Wine Cellar Controls: Simple analog control for Temperature and Humidity

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lukezautke 19 years ago

While not the most electronically-inclined individual, I am a computer scientist--but have little grasp on the hardware (especially analog) side of these things. I have the need to construct a control mechanism for my wine cellar. Here are my specs:

I need two "threshold sensors," one for temperature (which will be a thermostat) and one for humidity (is there such thing as a "hygrostat"?). I only need them to act on two states: 'sufficient' temp. and humidity, and 'insufficient.'

Coupled with these sensors will be a common space-heater and humidifier. I need to know how I can create an intermediary"on/off" switch to both of these 120V-A/C outlets. When the "insufficient" state of either condition arises I want to complete a circuit that will allow the heater/humidifier to run until the "sufficient" state has been acheived and then terminate the circuit.
I need to know if this is even possible in the far less cost- prohibitive analog realm. I could rig an overly-complicated DAQ-card based and software-driven constant-polling set-up for #1), but still would need help on the switching described in #2).

If anyone has an easy solution for me (and likes a good bottle of wine, which I would be happy to offer as remittance) I would greatly appreciative.

Thx all,

Luke

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John Fields 19 years ago

Yes, it can easily be done in hardware: A DC power supply, A temperature sensor, a humidity sensor, two comparators, two solid-state relays, and a handful of passive parts. Less than about $50 for parts, neglecting the enclosure.

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JeffM 19 years ago

The hubris of people on Usenet constanly amazes me

--people who think they have unique problems which havn't been solved a billion times before

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and which don't have off-the-shelf solutions.

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controllers

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Homer J Simpson 19 years ago

Yes. Honeywell and other companies sell them. You should try Home Depot for a start.

. . . . . . . .

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Fred Bartoli 19 years ago

He he, people which you are part of since there sure isn't a billion people, err... family, equipped with a wine cellar, not even counting their willingness to tightly control it :-)

Thanks, Fred.

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John 19 years ago

The simplest temperature control device would be a heater with a thermostat - 1000 watt heaters are available for $20US (maybe half that as they go on clearance - I just bought one at Lowe's for $10).

The next level of control is a line voltage thermostat which can handle the power required by the heater (less than 10 amps for a 1000 watt heater). These are often over $100US new, but are usually available on ebay for $25 - $50:

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You would need to mount the thermostat in a box with an adequate power cord (rated the same as the space heater cord) and an outlet for plugging in the heater.

Humidity controllers are not as readily available and most are designed to interface to a low voltage control system of some type. These need some eletrical/electronic interfacing to be able to control apower to a humidifier. Ebay is also a good source for these ($25US or less):

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Digital temperature sensors are inexpensive (DS18B20 ~$5US), as are low power microcontrollers (PICAXE 08M ~$4US). The code for a basic temperature controller is available on the web for free:

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(my site) A solid state relay adequate to control a space heater is expensive new but generally available in surplus for under $10US: (18A @ 240V)

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A microcontroller could monitor both temperature and humidity and control two solid state relays (heater, humidifier), plus provide a status display - either simple on/off LED's or an LCD display the shows current temperature & humidity plus on/off status of heater and humidifier and out-of-range alarm capability (temp more than 5 degrees from optimum, humidity more than 5 or 10% from optimum)..

Note that the microcontroller option allows mounting the temperature and humidity sensors at their optimum locations in the area.

The choice is yours - Yugo, Ford, Lexus, Mercedes. It all depends on where your needs and your budget meet ;-)

I can provide a plug-in solution of your choice in about 30 days (longer if you want a finished wood case).

John

[picaxe] at [jecarter] dot [com]

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Wine Cellar Controls: Simple analog control for Temperature and Humidity

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