motorhome alarm

Discussion in 'The Projects Forum' started by plumber1969, May 10, 2011.

  1. plumber1969

    Thread Starter New Member

    May 9, 2011
    16
    0
    Hello im a newbie

    Im new to electronics and keen to learn

    I plan to wire up a 16 paking sensor around the side skirts of my motorhome
    As the sensor starts to detect the contol box send a variable votage to the buzzer at stage 1 to 3 of detection 1 to 6volts {which has two wires positive and negative coming from the control box }

    I want to remove the buzzer and wire this into a relay that will allow a 12 volt battery to power about 10 small lights

    what type of relay should i use ? to trigger the coi at 1voltl

    I was thinking connecting the four more wires to the buzzer cable so i have two feeds one to the relay and one to a siren

    At stage 4 of detection the voltage changes to about 10.78 volts
    I what to be able to connect the trigger wire of a voice activating siren to come on.You can approach the sensor and the siren will come on at stage 4 but chirp as ithe sensor go through the detection of stage 1 to 3 also when you move away the variable voltage interupts it and triggers it off again

    Is there something i can wire between the buzzer wire and trigger wire that will only allow say 10 volts through so the siren will only go off at stage 4.

    Also if you approach the sensors to quickly the siren wont come on so maybe add a relay as well only to come on or at say 10 volts

    again what type of relay should i use to trigger at 10 volts

    I have search the net but cant find anything suitable within the range i need.




    thankyou
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    Welcome to the AAC forum.

    Just a word to the wise - you'll get more responses if you take the time to spell-check and write as clearly as you can.

    If I understand your request, you're looking for a way to take the signals from the output of your sensor controller, as input into the circuit you're asking for, and have that circuit control a graduated response. Lights on at 1v, also chirping?, siren on at 10v. I couldn't quite follow what the voltage levels are and what is supposed to happen at each level.

    There are several ways to accomplish this. My approach would be a comparator such as the quad LM339. Each of the 4 comparators on that device could be set to turn "on" at the appropriate voltage level, giving you 4 levels of response.

    Each of the 4 outputs of the comparator can drive a MOSFET as a switch, behaving much like a relay. Depending on the current required, you may not need any mechanical relays since the MOSFET can easily switch 5A or so without any special heat sinking. If you need higher currents, the MOSFET can drive a relay coil.

    There are also specialized comparators that can be used as, for instance, as a bargraph voltmeter. It has maybe 10 levels to indicate the input voltage.
     
  3. plumber1969

    Thread Starter New Member

    May 9, 2011
    16
    0
    Thankyou wayneh

    Reading my post again and trying to clearly say what im doing is difficult I will try again.

    The detection stage of the sensors is

    stage 1 150-100cm bi...bi...bi
    stage 2 90-50cm bi..bi..bi
    stage 3 40-30cm bi.bi.bi
    stage 4 0-20cm bi...........

    At stage one of detection the contol box sends a live signal to the buzzer and the buzzer makes a noise .i have measured this signal and it is a variable voltage between 1 and 6volts .I would like to remove the buzzer and use that same wire but use the signal from it to either power a relay to allow 12 volts to power 10 led lights

    I would like to have these lights flashing at the same signal rate from the buzzer wire . flashing quicker as someone get closer. the buzzer would normally sound quicker as you get closer to the sensor from stage 1 to 3

    At stage 4 of detection the buzzer makes at constant noise.which i have check on the muiltmeter and this is a constant live of 10.78

    Its at this stage when i would like the siren to be triggered.

    There are only two wires coming out of the control box to the buzzer one live and one negative .So I think I may need to supply two separately feeds from the buzzer wire so one goes to the siren and one goes to the lights Then deal with the voltage deferences to trigger them separately .

    I have read what you said about the comparator and using MOSFET as a switch thankyou will read up on these .

    Forgive my ignorance,

    There are two voltages from the buzzer wire ie stage 1 to 3 and stage 4

    Im having trouble with the siren coming on too soon i only want this to come on at stage 4 .The problem is the sensor will turn on the siren at stage 1 to 3 or as you move away from the sensor 3 to 1.
    so i thought that i may need something to only allow 10 volts through the wire to trigger the siren so the siren does not pick up the other voltages and come on.

    Thankyou again
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    OK, it's much clearer now, thanks. Unfortunately it's also more complex than I first thought.

    First question: Is the buzzer simple and "self-contained", needing only a DC voltage to produce a tone, or is it receiving a tone from the controller? That would be an AC signal and a little trickier.

    Second question: It seems to me that the controller is sending the same signal out to the buzzer, varying only the amount of time the signal is on and off - the duty cycle. The DC voltage you measure may just reflect the duty cycle, with the meter not fast enough to show the separate on and off voltages. Possible?

    The good news is, it should be easy to make the lighting behave the way you want. You won't even need the comparator. Just feed the signal to the gate of a MOSFET, and that will allow switching plenty of current for your LEDs.

    A circuit to sound the horn when the controller is sending a continuous tone is trickier and maybe someone here has an idea. I think it will require a 555 timer circuit. I'm thinking the timing could be set to hold the siren off unless no reset (low voltage) is received for a certain time. We'll need to be sure what sort of signal is coming out of the controller.
     
  5. plumber1969

    Thread Starter New Member

    May 9, 2011
    16
    0
    Thanks that was a quick reply

    The buzzer is a self contained unit that plugs into the control box.

    I have taken the buzzer connector out of the control box and put my multimeter on the two pins testing the voltage at the different stages of detection.

