Electronic Issues

Discussion in 'The Projects Forum' started by savingaurora, Jan 11, 2010.

  1. savingaurora

    Thread Starter New Member

    Jan 11, 2010
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    I'm currently building a circuit and writing a program in PicBasic for a baseball machine. I built one board that is working perfect but every attempt I've made to remake that board has ended up in headaches and trouble. I've been searching this forum for answer and found great results but nothing that pertained to my situation.

    This is my circuit:
    [​IMG]

    The only difference between the original board I made that is 100% working and the ones I'm having trouble with would be the transistors that i'm using. The original transistors I used were the 2n2222 NPN trans. The newer boards I'm using the 2n3904 and the 2n4401 but from what I've read online it seems that I can just replace with those transistors without any issue.

    I've noticed that when I test the board I can get the automation to do right.
    (It cycles and feeds Q2 and Q3 5v in the sequence I need them to) As soon as I feed Q1 with 5volts from my PIC the entire board stops working. I'm assuming this is a transistor issue or an issue with biasing but have yet to find the exact problem..

    I'd appreciate the help and if you have any questions because I'm sure my explanation is pretty confusing. Feel free to ask

    thanks in advance

    EDIT: Also some issues I'm having that I forgot to describe is when the transistor switches sometimes it hold 5V on the base of the transistor. I've also had one board where one of the pins on the PIC was showing 10-12 volts (note that this is a pin that is connected to one of the transistors).This happens regardless if I have the microchip in the socket or not. So I know it isn't an issue with my programming or the chip itself
     
    Last edited: Jan 11, 2010
  2. SgtWookie

    Expert

    Jul 17, 2007
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    What are the transistors switching? 2N2222's are rated for Ic=800mA, 2N3904's; 200mA, 2N4401's; 600mA.

    If it's relays or solenoids (basically, inductive loads), you need to have protection diodes on all of them, like on Q3.

    It sounds like your transistors got blown, and are shorted from the collector to base.

    Consider using more capable transistors, or perhaps Darlingtons.

    You could replace the discrete transistors with a single ULN2066B quad Darlington array:
    http://ca.mouser.com/ProductDetail/...=sGAEpiMZZMutXGli8Ay4kAHmCxIxFTXSEZuhf4fL/N0=
    http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=497-6788-5-ND
    Datasheet: http://www.st.com/stonline/products/literature/ds/1534/uln2066b.pdf
    The base resistor and protection diodes are built in; and they can sink up to 1.5A.
     
    Last edited: Jan 12, 2010
  3. savingaurora

    Thread Starter New Member

    Jan 11, 2010
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    this actually sounds like a great idea and I'll probably order a couple today and see how it all works out. I figured I was blowing the transistors but I couldn't find the right information anyways. Thank you so much wookie. I'll try this out probably tomorrow.

    Thanks again

    EDIT: Also I forgot to mention this but the transistors are switching a piezo speaker(Q2) and 2 different air Valves on (Q1 and Q3). Note that Q1 isn't being used so it isn't set up with a protection diode just yet. The Connection that R7 is connected to is just setup as an interrupt switch. The connection that R6 is connected to has a photocell in that connection to get readings of the lighting (setup with a laser diode as a light switch.)
     
    Last edited: Jan 12, 2010
  4. savingaurora

    Thread Starter New Member

    Jan 11, 2010
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    I ran to a local electronic store and picked up 3 ECG2086 (is suppose to be a cross reference to the ULN2066B.) I also ordered a couple of the ULN's from Digikey.
    Fingers crossed... but I hope my wiring isn't :D
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    LOL!

    OK, keep in mind that you want to connect pins 1 and 8 to your +12v supply. That will protect the outputs of the Darlingtons.

    Pins 4, 5, 12, and 13 all get connected to ground.
     
    Last edited: Jan 13, 2010
  6. savingaurora

    Thread Starter New Member

    Jan 11, 2010
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    I hate to seem like a non-happy prick I only have 1 tiny question. When looking up the datasheet you linked to (and all the datasheets it was cross-referenced with), it's showing the pinouts of the ULN2066B as.

    Label | Pins
    -------------------
    C | 2, 7, 9, 16
    B | 3, 6, 11, 14
    K | 1, 8
    GND | 4, 5, 12, 13
    -------------------

    so for the protection diodes to work wouldn't it be pins 1 & 8 not 1 & 9?
    I don't mean to get online and question your advice...as I see you do help a lot of people on this forum. I'm just making sure i don't have anything mixed up.

    sorry for all these questions.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    You are correct!
    I was looking at a datasheet for the 2064, 2066, 2068, 2070, 2074, and 2076 - and happened to look at the diagram for a 2068/2070 instead of a 2064/2066.

    That's what happens when too many projects are on the fire at once. I'm glad you caught my mistake before things got toasty...
     
  8. savingaurora

    Thread Starter New Member

    Jan 11, 2010
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    SgtWookie you are a GOD. I hooked up the ECG2086 chip today. Worked like a charm. Thanks so much for your help and I hope to learn my **** and help contribute on this forum later on.

    Thanks for everything
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    I am not a diety! Sometimes I feel like a false prophet. :rolleyes: ;) But frankly, I did not realize that particular series has different pinouts; as to why they are different, I have no clue.

    I'm glad your results were successful :)
     
  10. savingaurora

    Thread Starter New Member

    Jan 11, 2010
    8
    0
    sgtwookie i wanted to show you my most recent revision... thanks for all your help and hope this makes it seem worth it, helping so many people i mean

    http://trexcastille.com/mashburn/bbmachine.3gp

    -drake

    *edit* the only difference from the original circuit is an added relay to save the ULN2066B from blowing because that solenoid drawing 2.16 amps. The switch also has been replaced with a laser diode and photocell... a light switch (the red light in the collar)
     
    Last edited: Mar 5, 2010
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