Parking sensor

Discussion in 'The Projects Forum' started by plumber1969, May 11, 2011.

  1. plumber1969

    Thread Starter New Member

    May 9, 2011
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    Hello ,I have a parking sensor module.

    I accidently touch the wire that goes to the buzzer with a 12 volt live from a car battery .

    Now when I connect the buzzer wire to the module it makes a constant tone

    Before the tone would only come on as you approach the sensor and then as you got really close it would be a constant tone.

    The voltage that goes to the buzzer was 1 to 6 volts at stage 1 to 3 of detection and 11.78 at stage 4 of detection

    Now its 8 volts constant and when you get close goes to 4 volts

    I have attached a picture the 3 wires red,yellow and red with black are lives and neutral.

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

    The grey wire connects to the buzzer

    looking at the circuit board would there be anything obvious that might of blown?

    thankyou for any replies.
     
  2. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Just under the buzzer (probably a piezo osc) jack you will see a rectangular three terminal object. It looks like a transistor which you may have popped. Even if it is the blown component it's doubtful that you have the skill, experience or tools to replace it. This is a SMD board.
     
  3. #12

    Expert

    Nov 30, 2010
    16,261
    6,770
    I hope you are parking your lunch or your umbrella because if you're parking a car, this trhead will be closed.
     
  4. plumber1969

    Thread Starter New Member

    May 9, 2011
    16
    0

    I had the impression that this site was for intelligent people to discuss there electronic problems . <snip>

    Thankyou

    CDRIVE If you are referring to the LM7805 3-Terminal 1A Positive Voltage Regulator

    Then that is straight forward to replace

    Thankyou
     
    Last edited by a moderator: May 12, 2011
  5. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    I guess only you would know that. Blowing up the image only allowed me to identify R55, which is just below the device I mentioned. It looks like a transistor but SMDs can take many shapes. If it's a 7805 it should be easy to test. If it checks out OK then check the junctions (with power off) of the most likely transistors in the path of your errant voltage. I mentioned that component because it looks like it's connected to the sonalert jack.

    BTW, is this buzzer a self contained 'Sonalert', meaning it produces a tone like signal by applying DC to it? Sonalerts are basically Piezo elements with an integral oscillator built in. I ask this because if this is the case, I would expect there would be a transistor dedicated to switching the sonalert on and off and it would be the most likely candidate because it would be in the direct path of the sonalert jack.

    Keep in mind that trouble shooting via this medium requires a fair amount of guess work on the part of the respondents.
     
  6. plumber1969

    Thread Starter New Member

    May 9, 2011
    16
    0
    Hello C Drive

    Thankyou for replying that is very helpful.

    "BTW, is this buzzer a self contained 'Sonalert', meaning it produces a tone like signal by applying DC to it? Sonalerts are basically Piezo elements with an integral oscillator built in. I ask this because if this is the case, I would expect there would be a transistor dedicated to switching the sonalert on and off and it would be the most likely candidate because it would be in the direct path of the sonalert jack."

    It is just as you say the buzzer is powered by a dc current .The buzzer connects to the plastic plug which i have coloured with a pink marker

    You can just make out the little transistor in this link

    http://postimage.org/gallery/15u2s30h4/

    The number on it is WS A 78L08 92OSB

    I will test this as you say . I appreciate you can only go so far it just a point in the right direction im looking for.

    Its just a hobby i would like to get into and learn more of i can always take it to shop and get it fixed ,but that defeats why im hear trying to learn

    Thankyou
     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The 78L08 "transistor" is actually a fixed positive 8v regulator rated for up to 100mA output current, most frequently in a T0-92 plastic package.

    A datasheet is available here:
    http://www.national.com/ds/LM/LM78L05.pdf

    The "78Lxx" designation is an industry standard part number. Various manufacturers use different prefixes; National Semiconductor uses "LM" for many of their regulators.

    You should measure approximately 8v between the GND and OUT pins.
    For the TO-92 package, with the package oriented so that you can read the face, the center terminal is GND, and the left terminal is OUT, leaving the right terminal as the input.
     
