how to control a DC motor

Discussion in 'The Projects Forum' started by bigabeast96, Feb 12, 2015.

  1. bigabeast96

    Thread Starter New Member

    Feb 12, 2015
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    hello im new to this forum and need some help i have a pic circuit connected to a relay which has a DC motor which i need to control using temperature, does anyone have any tips on how to do this? Thanks upload_2015-2-12_21-10-0.png
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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  3. bigabeast96

    Thread Starter New Member

    Feb 12, 2015
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    thanks for the reply max but i should of specified it was more the speed of the motor i was looking to control rather that the revering it
    Alan
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Your drawing shows a basic On/Off method?
    What is the source and nature of the control signal?
    Max.
     
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Could use a thermister, neg temp coef., fixed resistor & voltage controlled PWM like this:
    Sgt W PWM 00000.png ; resistor is top of pot, TCR bottom of pot. There are other forms in Bill's Blog?
     
  6. bigabeast96

    Thread Starter New Member

    Feb 12, 2015
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    I have a thermistor connected to a pic chip which is programmed to turn the relay on when the thermistor reaches 20°C. I tried connecting another themistor in the relay, in a potential divider set up but still doesn't seem to work . upload_2015-2-12_21-43-27.png
     
  7. Dodgydave

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    Jun 22, 2012
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  8. Reloadron

    Active Member

    Jan 15, 2015
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    This sounds like you want to control a motor speed based on temperature, for example as temperature increases motor speed increases. Something like fan speed control based on temperature rise? Would that be where you are going with this? Should that be the case and you want micro controller control run an analog voltage from your thermistor or temperature sensor and have the uC output a PWM to the motor based on temperature.
    You really need to better explain what you are trying to do.

    Ron
     
  9. Dodgydave

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    Jun 22, 2012
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  10. bigabeast96

    Thread Starter New Member

    Feb 12, 2015
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    Thanks everyone who replied i used the link to the simple PWM circuit based on the 555 timer and connected the output pin on my microcontroller to pin 4 (reset pin) on my 555 and now the themistor connected to the microcontroller acts as a threshold temperature and the second thermistor controls the frequency of the 555. Im not really great at explaining things but i hope you understand thanks again for helping

    upload_2015-2-13_22-6-51.png
     
  11. Reloadron

    Active Member

    Jan 15, 2015
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    Here is what I don't understand. It looks like (your drawing is very small and hard to read) you have the thermistor and resistor forming a voltage divider whose Vout will change with temperature, but it looks like that analog voltage is going to a digital input to your micro controller. This does not seem like you will have a reliable threshold. What micro controller are you using? The 555 RST is tied to a Q output? I don't understand that? Finally the 555 Out is driving a NPN transistor used as a switch for the fan. Wouldn't this be better if the fan was in the transistor collector rather than emitter? Finally you may want to place a 0.1uF cap across the motor terminals and a snubber diode.

    Finally depending on the micro controller why not run the thermistor signal into an analog input and let the micro controller drive the fan through a transistor?

    Ron
     
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