I want to make a circuit with a slow dc motor, a pot to change the speed of the motor.

Discussion in 'General Electronics Chat' started by Aminnich, Aug 6, 2015.

  1. Aminnich

    Thread Starter New Member

    Aug 6, 2015
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    hey guys, I am new to this thread, not necessarily circuits. I have took a clas in high school on this kinda stuff, but I forgot a lot of it. Now I'm starting a model train layout and I want to do something abnormal things to the layout (also saving some money) so here is my problem..... I want to make a circuit with a slow dc motor, a pot to change the speed of the motor, and a switch to change the dorection of the motor. Im using this for the turnouts. I have googled it, but haven't found anything, I don't even know if it can b done. Thanks for any help!!
     
  2. nerdegutta

    Moderator

    Dec 15, 2009
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    Hi.

    I think it can be done with this circuit:
    dc-motor-controller.png
    It is a 555-timer IC that generates the PWM (Pulse Width Modulation) and a switch to change the direction of the DC motor. With the PWM you control the speed of the motor.
     
    #12 likes this.
  3. Aminnich

    Thread Starter New Member

    Aug 6, 2015
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    Ok, Ummm thanks but do I need a circuit board for that? Could I just use small bread boards under my train layout for that? Sorry I'm not knowledgeable with this kinda stuff
     
  4. nerdegutta

    Moderator

    Dec 15, 2009
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    Under the train... Does that mean there is limited space? Strip boards or perf board will be better.
     
  5. Aminnich

    Thread Starter New Member

    Aug 6, 2015
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    Thier is a lot of room but not a lot of height. Ill look into that stuff, could I buy it all at a RadioShack?
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Everything shows is available in through-hole components to be assembled on perf-board.

    R3 (33 Ohm) is too small. It will allow over 300 mA of base current. The BD139 might handle it, but the high base current will decrease the reliability of both the transistor and the 555. Increase to at least 100 ohms and see how things work out.

    ak
     
  7. #12

    Expert

    Nov 30, 2010
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    RS is basically out of business, but if you can find one, all those parts are common enough it is likely RS would have them. There are a lot of transistors which will fit in the BD139 position. Use at least 35 volt rated, 1 amp rated and don't worry about heat. It's a saturated switch. They don't suffer much from overheating. This one will suffer about 0.3 watts. Too much for a TO-92 transistor package, but a TO-220/TO-234 should work nicely.
     
    Last edited: Aug 6, 2015
  8. Aminnich

    Thread Starter New Member

    Aug 6, 2015
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    Im not sure what I want to do, I have a bunch of ideas I want to try, but im going to eventually probably going to need some kind of circuit. As for RadioShack, I have a 1 close to my house yet, not much in stock, but he can order stuff for me. Like I said before, I don't know much about this kind of stuff
     
  9. #12

    Expert

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    There are several on-line vendors to mail parts to you, if all else fails. The decision point is about price of shipping vs high prices in a RS store.

    mouser, jameco, digikey, to name a few.
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    ....Or $5.00 on ebay 291341338166 just need the reversing relay.
    Max.
     
  11. Aminnich

    Thread Starter New Member

    Aug 6, 2015
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    What would a reverse relay do???
     
  12. #12

    Expert

    Nov 30, 2010
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    Reverse the motor. Shown as S1 DPDT in post #2.
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    OP: Which incidentally should be done with the motor rpm at zero.
    Max.
     
  14. Aminnich

    Thread Starter New Member

    Aug 6, 2015
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    So the direction of the motor would switch when the potentiometer went to zero automatically??? That sounds good
     
  15. #12

    Expert

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    No, the direction of the motor reverses when you energize the relay coil or de-energize the relay coil.
    There is no connection from any potentiometer to the relay coil. In fact, I don't see any relay coil in the schematic. That will be another circuit which you have to add. It will probably be a SPST switch labeled, "forward" and, "reverse".
     
  16. MaxHeadRoom

    Expert

    Jul 18, 2013
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    For Relay, Read DPDT switch.
    Relay optional.
    Max.
     
  17. Aminnich

    Thread Starter New Member

    Aug 6, 2015
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    At this point, I want it as simple as possible. If the reverse relay can get rid of some things great.
     
  18. Aminnich

    Thread Starter New Member

    Aug 6, 2015
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    Also im goig to want to add LEDs to the circuit for the control panel, telling me which way the switch is facing for the track turnout... But that isn't as important
     
  19. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If you opt for the ebay route, you will need the DPDT S1 in post #2 for reversal.
    Simpler than a relay.
    Max.
     
  20. Aminnich

    Thread Starter New Member

    Aug 6, 2015
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    Ok sorry, Im confused, R u still using the first diagram???
     
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