[Noisebridge-discuss] can you write a PID loop for humidistat in Arduino

[Gopiballava Flaherty]

How accurately do you think you need the humidity control to be?

PID loops are usually used when you need really accurate control of something complex, such as making a motor spin at a particular velocity even when the load on it is changing. 

For a simple binary system like this I think that turning on the humidifier when the humidity is low would be enough. It should have some combination of hysteresis and rate limiting. 

IE: it should wait a few minutes after turning the humidifier on before turning it off even if the sensor says it's time. And vice versa. So that you don't have it going on and off a couple times a second. Hysteresis would be a separate level for turning on or off. 

Eg: if humidity drops to 70%, turn on humidifier. But don't turn it off till humidity reaches 75%. This also helps keep the system from cycling the humidifier quickly. 

Thanks,

gopi at iPhone


On Oct 26, 2011, at 2:12, Jake <jake at spaz.org> wrote:

> Hello mushroom fans (not the spinning kind)
> 
> I have stepped up to make this arduino-based humidity controller for the 
> noisebridge mushroom project.  I have hooked up the SHT15 humidity (and 
> temperature) sensor to the arduino, and i'm getting readings of 
> temperature and humidity.
> 
> I will now attach a relay to the arduino, and make it so that it can 
> control the relay from a pin.  That relay will be wired to an AC socket so 
> that the humidifier above the mushroom closet can be activated by the 
> arduino.
> 
> The goal is to maintain the specified humidity inside the mushroom closet. 
> When it gets too low, the humidifier turns on.
> 
> I understand we need a PID loop, which stands for Period Interval Delta or 
> something like that.  Basically a software loop which reads the humidity 
> and decides when to turn the relay on and off to achieve a smooth 
> humidity-regulating action.
> 
> Here is an arduino PID library discussion (it's already written)
> http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1226431507
> 
> and here's the arduino sketch which reads the humidity/temperature sensor 
> (and just displays it out the serial port)
> http://wiring.org.co/learning/basics/humiditytemperaturesht15.html
> 
> if you are a good programmer and would like to help the mushroom 
> cultivation happening at noisebridge (and elsewhere) please write to me 
> indicating your interest in doing the software for this project.
> 
> thanks!
> -jake
> _______________________________________________
> Noisebridge-discuss mailing list
> Noisebridge-discuss at lists.noisebridge.net
> https://www.noisebridge.net/mailman/listinfo/noisebridge-discuss