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Arduino question: unstable signal

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billbyrd1945:
"Peltier? Seriously?"

I realize that no one would think of Peltier as the ideal cooling mechanism. But that's what I happen to have. We bought a wine chiller about five years ago. The two power supplies went belly up. I worked diligently to repair the boards but simply didn't have the knowledge required. So, now I'm replacing the two power supplies with one off-the-shelf unit with enough current to power the two Peltiers (one for the top of the cabin, one for the bottom). I'm sure I've got several hundred hours and some cash invested in repairing it. I knew from the get-go that it wasn't cost feasible. Instead-- I looked at it as a learning experience. But replacing the power supplies was only part of the fix. I had to find someway to marry it to a small break-out board. After failing at that I thought I might have enough Arduino experience to use an Uno to manage the system. I knew I could produce a high and low state to turn on an LED. So why not substitute the LED with Peltiers (going through relays). And shazam! I was actually able to pull it off with the exception of the bouncing back and forth which had the test relay buzzing around on my desk. So, now, I'll Google hysteresis as it applies to writing a proper sketch. If all goes well-- I'll have my wine cooler back, my wife will think I'm a genius, and only you and I will know that Peltiers are the most next-to-nothing cooling devices known to man.  ;D

PS: Volunteers to write the sketch will not be turned away. Top and bottom cabin chill to 60F. A fan for each Peltier comes on after enough heat is produced to warrant cooling them. They stay on for a short while after the Peltier is turned off. Another fan inside the cabin comes on with the Peltier (to draw in cool air). It stays on for a while after the Peltier goes low (to pull in air from the still-cold element).

NivagSwerdna:

--- Quote from: billbyrd1945 on March 18, 2019, 02:32:43 pm ---"Peltier? Seriously?"
I realize that no one would think of Peltier as the ideal cooling mechanism. But that's what I happen to have.
--- End quote ---
IMHO... bin it!

djacobow:

--- Quote from: NivagSwerdna on March 18, 2019, 04:30:10 pm ---
--- Quote from: billbyrd1945 on March 18, 2019, 02:32:43 pm ---"Peltier? Seriously?"
I realize that no one would think of Peltier as the ideal cooling mechanism. But that's what I happen to have.
--- End quote ---
IMHO... bin it!

--- End quote ---

Oh come on now, he's doing it for fun and learning.

There is probably no more project more "Arduino" than your first thermostatically-controlled doohickey.

He's needs to write like 10 lines of code and he's in business.

NivagSwerdna:

--- Quote from: djacobow on March 18, 2019, 04:41:06 pm ---Oh come on now, he's doing it for fun and learning.
--- End quote ---
I know... I feel guilty saying it but Peltier fridges are just ****.  Imagine if he nips out and buys a compressor based cooler... he will be able to cool a nice bottle of wine and then sip contentedly (knowing the performance and operating costs are going to be better) whilst working on a more useful project.
It's a bit like saying, building a solar roadway is a learning experience.  :-DD

... but...

If he insists... considering using an internal ARef (depends on which Arduino is being employed) and then the techniques listed above.  Also consider cooling for the peltier element and having the fan overrun to stop heat from the hot side migrating into the cooler when the element is off - Already mentioned but important.

Mr.B:

--- Quote from: TK on March 18, 2019, 12:56:19 pm ---
--- Quote from: Mr.B on March 18, 2019, 03:30:55 am ---
--- Quote from: billbyrd1945 on March 18, 2019, 03:24:41 am ---Alright then. I won't kick that can down the road. How can I introduce hysteresis into the original circuit? And thank you.

--- End quote ---

You don't introduce it to the circuit as such.
You introduce it to the code.
See the code @djacobow posted above.

--- End quote ---
You can introduce hysteresis control in your circuit or code, depending on your background knowledge (Hardware vs Software person)

--- End quote ---

Yes, you are correct.
However, in this specific case I would suggest the OP will find it considerably easier to introduce it in code.

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