    I would say it is a self contained buzzer needing a dc voltage to produce a tone.

    Thankyou
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    OK, well let's see if we can get the lighting part up and working as easily as I think we can. Do you have any MOSFETs? If not, you'll need one (or more, allowing for oops). I have a handful of IRF540 that would be fine for this, but there are MANY other options out there. I think Radio Shack offers something, maybe IRF510, and that would also work fine. Basically, you need an N-channel MOSFET with a current capacity at least ~4X higher than your expected lighting current.

    Pay attention to the pins of the MOSFET - it's easy and common to switch them up. That's true for beginner and pro alike. he only difference is that the pro knows to check and recheck and always assume it's been done wrong until you can prove otherwise. The beginner hopes for the best, and - Murphy's Law - often gets the worst. The Source pin of the MOSFET gets attached to ground, and the Gate receives the signal from your controller box. The Source now connects to the lowest voltage point of your lighting circuit. The MOSFET will control current flow on/off by opening and closing the path to ground. Voltage at the gate will open the path.

    Your lighting circuit should already work fine when connected directly to your power supply, without the MOSFET. If you need help creating the LED circuit, let us know. For testing you might want to just try any 12v light bulb you might have.

    If your controller is doing what I think it is, you should see the light coming on in sync with the buzzer.
     
  7. plumber1969

    Thread Starter New Member

    May 9, 2011
    16
    0
    Thankyou very much wayneh

    This is very helpful if it is not too much trouble i would really appreicate help with a drawing of this circuit and the leds

    I have been on youtube learning more about the mosfet and have learn`t about the gate /drain /and source as you say.

    With regards to the siren to stop it coming on at stage 1 to 3 or 1 to 6 volts can i put a 10 volt linear voltage regulator to only allow 10 volts through to trigger the siren .

    Thankyou
     
  8. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    You said you want ~10 lights powered from a 12v battery. Will this also see higher system voltages, eg. 16v when the ignition is on and charging the battery? Do you already have the lights, and any specs for them?

    No, the regulator can only drop (never raise) the voltage from a higher source, down to the stated voltage. If the input is lower, the output will be whatever the input is, minus a couple volts.

    I'll try to make time to sketch out a MOSFET control circuit, unless someone else wants to beat me to it.
     
  9. plumber1969

    Thread Starter New Member

    May 9, 2011
    16
    0
    Thanyou wayne i have ask the supplier via email for the wattage of the led

    These will only be powered by a 12 volts supply from the car battery as you say when the car battery is turn on and charging by the alternator it will increase.Ithink to around 14 to 15 max


    With the voltage regulator i may have confused you again .

    The supply of voltage to the buzzer at stage 1 to 3 is around 1 to 6 volts

    at stage 4 it is 11.78

    To have just the siren coming on if i put a voltage regulator of 9 volts on this circuit will this prevent the 1 to 6 volts turning on the siren at stage 1 to 3of detection.

    Will this only allow 9 volts through now to trigger the alarm .

    The alarm does not need 11.78 volts to be triggered i just wanted it to come on at this stage of detection.

    Thankyou
     
  10. plumber1969

    Thread Starter New Member

    May 9, 2011
    16
    0
    I have just got the email back from the supplier and each led draws less that 1 watt so the total for the leds will be a max of 10 watts

    Thankyou again
     
  11. plumber1969

    Thread Starter New Member

    May 9, 2011
    16
    0
    Hello

    Well i have wired it all up like a ring main circuit this time and it works better .However i dont have enough power to the leds.But the siren seems to work ok? The only other problem now though is i accidently connected the live from the battery to the buzzer wire and now the sensor just detects all the time the is a live of 7 volts constant from the control box so i assume some componant has blown.I have linked two images can you tell me where to place the mosfet to have more power for the leds.and if possible what componant would you think would have blown?

    http://postimage.org/image/t3iivl0/

    http://postimage.org/image/51kv6jus/


    Thankyou
     
    Last edited: May 11, 2011
  12. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    That's bad news. Your controller is most likely blown, and is quite complex. You might start a separate thread on this forum to see if anyone is skilled enough to advise you.

    I'll draw out the MOSFET switch, but now you've got a bigger problem.
     
  13. plumber1969

    Thread Starter New Member

    May 9, 2011
    16
    0
    Thanks wayneh

    You have been very helpful.

    The joy`s of experiments.I`m hoping to fix it other wise its back to the shop for another one.

    I will try another thread first

    Thankyou
     
  14. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    OK, well here's what I was talking about for using the controller and a MOSFET to control however big a load you want.
    Picture 1.png
    One big advantage of this approach is that there is almost no load on the controller. In your first circuit above, the controller is directly driving all the LEDs. That might be fine, but if you don't know the controller specs for driving an output, it might overload.

    The details of each string of LEDs will depend on your specific LEDs. The idea is to use as many in each leg as you can, while maintaining the brightness you want. Use a small ohms resistor to limit current, too much of which will ruin your LEDs. You really need to know the current specification.

    Using system voltage, as show, is a problem because it varies. With the circuit I've shown, you need to design for the highest voltage or else you'll fry the LEDs. When voltage falls to just the battery, the LEDs will dim. I think that's probably fine for most application, but you could include a 7812 regulator to avoid this problem. Then you could up the brightness at 12v and know the LEDs are protected from anything higher.
     
  15. plumber1969

    Thread Starter New Member

    May 9, 2011
    16
    0
    Thankyou Wayneh


    You have been extremely helpful and have given me a good head start with my project.


    Thankyou
     
Loading...