Author Topic: PID question  (Read 1035 times)

Offline Stevie

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PID question
« on: November 13, 2014, 03:08:04 AM »
While I'd love to build up a brewpi, I don't want to spend $200-ish on temp control. My question is simple. Do PID controllers with built in relays exist, or do I need to add solid state relays? Just looking to keep it simple and less than $60.

S. cerevisiae

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Re: PID question
« Reply #1 on: November 13, 2014, 07:50:09 PM »
What are you attempting to accomplish?

Offline Stevie

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Re: PID question
« Reply #2 on: November 13, 2014, 07:54:06 PM »
Control heat and cooling in my freezer. While I like the stc-1000, I get a lot of over cooling and would rather not. My other thought was to build a dual stc, one for hot and one for cold so the trigger points could be independent.

S. cerevisiae

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Re: PID question
« Reply #3 on: November 13, 2014, 08:03:43 PM »
Embedded control with something like a BrewPI is more expensive to start off, but it's more flexible in the long run.  I have started a thread to see if there is any interest in learning about how embedded systems work.
« Last Edit: November 13, 2014, 08:56:52 PM by S. cerevisiae »

Offline Stevie

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Re: PID question
« Reply #4 on: November 13, 2014, 08:17:40 PM »
Embedded control with something like a BrewPI is more expensive to start off, but its more flexible in the long run.  I have started a thread to see if there is any interest in learning about how embedded systems work.
Yeah, I really want a BrewPi, but it is a large investment and the bells and whistles are not necessary, but very cool. I might ride out the STC for a bit longer and go BrewPi. Maybe wait for the next shield revision.

Offline niels

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Re: PID question
« Reply #5 on: November 13, 2014, 09:04:21 PM »
The Model T of Brewbit is also a very compelling alternative. It's a nice all-in-one setup instead of the BrewPi with all the wires and modules.

I have a BrewPi, but I'm anxious to upgrade to a Model T.

- Niels

Offline Stevie

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Re: PID question
« Reply #6 on: November 13, 2014, 09:23:43 PM »
The Model T of Brewbit is also a very compelling alternative. It's a nice all-in-one setup instead of the BrewPi with all the wires and modules.

I have a BrewPi, but I'm anxious to upgrade to a Model T.

- Niels
Would be nice to have something that works out of the box. I'll need to dig up some reviews.

S. cerevisiae

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Re: PID question
« Reply #7 on: November 13, 2014, 09:34:59 PM »
In reality, the Arduino just adds unnecessary complexity to the design.  The control system could have been implemented using only the Raspberry PI because the BrewPI only uses digital I/O.  My guess is that the project started out as an Arduino project with the Raspberry PI being grafted on at a latter date. 


With that said, I laud the effort that the designer put into bringing this product to the market.  There's a lot that goes into bringing a product to market that's above and beyond the basic software and hardware engineering work. For example, the case in which the unit resides did not design itself, and the documentation and website did not magically appear out of thin air.


Offline Stevie

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Re: PID question
« Reply #8 on: November 13, 2014, 10:03:05 PM »
In reality, the Arduino just adds unnecessary complexity to the design.  The control system could have been implemented using only the Raspberry PI because the BrewPI only uses digital I/O.  My guess is that the project started out as an Arduino project with the Raspberry PI being grafted on at a latter date. 


He discusses this on his blog. Can't remember the full explanation, but it was something like the pi was not stable and reliable enough to do it on it's own. In this setup the pi sends the commands to the arduino, and as long as there is power, the arduino will run it. If the pi fails, the ardunio will continue to run its last set of commands. The pi then acts as a webserver for the interface.

S. cerevisiae

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Re: PID question
« Reply #9 on: November 14, 2014, 01:29:24 AM »
I would like to know the full details.  Neither system is hardened for fail-safe operation. The Arduino is just as likely to fail as the Raspberry PI.   

Offline Stevie

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PID question
« Reply #10 on: November 14, 2014, 01:45:26 AM »
Check out his site and forums. He is very active.

Offline Stevie

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Re: PID question
« Reply #11 on: November 16, 2014, 05:56:42 AM »
Seems Elco is looking into switching from arduino to a spark based platform. I knew they maxed out the onboard memory of the arduino, but it also sounds like he will be able to develop these cheaper. Bonus is the spark has embedded wifi allowing for it to communicate with the pi wirelessly.

https://community.spark.io/t/looking-for-feedback-on-brewing-shield-with-touchscreen/7203

S. cerevisiae

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Re: PID question
« Reply #12 on: November 18, 2014, 09:03:55 PM »
I do not agree with his assertion that the Pi can crash whereas the Arduino is fail-safe.   All microprocessors and microcontrollers can crash.  That's why fail-safe systems have built-in redundancy.

Offline Stevie

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Re: PID question
« Reply #13 on: November 18, 2014, 09:42:08 PM »
I do not agree with his assertion that the Pi can crash whereas the Arduino is fail-safe.   All microprocessors and microcontrollers can crash.  That's why fail-safe systems have built-in redundancy.


Sure, nothing is fail safe. I think he means that the ardunio is more reliable as it cannot have an OS crash like a pi which is a full on computer. I'm sure plenty of bad could happen.