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Thread: [resolved] timed relay.... keeping voltage when origional connection broken....

  1. #1
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    Exclamation [resolved] timed relay.... keeping voltage when origional connection broken....

    hi guys...

    i am located in the uk, so if suggesting places to buy what i need please bear this in mind.

    i am hooking up a cheap alarm system to my car doors.. [if doors open when central locking locked siren goes off - for say five mins...

    i achieve this by grounding the siren power....

    so. i can do a simple If door opens then door circuit grounds. however, this means siren stops if door is closed. no good if a fast robber....

    i need a way, that if it grounds, it stay grounded until i break the coil power wire [second ground connection on remote central locking - when locked]

    basically,

    siren positive = battery poss...
    siren neg = grounded via some relay... = loud noise
    for said relay to be able to ground, it needs to ground via remote central lockin "starter kill" ground [in my case i have built in immobiliser, since i just bought a newish car - so this grounding point is now free]

    so door opens, relay will ground via door circuit... and open the grounding for siren, door closes, relay stays open... until rcl is unlocked, [relay power ground on second relay maybe?] or a timed delay is reached...


    im sure somebody has done something simular before... so if possible... :P i was thinking of getting a light dimmer, which fades out the light, but this would last say 30 seconds or so...

    if someone got links etc..

    thnks in advanced.

  2. #2
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    Quote Originally Posted by wayneox View Post
    hi guys...

    i am located in the uk, so if suggesting places to buy what i need please bear this in mind.

    i am hooking up a cheap alarm system to my car doors.. [if doors open when central locking locked siren goes off - for say five mins...

    i achieve this by grounding the siren power....

    so. i can do a simple If door opens then door circuit grounds. however, this means siren stops if door is closed. no good if a fast robber....

    i need a way, that if it grounds, it stay grounded until i break the coil power wire [second ground connection on remote central locking - when locked]

    basically,

    siren positive = battery poss...
    siren neg = grounded via some relay... = loud noise
    for said relay to be able to ground, it needs to ground via remote central lockin "starter kill" ground [in my case i have built in immobiliser, since i just bought a newish car - so this grounding point is now free]

    so door opens, relay will ground via door circuit... and open the grounding for siren, door closes, relay stays open... until rcl is unlocked, [relay power ground on second relay maybe?] or a timed delay is reached...


    im sure somebody has done something simular before... so if possible... :P i was thinking of getting a light dimmer, which fades out the light, but this would last say 30 seconds or so...

    if someone got links etc..

    thnks in advanced.
    i think i had an idea, so lets see if i cant get it across lol. run power from your power to pin 30 on your relay, and from pin 30 run to the anode side of an SCR (silicone-controlled rectifier), then from the cathode side of an SCR to your 85 pin on your relay, hook 86 to ground, 87 to your horn and then ground. connect the gate of the SCR to your doors so that when they open they supply a power source to teh battery. heres my fun times schematic lol (apologies


    batt ----------------30 87--------horn-----ground
    | +++++++++++++++ |
    --------door circut--SCR
    +++++++++++++++++|
    +++++++++++++++++85~86--------ground


    (+ are just filling space to format)

    i realise the door circut here is not as you currently have it set up, however all you need is a momentary pulse of power to get it "latched" open, and i cant imagine why you couldnt just hook em up to a power source (a 12v battery might even work actually, pending on the SCR lol).

    if theres some sort of timer you could put in, put it, as well as any on/off switch, between the SCR and pin 85. so that way it will function again if someone opens another door, and if you turn it off, you wont have to worry about sounding the alarm lol. im sure theres something wrong with this diagram, or i have my anode and cathode backwards (it was over a year ago and we spent maybe a day on em ok? and i hate transistors :P)

    also, want to make sure the power supplied isnt going to fry the SCR, or go over the breakover voltage.

    for more information, this is what i used as a quick reference: http://www.allaboutcircuits.com/vol_3/chpt_7/5.html

    and remember, the simpliest circut is the best

    the floor is once again open *phew*

  3. #3
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    Quote Originally Posted by gaoes View Post

    batt ----------------30 87--------horn-----ground
    | +++++++++++++++ |
    --------door circut--SCR
    +++++++++++++++++|
    +++++++++++++++++85~86--------ground

    hey cheers for that... never heard of SCR before... but google is my friend i know.

    i basically had this idea, forgot to post it... i know how i want it to work, hopefully others can see what is happening... but im not sure if everything i need is available or needed... or even works how i expect it to lol... sorry for the reception class drawing :P



    basically black box is latching relay, open and close coil have hot positive connections
    as does siren, and a open close relay.

    trick is to latch them via a short grounding...

    so central locking locks, providing a ground [or unlocks providing ground, not sure which is which but its a matter of switching two wires on the five pin relay ]

    so its locked - providing ground, then a momentary relay [i believe i can use this to send a pulse for a short time to the latching relay] is armed, so if door opens, the ground is made, and the ground connection - via initial relay - is sent to latching relay... door closes, latching relay has already latched open...so siren keeps going... [till the battery dies or unlocked]

    so unlocked, siren is sounding... the initial relay is to closed position, it then i asume i need a momentary relay again??? with the source being ground, and coil ground to the initial relay, to send a ground pulse to the close / off coil of the latching relay

    am i correct in this thinking? if so, parts list:
    standard five pin relay *1
    4 pin momentary relay * 2
    latching relay *1

    for now i just want to arm the siren and disarm it, but if somebody could help with the time issue great.

    i read something about storing charge in a capacitor to power a relay coil, which draws power from battery, not sure how that works exactly though.... basically works like an interior light dimming switch, but it keeps the full power till capacitor is fully discharged, since power is actually coming from battery, and only cuts when coil isnt magnetised enough to hold the connection. - taking a stab at this. im assuming... a very low voltage relay, opening a second relay for siren, when second relay closes another third momentary relay sends a pulse to close the siren relay... - for this to work the capacitor would need to power via the door cicuit correct?... - what ive read so far assumes i actually know anything about circuits - which i dont lol

    once again, thanks for your reply sir, and to everyone for lookin :P

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    Quote Originally Posted by gaoes View Post
    batt ----------------30 87--------horn-----ground
    | +++++++++++++++ |
    --------door circut--SCR
    +++++++++++++++++|
    +++++++++++++++++85~86--------ground

    ok i think i get this, but i just need to confirm

    my door circuit runs on a negative current... so do i need to connect it like this:


    or do i need to alter it so it keeps a negative... sorry totally new to circuits etc, if i have a good simple plan i can copy... im good, but new stuff :P lol

    i assume the relay is a must for this project, yes? so as not to burn out the SCR. - the SCR just keeps the relay coil live, yes?

    i can see lots of SCRs on ebay... is this the type i need?
    http://cgi.ebay.co.uk/S0402DH-Silico...item3a455c4448


    or do i do it like this...? - sorry not exactly sure but if so... can i wire the SCR to avoid the second relay to convert the door circuit to a positive pulse...?

  5. #5
    What can I say? I like serial. Curiosity's Avatar
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    How will someone get into the car if it's locked? Slim jim or break the glass? There are latching relays that work similar to the lock solenoids in your car, which take a forward or reverse pulse to lock and unlock. That might be an easier way to engage and disengage the circuit. You could also use a cheap alarm shock sensor as a trigger. They are 12V with a negative pulse similar to a door open.

  6. #6
    Raw Wave
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    Don't forget EPA or other requirements - eg, here a car alarm may not sound for 2 minutes.
    Then some triggers are not allowed to re-trigger (eg switches etc).

    I did have a simple circuit somewhere that I used (30 years ago!).

    And I have circuits to latch and break a normal relay, but that assumes +ve trigger - I'd have to convert for ground trigger....

