circuit should work fine for you...

    Schematics/Pin Outs/Diagrams

    '98 Peugeot 306
    Project Status: I sold it ages ago!

    ShutControl

    The ultimate shutdown control software for laptops.

  4. #4
    Raw Wave shotgunefx's Avatar
    Join Date
    Apr 2005
    Location
    Boston, MA
    Posts
    1,800
    Hmm, let me rethink that.

    The 555 is triggered when the input goes low correct? If that's the case and you've got it wired to ACC, how is it triggering before the car is turned off? I'm assuming the 555 isn't running off the ACC line

    What is the output connected to? Can you give some more details?

  5. #5
    Raw Wave shotgunefx's Avatar
    Join Date
    Apr 2005
    Location
    Boston, MA
    Posts
    1,800
    Quote Originally Posted by blessani
    This second circuit should work fine for you...

    Schematics/Pin Outs/Diagrams
    Shouldn't there be quenching diodes on those?

  6. #6
    Low Bitrate fire's Avatar
    Join Date
    Oct 2005
    Location
    Melbourne, Australia
    Posts
    95
    ok... ive had a look at using a seperate cap.. but this double pulse stuffs up the system... i need a single pulse somehow only when the car is being turned off or else the timer already has began its counting.

    sorry for the lack in details..

    ok..ive used a relay for the trigger... (the coil is connected to acceccories and ground)... and the switch acts as the trigger as demonstrated in the circuit.,. only when accesories has power..... [sorry if this confused you into thinking i was giving it a high not a low..]

    The timer's power source is directly off the battery +12v and ground..
    and its output +12v triggers a relay to close the circuit for the inverter to be on (thus switching on the inverter)..






    this circuit im using is known as a 555 monostable circuit...

  7. #7
    Raw Wave shotgunefx's Avatar
    Join Date
    Apr 2005
    Location
    Boston, MA
    Posts
    1,800
    Quote Originally Posted by fire
    ok... ive had a look at using a seperate cap.. but this double pulse stuffs up the system... i need a single pulse somehow only when the car is being turned off or else the timer already has began its counting.

    sorry for the lack in details..

    ok..ive used a relay for the trigger... (the coil is connected to acceccories and ground)... and the switch acts as the trigger as demonstrated in the circuit.,. only when accesories has power..... [sorry if this confused you into thinking i was giving it a high not a low..]

    The timer's power source is directly off the battery +12v and ground..
    and its output +12v triggers a relay to close the circuit for the inverter to be on (thus switching on the inverter)..



    this circuit im using is known as a 555 monostable circuit...
    I'm a bit familar with the 555, but it's been awhile. A couple points for clarification.

    Are you powering the relay that drives the inverter from two circuits or are you somehow expecting it to both toggle on and off the inverter via the status of ACC?

    BTW another good 555 page.

    http://www.kpsec.freeuk.com/555timer.htm

    Note this...
    Like all ICs, the 555 and 556 must be protected from the brief high voltage 'spike' produced when an inductive load such as a relay coil is switched off. The standard protection diode must be connected 'backwards' across the the relay coil as shown in the diagram.

    However, the 555 and 556 require an extra diode connected in series with the coil to ensure that a small 'glitch' cannot be fed back into the IC. Without this extra diode monostable circuits may re-trigger themselves as the coil is switched off! The coil current passes through the extra diode so it must be a 1N4001 or similar rectifier diode capable of passing the current, a signal diode such as a 1N4148 is usually not suitable.

  8. #8
    Fusion Brain Creator 2k1Toaster's Avatar
    Join Date
    Mar 2006
    Location
    Colorado, but Canadian!
    Posts
    10,049
    Well it is soooo simple you probably overlooked it.

    Depending whether or not the trigger is set from the high-to-low pulse, or the low-to-high pulse, just take the ign line and NOT gate it or feed directly. It doesn't need a pulse, it relies on the high/low or low/high. So if you continuosly feed it IGN, then it goes from 0 at start to 1 all the way until you shut it off, then the 1-0 stage will trigger. I think this is the stage you want. High to low. If you want low to high, then just NOT gate the thing to ~IGN, and you have 1 at beginning, 0 until you shut it off, and then the 0-1 stage triggers.

    Now this will work to switch when the power is cut to the car. If you want to be able to kill your car, and leave your key in, then I suggest using your KEYSENSE wire to activate it instead of the IGN. I know some cars' keysense wire is data, not regular 0/12 so you need to get an immobilizer bypass of sorts to convert the data pulses into 0/12
    Fusion Brain Version 6 Released!
    1.9in x 2.9in -- 47mm x 73mm
    30 Digital Outputs -- Directly drive a relay
    15 Analogue Inputs -- Read sensors like temperature, light, distance, acceleration, and more
    Buy now in the MP3Car.com Store

  9. #9
    Raw Wave shotgunefx's Avatar
    Join Date
    Apr 2005
    Location
    Boston, MA
    Posts
    1,800
    Quote Originally Posted by 2k1Toaster
    Well it is soooo simple you probably overlooked it.

    Depending whether or not the trigger is set from the high-to-low pulse, or the low-to-high pulse, just take the ign line and NOT gate it or feed directly. It doesn't need a pulse, it relies on the high/low or low/high. So if you continuosly feed it IGN, then it goes from 0 at start to 1 all the way until you shut it off, then the 1-0 stage will trigger. I think this is the stage you want. High to low. If you want low to high, then just NOT gate the thing to ~IGN, and you have 1 at beginning, 0 until you shut it off, and then the 0-1 stage triggers.

    Now this will work to switch when the power is cut to the car. If you want to be able to kill your car, and leave your key in, then I suggest using your KEYSENSE wire to activate it instead of the IGN. I know some cars' keysense wire is data, not regular 0/12 so you need to get an immobilizer bypass of sorts to convert the data pulses into 0/12
    Or just get a PIC

  10. #10
    Low Bitrate fire's Avatar
    Join Date
    Oct 2005
    Location
    Melbourne, Australia
    Posts
    95
    Are you powering the relay that drives the inverter from two circuits or are you somehow expecting it to both toggle on and off the inverter via the status of ACC?
    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..



    Depending whether or not the trigger is set from the high-to-low pulse, or the low-to-high pulse, just take the ign line and NOT gate it or feed directly. It doesn't need a pulse, it relies on the high/low or low/high. So if you continuosly feed it IGN, then it goes from 0 at start to 1 all the way until you shut it off, then the 1-0 stage will trigger. I think this is the stage you want. High to low. If you want low to high, then just NOT gate the thing to ~IGN, and you have 1 at beginning, 0 until you shut it off, and then the 0-1 stage triggers.
    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

Page 1 of 2 12 LastLast

Similar Threads

  1. Not your typical flicker problem
    By JPuma in forum LCD/Display
    Replies: 17
    Last Post: 05-30-2007, 10:28 AM
  2. had an all day (9 hr) problem at work....
    By wizardPC in forum Off Topic
    Replies: 13
    Last Post: 10-20-2005, 12:50 PM
  3. NaviVoice v.6 RELEASED!
    By 0l33l in forum PowerVoice
    Replies: 28
    Last Post: 10-11-2004, 01:34 AM
  4. Delay power cut when key is removed.
    By Mastero in forum Power Supplies
    Replies: 11
    Last Post: 10-31-2001, 04:44 PM
  5. using a 555 timer to suspend
    By wizardPC in forum General Hardware Discussion
    Replies: 8
    Last Post: 12-27-2000, 01:58 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •