[time-nuts] temperature sensor
albertson.chris at gmail.com
Mon Jul 21 12:48:38 EDT 2014
I tried the
On Mon, Jul 21, 2014 at 7:02 AM, Attila Kinali <attila at kinali.ch> wrote:
> How about doing it the old analog way? Feed the output of the
> PID controller to comparator together with a sawtooth signal.
> That will give you a quite nice 0-100% PWM control.
> I'm quite sure a similar solution is possible with a NE555 as well.
I tried an analog controller first. It is very hard to implement a tunable
PID controller that does PWM without using a bazillion chips. My second
controller worked much better and a I wrote, uses only a single 8-pin DIP
chip. The AVR uP has more analog inputs and outputs then you need and
costs about $1.25
As for the fan startup. What you do is test it and store the minimum fan
voltage in a constant and use that as the zero point. So the "P" part of
the PID sets the fan voltage to the temperature error times a constant plus
the zero point.
A better solution is to use a tachometer fan. Then the controller does not
set the fan voltage but sets the fan speed. there are still extra pins on
the controller and this is one upgrade and the other upgrade is to measure
absent air temperature But the simple controller does well enough.
I don't see any reason at all to build a PWM controller with a comparator.
Multiple sets of that hardware is built into every uP and they cost nearly
nothing and come in a single 8 pin DIP.
> Of course, you would need to adjust the PID controller parameters
> to accomodate for the new element in the control loop.
> Attila Kinali
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