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Flasher circuit negative switching

Discussion in 'General Electronics Discussion' started by dangrsdave, Jul 3, 2012.

  1. dangrsdave

    dangrsdave

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    Jul 3, 2012
    I have an 05 Saturn Ion that has a malfunctioning body control module. The circuitry to flash the front signal lights has been damaged (common problem). I could replace the body control module however it is very expensive (upwards of $600) and also requires reprogramming by a GM dealer (additional expense). I am trying to come up with a low cost work around with some simple circuitry to bypass the BCM. My problem is however, this vehicle uses switching from a single wire connected to three switches with three different resistance(s) to ground. I have a basic understanding of electronics and got as far as I could but I am having difficulty working out how to get the switches to turn on the relays. Anyone have knowledge of transistor or IC circuitry that can complete this schematic?

    [​IMG]
     
  2. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Welcome to the forum.

    I have a few questions.... Where did you get the schematic? Are the transistors shown accessible? If they are, do you know if they're good?

    .
     
  3. dangrsdave

    dangrsdave

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    Jul 3, 2012
    I drew this schematic. This is not the BCM. I found the flasher circuit and the regulator circuit and incorporated them into the schematic. I drew the relays and started to figure out how to connect them to some transistors but this needs to be worked out. The switches on the top right are in the steering column and cannot be altered.
     
  4. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    The ADC input of an inexpensive microcontroller (uC) will handle this and its outputs can drive those transistors. With a uC you won't need the flasher circuit either.
     
  5. dangrsdave

    dangrsdave

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    Jul 3, 2012
    That's a little beyond my knowledge. Can you show me how to make that work?
     
  6. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
  7. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Are you sure of the Values of R5, R6? They seem excessively low, like they have a misplaced decimal point.
     
  8. dangrsdave

    dangrsdave

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    Jul 3, 2012
    Yes, R5 and R6 where measured resistance. I will double check the scale. Also FYI... Sw1 can be closed simultaneously with Sw2 or Sw3.
    However Sw2 cannot be closed when Sw3 is closed and visa versa.
     
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    How are you measuring this? These measurements should be made with all switches opened and the common input wire disconnected.
     
  10. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Oops! Since you probably can't access these resistors you should measure from ground to the common input wire, while closing each switch. Take the measurement and open the switch before closing the next one and taking your next measurement. The common input wire still needs to be disconnected from anything else.
     
    Last edited: Jul 4, 2012
  11. dangrsdave

    dangrsdave

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    Jul 3, 2012
    Actually did (do) have access to the resistors but yes measured open (disconnected from any ground source or input source)
     
  12. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    So, you're saying that those values are correct? EEK! :eek:
     
  13. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    You seem to have disappeared while I've been waiting for definitive answer to the values of those resistors. Those resistors are used in conjunction with an ADC input on your control unit but I don't see how the circuit could function with values like that, Attached is a circuit intended to replace your current one while utilizing the steering column resistors but not with the values you measured. They make no sense at all.

    Please note that this is a rough draft. An Automobile's environment is harsh, so additional filtering and spike protection will be in order. I used four relays because you did but two DPST relays will do the job. Two SPST relays will suffice too but a DPST will split the current load between the two contacts.
     

    Attached Files:

    Last edited: Jul 11, 2012
  14. dangrsdave

    dangrsdave

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    Jul 3, 2012
    I've been extremely busy and haven't had a chance to pull the switch off again. Your circuit looks promising. I could possibly change the resistors. What values would work?
     
  15. dangrsdave

    dangrsdave

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    Jul 3, 2012
    Well this is embarrassing but I have the resistance values wrong for r5 and r6. I had my meter set on diode. Anyway the correct values are R5 = 0.990K, R6 = 3.570k ohms respectively.
     
  16. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    I modified the attachment in that post, so take a look. Normally I'd use much higher values but since this is a noisy automobile environment I lowered them. You may find that they have to be scaled by 10:1. For certain, this circuit needs to be completely prototyped external of the auto using a mock turn signal & emergency switch.

    Here's an updated schematic with some changes and quite a bit of noise prevention added. Any experienced members who have dealt with the nasty auto environment are invited to add comments. I would also appreciate any input as to how and why dangrsdave's resistors would or could be as low as he measured them.

    EDIT: The resistor values question has been answered by dangrsdave in a subsequent post. This schematic has been updated to reflect the existing resistors.
     

    Attached Files:

    Last edited: Jul 11, 2012
  17. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Ah, you found a short circuit between the ears! :p:D

    I'll update the schematic to reflect the existing resistors.
     
  18. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    I've modified the last schematic to reflect your existing turn sig resistors.
     
  19. dangrsdave

    dangrsdave

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    Jul 3, 2012
    Wow CDRIVE, your circuit looks promising. What do you estimate the rough cost of the components and where is a good source? I will definately test it well before I call it done.
     
  20. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Not including the relays and a PC board, there's less than $12.00 worth of components. Where to purchase them depends upon where you live. Keep in mind that U1 is a Microcontroller, which must be programmed.
     
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