I'm beginning my trek into the Arduino world with a temp control project for my finances pet Tarantula.
The tarantula lives in a 0.0216 m^3 tank. Optimal conditions suggest a temperature of around 25 degrees Celsius. I haven't figured out the hardware for the thermometer yet. I want to focus on the control scheme then look into what kind of circuit hardware I'll need. I don't want much more than a +/- 3 degree temp fluctuation over a given 5 minute period. I'm looking at the PID controller because I know that overshoot, rise time and settling time are things that I need to consider when attempting to keep the arachnid at a comfortable living temp. Can I get some suggestions and/or help in approaching this project from a controls and hardware stand point. Thanks for any assistance.
The longer latency you allow in making temperature adjustments, the more uncertainty you get in the control scheme. So for openers, if there is no disadvantage to quickly detecting and adjusting temperature, that is what I would do. Experiment will be necessary to determine how long to activate the heater, because if you wait until your temp sensor reaches the desired temperature, you'll probably overshoot.
Also, take a look at thermistors to measure temperature. I have one controlling aquarium temperature. Comparing it to a high-quality lab thermometer, it appears to be always within 0.5 deg. F of the lab thermometer. They cost next to nothing, and are too simple to fail.
heat is based on power.
controls are based on power.
in order to change from 0 deg c to 25 c in 30 seconds, you need a lot of power
to move from 24 c o 25 c in 3 minutes, not so much power.
if you need a lot of power, get a high power SSR, might even be a good choice for a little power.
I would offer that you can buy a heating pad from a store, glue it to the bottom of the tank and then put your thermometer inside somewhere. then control that bad.
You want to look at PID control, there is this library / links in the Arduino Playground using the common encapsuled ds18b20 sensor, though no reason the code could not be changed for a ntc sensor.
The code does work, have used it myself.