Sous Viduino - using it to control a cold bath?

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so_650
 
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Sous Viduino - using it to control a cold bath?

Post by so_650 »

Hi, folks, I am, as you will recognize, a n00b to Arduino. I'm interested in using the SousViduino setup to drive a cooling element (like your bitchin' peltier unit) to control a regulated cold bath, analagous to the SouVide setup. Indeed, I want to pair the regulated cold bath with the regulated hot bath to optimize a thermal grill.

In reading through the sketch, it's not clear to me where (or if) it needs to be different for running a cooling element rather than a heating element. I am likely missing something. Does the autotuning allow it to figure out which direction its output moves the system?

Thanks for your advice!
RB

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Franklin97355
 
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Re: Sous Viduino - using it to control a cold bath?

Post by Franklin97355 »

The sketch will turn the power on if the temperature is lower than the set point so you would need to modify the code to work the other way. Finding the places where the temperature is checked and an action is taken would be a good start.

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adafruit_support_bill
 
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Re: Sous Viduino - using it to control a cold bath?

Post by adafruit_support_bill »

The last parameter in the PID constructor specifies whether the PID should operate in DIRECT or REVERSE mode:
http://playground.arduino.cc/Code/PIDLibraryConstructor

The SousViduino uses DIRECT control. Just change DIRECT to REVERSE in the following line:

Code: Select all

//Specify the links and initial tuning parameters
PID myPID(&Input, &Output, &Setpoint, Kp, Ki, Kd, DIRECT);

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so_650
 
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Re: Sous Viduino - using it to control a cold bath?

Post by so_650 »

Thank you both!

Franklin, I was hoping the sketch would include "remedial thermostat" language, like: "if T(actual) < T(set) then turn the baby on;"
Alas, 'twas not to be found.

support_bill - Many thanks for pointing out that that's in the PID function. I'll give it a try.

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Re: Sous Viduino - using it to control a cold bath?

Post by adafruit_support_bill »

Code: Select all

 "if T(actual) < T(set) then turn the baby on;"
If you will be using a Peltier device for cooling, that would not work well. In fact, you will also want to operate it at a much higher frequency than used in the SousViduino.

Peltier Devices do not respond well to repeated thermal cycling. Efficiency will suffer and the lifetime of the junction will be short. You should use a relatively fast PWM frequency instead of the TPO output.

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