Can A Phototransistor Be Intergrated?

Discussion in 'The Projects Forum' started by JDR04, Apr 4, 2012.

  1. JDR04

    Thread Starter Active Member

    May 5, 2011
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    Please see the attached circuit.

    I'm thinking of building this circuit but would like to know if the following modifications can be done;

    1. How would I go about running the circuit off a 9V battery instead of 5V?

    2.Is it possible to INTERGRATE A phototransistor into the circuit? Then have a switch that will give the option of sound detection or light detection. How can this be done?

    3.Is the 5V in this circuit connected to R4 or is it perhaps just a bad copy of the drawing? Would it make sense to do this in other words?

    Thanks for you help and your time - JDR04
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    Your circuit uses a 3-wire electret mic which is rare. Most electret mics have only 2 wires (signal and ground) and require a resistor to power them.

    Your circuit uses a lousy old 741 opamp that is 44 or 45 years old. It was designed to work only with a 30V supply. Many do not work with a 10V supply. It is too noisy for audio (hiss) and its bandwidth goes to only 9kHz.

    Your opamp is inverting with a very low input resistance that loads down the mic. It should be non-inverting with a high input resistance.

    Your transistor has no base bias voltage so it will not work. It also has no emitter resistor to stabilize the bias.
    Of course +5V is connected to R4. Without it then the transistor will do nothing, but since its bias is wrong anyway then it does nothing anyway.

    You must learn something about phototransistor circuits if you want to use one.
     
  3. CDRIVE

    Senior Member

    Jul 1, 2008
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    Yes, R4 is connected to +5V. What are you trying to build?

    Edit: I see AG has preempted my post. You're in good hands and I'm spread too thin anyway.
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    We need to have a separate forum for nOObs who are taught NOTHING by their school teachers. Then they can learn the basics there.
    You know, one plus one= threeee!:rolleyes:
    Oh, maybe the teachers must learn basic arithmatic first.
     
  5. CDRIVE

    Senior Member

    Jul 1, 2008
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    JDR04, don't let AG's bark deter you. In between all that barking he'll give you solid information, more barking, schematics and more good info, perhaps a yipe or two and more good stuff. :rolleyes: Endeavor to persevere. ;)
     
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  6. JDR04

    Thread Starter Active Member

    May 5, 2011
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    Hello Audioguru, thanks for the information which was constructive.

    Yes I am a n00bie as you put it and am doing my best to learn. Going back to school would be out for me as I am 54 now.Besides the school I did go to did'nt have electronics as a subject but the teachers were brilliant.

    It was only when I emigrated to Scotland did I get the opportunity to delve into electronics as a hobby. I find it fantastic although its late in life.

    Your constructive information was good for me and I appreciate it enormously but the rest of your rant I dont think encourages many people and certainly does not do a lot for this wonderful forum.

    Thanks for your time anyway - JDR04 (n00bie & proud of it)
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    My rant was about the school systems in certain countries today.
    Electronics is taught by gym teachers who know nothing about electronics.
    Some teachers can barely speak the language of the students.
     
  8. Adjuster

    Well-Known Member

    Dec 26, 2010
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    What Audioguru said may be blunt, but until you have enough knowledge to be aware of the flaws in a circuit like this fairly easily, it may be better for you to try to get hold of more reliable sources for circuits to build, perhaps from kits.

    There is an awful lot of stuff around on the Internet especially which is very old and may have been copied many times with mistakes creeping in, or may simply never have been any good in the first place. Some of them may have originated from real noobs who know less about the subject than you do, so beware!
     
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  9. Audioguru

    New Member

    Dec 20, 2007
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    Many times a circuit shown to blink an LED with a music source from an Instructables was posted here. It is absolute garbage because it destroys the signal source amplifier, destroys the transistor and destroys the LED because it was designed and posted by a 10 years old kid who knows NOTHING about electronics.
    There are millions of circuits on the internet that DOO NOT WORK!
     
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  10. DickCappels

    Moderator

    Aug 21, 2008
    2,647
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    You can use 1/2 LM358 -easy to get and they run down to about 3 volts. Sure, the audio quality will be very poor compared to most modern op-amps, but you will get to see your circuit work.

    The NPN transistor amplifier needs some sort of bias. I suggest biasing the base at 1 volt with a voltage divide such as you have on the input to the opamp, then putting a 100 ohm resistor in series with the emitter (off the top of my head for starters). You might do well to just eliminate the resistor stage if you are going to drive a light load.

    Let us know how it comes along!
     
  11. JDR04

    Thread Starter Active Member

    May 5, 2011
    339
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    I've taken your guys advice and have abandoned the idea of that circuit. I'm still pleased in a way I found it because the information given by guys like yourselves (and my good friend Audioguru) certainly has helped me learn something.I suppose it's all a process which requires patience.

    I've found another circuit (I can hear Audioguru sigh from this side of the pond) and am going to have a bash at it. Basically I'm attempting to activate a camera via a sound detecter circuit. Any suggestions will be appreciated.

    Anyway, thanks for everything guys and no doubt I'll be asking more silly questions. - JDR04
     
  12. chrisw1990

    Active Member

    Oct 22, 2011
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    woah wait.. its three? *checks calculator* wait a minutee... ¬¬ ha i remember my electronics classes.. shocker
     
  13. Audioguru

    New Member

    Dec 20, 2007
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    Calculators were not invented yet when I went to school. I got my first calculator when I finished high school.
     
  14. chrisw1990

    Active Member

    Oct 22, 2011
    543
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    i am ashamed to say, everytime i have an exam, i forget mine.. and have to buy a new one.. i have too many now it is ridiculous lol
     
  15. CDRIVE

    Senior Member

    Jul 1, 2008
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    Ah, we have outcome based education now... Whatever that means? Anyway, we can't tell a student that 1+1=2 when he or she thinks it's 3. That would be judgmental and make the student feel bad. :rolleyes:
     
  16. CDRIVE

    Senior Member

    Jul 1, 2008
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    I miss my pocket protector and slide rule. It's was the late 70's when I bought my first calculator. The super HP25 with RPN. Still have it, though it's an energy hog. ;)
     
  17. Audioguru

    New Member

    Dec 20, 2007
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    I still have my slide-rule somewhere. My daughter showed it at school and the kids laughed at it.
     
  18. CDRIVE

    Senior Member

    Jul 1, 2008
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    That's got to be a typo. You did mean Granddaughter, didn't you? :D
     
  19. Audioguru

    New Member

    Dec 20, 2007
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    My daughter is 32. She showed my slide-rule at school about 18 years ago.
     
  20. CDRIVE

    Senior Member

    Jul 1, 2008
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    Ah, now that adds up correctly. :D
     
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