Proportional fan control. I suck at math!

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  1. - 2nd January 2010, 15:00 #1
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    polymer52
    polymer52 is offline Junior Member
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    Default Proportional fan control. I suck at math!

    I have a solar collector controller and I need to build a proportional fan controller for it and I need some help with the math. I need it to be proportional from 90 to 120 deg F and off below 90 deg.
    I'm using an LM34 temp sensor that outputs 10mv/degree F and I want to use a PIC with a hardware pwm to drive a DC fan. I haven't chosen the pic yet.
    Below 90deg F I need a 0% duty cycle (off), at 90deg F (.900 volts at the pic) a 50% duty cycle and at 120deg F and above (1.20 volts at the pic) I need 100% duty cycle..
    I know you guys are geniuses so I'm hoping someone can come up with a formula for this.
    Thanks.
    Last edited by polymer52; - 2nd January 2010 at 15:04.
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