Mixo bell problems
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  1. #1
    Fellow Frogger! badabec's Avatar
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    Default Mixo bell problems

    Hello, my DS20 ambulance came with nee-naw horn trumpets (no compressor) and a Mixo Cornevil ting-a-ling bell.
    The trumpets need a very large compressor to make them work so they have been abandoned for now.

    The Mixo bell has an electro-magnetic coil which propels a bullet shaped piston to hit the bell, ting. But I can't see any mechanism to keep the bell ringing. Door bells have a sprung metal strip that makes and breaks contact. With my Mixo, if you keep power connected, it goes ting and then the coil gets hot quite quickly. Not much good on a 999 (911?) call.

    I wondered if the power supply came from the points side of the coil and the running engine kept the bell ringing.

    The electro-magnetic coil is at an angle, gravity returns the piston to rest.

    Anyone any experience or ideas?

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    I was going to bin it until I saw the prices they ask so I'd like to get it working with the country horn (Strebel Nautilus).

    Thanks

    Peter

  2. #2
    Fellow Frogger! badabec's Avatar
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    Hello, can anyone in the brains trust suggest a way of providing a pulsing 12v supply to the bell? A relaxation oscillator is the fancy name, I just have no idea how to make one electro-mechanically. I don't think Citroen would have used fancy electronics.

    Any ideas?

    Would this work? When horn button is pressed, power goes to relay terminal 30, through contacts to bell via 87 and to relay terminal 85 energising coil. This opens the circuit, power is cut off, returns to original state, power is on again and so on. Uses a 5 blade cross over relay, one blade is not used.
    Attached Thumbnails Attached Thumbnails Mixo bell problems-mixo-bell-vibrator-1.jpg  
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    Last edited by badabec; 11th July 2018 at 08:38 AM. Reason: faffing about

  3. #3
    Tadpole
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    Default

    The idea will work, you will get a pulse train out of it, but I suspect it will not provide a satisfactory bell sound, and it's not easily tuneable to get different pulse rates or widths.
    The circuit here is much the same as an indicator circuit, so I'd try a indicator flasher relay. There are adjustable ones available, though most of the ones on the shelf these days are electronic.
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  4. #4
    BVH Roger Wilkinson's Avatar
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    robmac's your man. PM him if he doesn't respond here.

    Roger

  5. #5
    1000+ Posts robmac's Avatar
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    Default

    Quote Originally Posted by badabec View Post
    Hello, can anyone in the brains trust suggest a way of providing a pulsing 12v supply to the bell? A relaxation oscillator is the fancy name, I just have no idea how to make one electro-mechanically. I don't think Citroen would have used fancy electronics.

    Any ideas?

    Would this work? When horn button is pressed, power goes to relay terminal 30, through contacts to bell via 87 and to relay terminal 85 energising coil. This opens the circuit, power is cut off, returns to original state, power is on again and so on. Uses a 5 blade cross over relay, one blade is not used.
    The problem with the circuit you show will how the bell sounds. Essentially you will one have very short pulse powering the bell, it may not even have time to sound. You need a pulse train to keep the bell sounding.

    Mixo bell problems-msm.jpg

    The circuit you need is an astable multivibrator circuit. Essentially a square wave generator. You will be able to adjust the value of Ra and Rb to vary the cadence (sound) of the bell. I would suggest a mark/space of 1:1 and repetition rate of 2-5 seconds.

    A 555 timer is the no brainer way

    https://electrosome.com/astable-mult...tor-555-timer/

    Bells are a highly inductive load and create all kind spuggles, spikes and unwanted back EMF.

    You will need to switch the bell with relay powered from the 555 output. Make sure you put a quench diode across the relay coil.

    You will also need a noise filtering filter network the chip power supply.

    Best to get a friend with some electronics background to assist you. Parts will very cheap but some practical electronics skill will be needed to make it work.
    Last edited by robmac; 11th July 2018 at 02:45 PM.
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  6. #6
    Fellow Frogger! badabec's Avatar
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    Hello, plenty of 555 on eBay, then I saw an adjustable cyclical timer with relay for just over £5. As I'm ok with electrics but useless at electronics it seemed a bargain. Thanks Robmac for giving me a starting point.
    And it works.
    Country horn is now two normal horns plus Strebel Nautilus plus an old style police bell.
    Get out of my way!
    If only they would let me wire up the blue flashing beacon on the roof....

    Sent from my SM-J510FN using aussiefrogs mobile app

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