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  1. #21
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    Re: how to design a thermostat without Microcontroller?

    Seriously - I would use a small MCU for this if you want accuracy and stability. I appreciate you are trying to avoid using one but the cost will probably be lower overall and there are many advantages such as combining the temperature control and motor controls.

    I would do it this way:
    Simple MCU (8-pin 16F683 comes to mind because it has PWM and ADC on board) reads a temperature sensor and produces a proportional PWM output to switch current through some 10W power resistors. That avoids the point source of heat and hysteresis problems and would be far more reliable than a flashing light bulb. Total cost would be very low and almost no electronics needed. It can also run on low voltage for extra safety.

    Brian,
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.


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  2. #22
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    Re: how to design a thermostat without Microcontroller?

    It's simple. believe! the incubator is a box which a 220V AC light bulb is embedded in as a heater and a thermostat controls it.no additional device or accuracy is needed!
    You got inputs from people who shared their experience on thermal control but you stay firm in your standpoint, so I wonder what else you are expecting before doing something based on the links and circuits provided so far. Fact to consider: You did not give any clues about the volumetric sizing and thermal capacity of the system, if there exists forced ventilation, etc...so many of the concerns may apply to a greater or lesser degree, but in any case, again, if you want a simple approach go ahead and give us some feedback on the mapped temperature excursion measured.

    the temperature should be in 36-37 degree
    By the way, just to register: The allowed temperature range for incubating eggs (you did not mention which animal specie, I guess chicken), is not that wide as you may suppose, something around 1 degree of variation above or below, significantly increases the mortality rate on the lot, so I am curious to know how a simple on/off control ( on a small box, as you said ) without using the plant model estimation nor the modulation of injected power could achieve such a narrow range. A plus tip: The larger the box size and smaller the power source, the lower the drift around the desired temperature.
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  3. #23
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    Re: how to design a thermostat without Microcontroller?

    Boy, talk about over-engineering. You would think the OP asked how to design an interstellar spacecraft from the responses here.
    1) get a temperature sensor.
    2) connect it to a comparator with hysteresis.
    3) connect the output of the comparator to a relay
    4)done


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