  8. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    That should be an 8V regulator. Check it with power on to see if you're getting 8V on the output pin. I'm guessing that this is not what blew but check anyway.
     
  9. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    This is a snip from one of my posts. I emboldened the important parts. We're evidently not talking about the same component. I believe that I am and was quite clear. How did we get over to the other side of the board? The 78L08 is no where near that connector.
     
    Last edited: May 12, 2011
  10. plumber1969

    Thread Starter New Member

    May 9, 2011
    16
    0
    Thankyou again C Drive

    I have followed the guide for testing transistors.


    When i tested the very small transistor between the collector and emitter i did`t get OL i get a reading of 0.707

    I have since found this site http://www.eidusa.com/Electronics_Voltage_Regulator.htm

    The number on the transistor was LM7805 5D3 not as i said 503?

    I tested what you said and ground to in was 11.20 volts and ground to out was 5.52volts



    Thankyou again
     
  11. plumber1969

    Thread Starter New Member

    May 9, 2011
    16
    0
    Right to confirm

    I have tested the "voltage regulator " LM7805 which is to the bottom right of the picture about 10cm away from a blue resistor

    Then i have test a little transistor which is just in front of the votage regulator 78LO8 three terminal not as SgtWookie says?

    The jack plug to the buzzer is the second plastic socket in from the top right of the picture?

    Thankyou
     
  12. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Yes, and for the third time... the transistor in question is directly under it, just above R55.

    If we can agree that were talking about the same component then I will give you some pointers on testing it.
     
  13. plumber1969

    Thread Starter New Member

    May 9, 2011
    16
    0
    Thanks CDrive Right got there third time lucky then.


    Its a j3y very small i see where you were coming from now with regards to fixing it.As you said it will be to difficult to replace but i would still like to just check it.

    I need to add four of these control boxes together .Each box has 8 channel ports for 8 sensor but only 4 work at any one time as it is meant for working on a car ?As I want to use 16 sensors I will need to add four boxes together.

    Im using these parking sensors as a motorhome proximity alarm detector have now manage to wire up the 12 leds to the buzzer wire with the help of wayneh wich now works and the leds mimicks the pulse of the buzzer at the different detection ranges and a voice siren then starts all working fine.All off one control box with 4 sensors

    The problem is that i have discovered by blowing one up if i connect another 12 volt source to the buzzer wire it damages the unit.

    Each buzzer wire for each control box gives out a 10.78 volt at stage 4 of detection as im adding four together im sure they will all blow up??

    The question is can i put an inline diode on the live coming out of each live buzzer wire then connect all four together to the leds to prevent current going to the control box preventing damage again.And what should i do to prevent damage to the leds.Just a point in the right direction is what I need .


    Thankyou again
     
  14. wayneh

    Expert

    Sep 9, 2010
    12,100
    3,034
    A diode on each output would indeed give you an "OR" function. If ANY of the sensors is putting out a signal, the LEDs will respond, but that signal will not zap the other outputs. But don't forget that a diode drops ~0.7v across itself when conducting. So whatever the output was, the new output will be ~0.7v less. That might be fine, but needs to be noted. Also, you might think about what happens when (if?) more than one sensor bank is going off. The flashing could be quite erratic.

    Protecting diodes is all about limiting current - at peak voltage conditions - to ~2/3 of whatever the mfgr says is the max current spec. So if you have a 30mA max LED, running it at ~20mA will help it last forever.
     
  15. plumber1969

    Thread Starter New Member

    May 9, 2011
    16
    0
    Thanks Wayneh

    I understand what you are saying and thankyou.

    With the diode i take it i need to make sure the reverse protection is higher than the maximum output from the other contol boxes

    When the other control box arrive i will link them up and test to see what happens when i set of another bank of sensors, as you say

    With protecting the leds will that be one resistor on the live at the start of the bank of leds .

    Thankyou
     
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