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  1. #61
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    Re: how to design a thermostat without Microcontroller?

    to introduce 0.5C hysteresis, what are the value of the voltage divider's resistors?
    It seems that you are not paying attention to the remarks provided so far. Re-read the posts from the beggining, and you will realize that it is not possible to achieve a theoretical performance without having sufficient data from the system. As already mentioned more than once, there is an intrinsic error expected on the control system due to the mass (thermal capacity and material used) of the object to be measured. Time to start making experiments by yourself to better understand what people are meaning.
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    Re: how to design a thermostat without Microcontroller?

    Quote Originally Posted by c_mitra View Post

    You have another free opamp on the same IC; use the spare one to make one unity gain inverting buffer and again use another 0.01uF capacitor as a high pass filter. That can be used to drive the transistor.

    Use another 0.1uF capacitor in parallel with the diode across the relay coil. That may help the regulator from voltage spikes.
    your indescribable concerns & kindnesses will not be forgotten.

    but another question still remains. what is the use of this free OP-AMP? How it should be connected?
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    Re: how to design a thermostat without Microcontroller?

    Hi,

    You don't show any effort on your own.
    Not even the simplest internet search for "unity gain inverting opamp".

    I don't support laziness.
    I'm back when I see you do your job ...

    Klaus
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    Re: how to design a thermostat without Microcontroller?

    but another question still remains. what is the use of this free OP-AMP? How it should be connected?
    You need three more 10K (or 100K) resistors; add one to the non-inverting input (other end goes to ground). Add another to the inverting input and the output. This output is connected to the transistor driving the relay.

    Connect the third resistor between the output of the first op-amp and the inverting input of the second op-amp.

    Can you please draw a fresh circuit and post that?



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    Re: how to design a thermostat without Microcontroller?

    @Dr_Mohammad
    Reviewing this extense thread it is clear that from now on it is possible to you go ahead with all the detailed information given so far. As said, it is expected some background on electronics to seek for elementary information widely available on the Web. Here and at all other forums it is not usual to ask commonplace questions, therefore we'll be glad to reopen this thread when you show results of your experiments and/or ask for questions due issues arising from it.
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