Increase Electric Potential in basic CI

Discussion in 'The Projects Forum' started by Cayo Fontana, Jul 14, 2016.

  1. Cayo Fontana

    Thread Starter New Member

    Jul 14, 2016
    3
    0
    Hi there,

    I'm creating a project that, among other things, consist in two DC Motors (12v) that will rotate in bidirectional orientations (normal and reverse). This CI was done on a breadboard and works fine (see images in annex).

    However this circuit will be controlled by a Raspberry PI (2011.12) (see images in annex). But de output signals by raspberry sends a 2v of electric potential. I need 9v of electric potential minimal.

    How i do that? I read in some blogs that eu can do this using Amplifiers / Mosfets / Transistors.

    In the circuit present with this thread, someone can help me about how i increase the electric potential of 2v (raspoberry signal) to 9v/12v (DC Motor)?

    Thank you!
     
  2. #12

    Expert

    Nov 30, 2010
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    There are several ways to do this.
     
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,539
    1,251
    To reverse DC motors, you probably will need combinations of the Double invert and PI to higher voltage circuits in post #2. These form what is called an H-bridge.

    ak
     
  4. #12

    Expert

    Nov 30, 2010
    16,298
    6,808
    ps, the "PI" label is because these circuits were originally drawn for people using Raspberry Pi controllers.

    Oh, gee...so is this guy.:p
     
  5. Cayo Fontana

    Thread Starter New Member

    Jul 14, 2016
    3
    0
    Hi guys!
    Thank you for your response! Its was extremely useful for me.
    However, i have two questions:
    1) can i use bc547b instead 2n3904?
    2) can you declare all electronics components there are presented in your e-mail (Picture).
    Thank you again!
     
  6. #12

    Expert

    Nov 30, 2010
    16,298
    6,808
    The 547B only goes to 100 ma so I can't say if you can use it unless you tell me how much current you need for the motors.
    I would guess there are many transistors with better gain and higher current ability.
    You ARE going to do the first stage in NPN because 2 volts isn't enough to operate most mosfets.
    You will need diode(s) like the relay drawing to keep the transistors safe from inductive reactance.

    The basic premise for the first resistor is: (Pi voltage -0.6V)/base current = resistance
    where base current is 1/10th of the collector current you need.
    If the Pi can't provide 1/10th of the motor current, you will need at least 2 stages of amplification.

    The base to ground resistor isn't necessary if you're going to stay in low frequency operation.

    The collector resistor might be your motor, or it might be a rather high value resistor just to defeat any leakage current at high temperatures...or it might not be necessary.

    The second stage might not be necessary if your current needs are low enough and the polarity of the signal is correct. But, again, if you need a second stage, the base resistor is supposed to provide 1/10th of the needed collector current.

    Now you have a list of conditions necessary to calculate resistors. Current required, current available from the Pi, voltage from the Pi, speed, temperature, polarity of the drive needed, and how you're going to configure the reversing method.

    I bet you're thinking, "Guess what...coding looks easier than analog design work.":p
     
  7. Cayo Fontana

    Thread Starter New Member

    Jul 14, 2016
    3
    0
    Lol... :D... you're absolutely correct! For me coding is the easy part of this project. Also because i'm programmer (bachelor in computer science in Brazil) and here this graduation emphasizes programming and not eletronics.

    Very thanks for your help and your promptitude. I'm going now buy those items and continue to build this amateur project.

    Thank you again!

    Best regards!
     
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