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(PIR) Motion senser controlling CPU fan speed with trinket?

Discussion in 'General Electronics Discussion' started by Dragonspainter, Dec 28, 2016.

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  1. Dragonspainter

    Dragonspainter

    1
    0
    Dec 27, 2016
    Me and my brother are working on a project together and I was hoping for some advice. While I am familiar with some electronic babble, my experience is pretty much exclusively with LEDS... To say I am out of my comfort zone is a light way of putting it lol
    But we are doing this project to learn, and learn I shall!


    Basically the project is some fans partially controlled with a PIR(motion senser). The fans are always on at the "low" speed, but when the motion senser detects movement the fans turn on high for a amount of time before turning back to low afterwards. Rinse and repeat.

    The motion senser I was planning on using was https://www.adafruit.com/products/189
    It runs on 5V-12V power, Digital signal output is 3.3V high/low.

    The fans are these https://www.amazon.com/F12-PWM-PST-...&qid=1481148700&sr=8-1&keywords=arctic+5+pack
    Voltage: 0.25A / +12V
    They can be daisy chained together and are PWM controlled if need be. I plan on running 2 fans with this project. These fans can run on as low as 5 volts (I double checked)

    For the microcontroler I was planning on using the ADAfruit trinket https://www.adafruit.com/product/1500 (the 5V one)

    As for the power supply we where planning on using a 12V adapter we had laying around.


    My current plan is to have the fans power connected to the USB + Output pin and having them run on a base voltage of 5 volts at 500mA (the low speed). the PIR power will connect to the trinket power regulator output pin which supply 5 volts at 150mA. Ground wires go to ground pin. the PIR digital output would connect to the fans so when its triggered it will supply the fans a extra 3 volts of power(the higher speed). I can adjust the timer using the potentiometer that comes on the PIR senser all the way up so it lasts about 4 minutes when triggered. The trinkets power will be supplied by the 12 volt wall adapter.

    My main problem is will this even work? Will connecting the 3 volt PIR digital output to the wire that's already supplying the base voltage of 5 volts actually increase it to 8 volts? Will it cause some-sort of feedback and burn out the trinket? In my mind I don't see any issues but I simply don't know enough on the subject to know what I don't know!

    My second problem is; Do I even need the trinket? The original plan my brother and I came up with was to control the speed of the fans using PWM and a bit of code to control the timing, but that was before I found out the PIR had a potentiometer. At this point it seems like I am using the trinket as a voltage regulator, not a micro-controller. Should I find a voltage regulator instead? What would you suggest?

    My third problem is the fans low speed would be 5 volts and their high is only 8 volts. Not much of a improvement. I'm thinking about upping that to 12 volts via a step-up booster. But do they even make step up boosters that go from 3 volts to 7 volts? I know these particular fans work at 5 volts, so that's not an issue.

    Lastly; Is there a better way to do this?

    Thank you in advance for reading my woes, and any advice you have is appreciated.
     
  2. Rayregula

    Rayregula

    84
    18
    Dec 20, 2016
    You can't add 3V to 5V it will stay at 5V. The higher voltage cancels out the lower one. Boosting it would work just boost it above 5V lets say 10V the 10 volts will stop the 5 volts from flowing giving your fan 10V just make sure to add a diode to keep your high speed voltage from entering your power source. There is actually quite a bit of difference between running a fan at 5v vs 8V. You could go to 12V if you would like but it can get a bit loud.
     
  3. Rayregula

    Rayregula

    84
    18
    Dec 20, 2016
    Or you could use a 5V relay. I can get mine to click over at 3.0V-3.1V at 40ma
     
    Last edited: Dec 29, 2016
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