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Car project geting spike from the car electrical circuit

Discussion in 'Automotive Electronics' started by Turbo Boss, Aug 24, 2003.

  1. Turbo Boss

    Turbo Boss New Member

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    I am using a circuit in my car that include some CMOS logic gates and 555 timers.
    I know this chips work OK within 3 to 15 Volts.

    The projects work perfectly in my bench with a 12 volt battery BUT when I conect it with the battery from the car it work ok until I actvate a switch in the car like the door lock.

    Its look like my project is getting some type of spike or glitch from the car electrical circuit.

    What I have to do in order to fix this??? Do I have to install some kind of debounce circuit???

    Do I have to install a Voltage Regulator???

    Can somebody give me detailed instrucctions or point me to a wep page were I can find more info about this or a circuit that I can copy.

    Thank you for your time and help.
     
  2. nettron1000

    nettron1000 New Member

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    TB , thats not much info to go on.

    You mentioned you have logic gates and 555 timers, do you maybe have a schematic we can have a look at ?
     
  3. Turbo Boss

    Turbo Boss New Member

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    Well, I dont have a diagram. But is a CMOS INVERTER with a CMOS AND gate and a monostable 555. Is work perfectly on the bench with a 12 volts battery but in the car it get gliches or spikes from the electrical car circuits.
    Do you think I have to put some type of Regulator so it work with 5 volts?
    Do this will help????
     
  4. dave

    Dave New Member

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  5. nettron1000

    nettron1000 New Member

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    Yes adding a voltage regulator and proper filtering would be a good idea and should solve your problem. The electrical system in a vehicle is a very noisy invironment for electronics.


    BTW, the voltage from your car will be about 13.8 volts when it is running, so it would prolly be better to use a 9 volt regulator such as a 7809.
     
  6. ChrisP

    ChrisP New Member

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    Two good points!

    Consider the fact that the example you gave -- operating the door locks -- uses fairly strong magnetic devices. Now consider the fact that all critical on-board electronics are somewhat "hardened" for reliability and you should see a definite need for regulation, filtering, and shielding!
     
  7. stevez

    stevez Active Member

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    I was getting a lot of noise on a mobile radio based on observations from other hams and went to work on a solution. I put a scope on the cigarette lighter power supply and noticed tons of electrical stuff - including these incredible spikes. The timing of the spikes suggested that the most likely source was the fuel injectors. There was a lot of noise from the alternator too - that I eventually discovered must have been a failed diode. The spikes were very high in amplitude but of very short duration - an RF choke actually took care of the spikes - a capacitor helped and replacement of the alternator improved things as well.

    I guess autos are incredibly noisy and as a result automotive electronics is designed/tested with this in mind. To me that suggests that I'd try to do what I could to filter noise and also to avoid adding my own electronics to critical systems - that might fail at a bad time.
     
  8. Turbo Boss

    Turbo Boss New Member

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    I will going to use this schematic I find......... I going to regulated to 5 volts and on the regulated output I going to install a electrolitic cap 2,200uF/35V...... What you people think?? http://www.eleinmec.com/figures/020_02.gif

    Also what is the best way to shield my project? Is that a material that I use to cover the project. Do I stick that material to the inside part of the project box?

    THX
     

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