  7. #7
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    Quote Originally Posted by Curiosity View Post
    How will someone get into the car if it's locked? Slim jim or break the glass? There are latching relays that work similar to the lock solenoids in your car, which take a forward or reverse pulse to lock and unlock. That might be an easier way to engage and disengage the circuit. You could also use a cheap alarm shock sensor as a trigger. They are 12V with a negative pulse similar to a door open.
    my car doesnt have deadlock.

    what i see is for someone to get at my stereo etc they need to open the door, central locking sends pulses if door latch is opened so all door opens... but even if doors are unlocked via cars system, the central locking brain remains locked unless unlocked via key...

    i also plan to purchase a shock sensor that will be incorperated so when locked the shock / ultra sonic sensor will be grounded & active and when the air is disrupted [window smashed etc] the siren will sound, via a pulse from sensor, which i will hook up same connection as the door circuit - but again this will be later.

    cheers.

  8. #8
    What can I say? I like serial. Curiosity's Avatar
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    You should get under the dash and find the BCM. Then grab a DMM and start poking around. Usually you can stick a probe in the back of the connector to make contact. Write down all the pins and volts or if no volts, if grounded and make note of any changes when armed/disarmed/locked/unlocked. Also google for alarm installs for your make/model. The DIY instructions can help with what wires do what. After that you might have some new ideas that will make it easier.

  9. #9
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    Quote Originally Posted by OldSpark View Post
    Don't forget EPA or other requirements - eg, here a car alarm may not sound for 2 minutes.
    Then some triggers are not allowed to re-trigger (eg switches etc).

    I did have a simple circuit somewhere that I used (30 years ago!).

    And I have circuits to latch and break a normal relay, but that assumes +ve trigger - I'd have to convert for ground trigger....
    ive wrote this twice now, so sorry if i forget something but...
    i will look at EPA ETC, not sure what they mean, but ok...

    but two min not sounding, would this be a delay? due to scr? or?

    as we no im no expert otherwise wouldnt be here, but i thought as soon as circuit opens it would automatically sound? then when ground is lost on relay 86 pole, the scr return to off position, so when armed again, the door opens and goes back to on? would be greatful of any info possible - cheers

    also been looking at a lot of car alarm circuits, i recon i could also get a cheap fiver payg fone and set it to speed dial me when the alarm sounds, using 555 timers and after say 30 seconds hang up again... thus eliminating need for the timed cut off, as if my alarm sounds, i would check WHY it was sounding... and disarm it myself.

    PAYG phones in uk are able to top up via a credit card type swipe card in shops, so phone could be hidden away, never touched, left plugged in on charge running off own battery when engine is not running. - simple phones have WEEKS of standby time. - i have an idea of how i would manage this part of an alarm. only problem would be if someone cut the live and negative wires to my central locking brain, but by that time, my phone should of been called already. - but again this is for later.

    basically phone part would be... a dual relay, when open, one side charges caps of a second 555 timer. first side holds down speed dial 2 to call me on my mobile [a seperate one, not the one in the car ] when the second 555 timer runs out of power, a momentary pulse is send connecting the hang up button of phone - would aim for 30 seconds, to save credit on phone - since this is the approximate time for my mobiles voicemail.

    5 every six months to keep phone active would be nothing. and could even use it for a cheap gprs internet on laptop. and only use contract 3g when needed.

    also ive cleaned up my second diagram a little, since i think this would be correct??? - cheers.

  10. #10
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    that last cleaned up picture looks like it should work. just wire your door switches in parallel to the relay, so any of em could give you the alarm.

    as for the EPA thing i think he ment it cant sound for more then two min. now theres two things to this circut, any control mechanisms need to cut power or ground to the realy that has the horn, anythin you want to happen as a result of the alarm needs to go on the same circut as the horn itself.

    checking out that SCR you linked earlier, will edit as needed.

    ok, it looks like thats a 4A, 400V. ought to work just fine. you only really need to pull enough current to energize the relay. dont have to worry about hitting the breakover voltage either lol. if you want to test it out, i'd just get 3 9v's and put em in series. i would hate to be the cause of frying something in your car, so please test first lol.

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