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The circuit that I present to you has the function of controlling the temperature of any appliance that uses an electric heater, such as a fish tank, a home heater, an electric stove, etc. It works with 50 or 60 hertz and 100 to 250 Vac

Fish tank Temperature control. Caution this device handles line voltages. Improper handling can cause electric shocks that could cause damage or even death, I recommend keeping the elements that touch water very well insulated, taking into account the capillary property of water. The circuit that I present to you has the function of controlling the temperature of any appliance that uses an electric heater, such as a fish tank, a home heater, an electric stove, etc. It has the advantage that the control is gradual and does not generate sudden changes in temperature, as happens with heaters that use bimetallic elements. The device has two modes of operation, preselected with a removable jumper (JP3): Mode 1.- the removable jumper installed, closed circuit, in this mode the TRIAC firing angle is proportional to the position of the potentiometer (R9), without taking into account the reading of the thermistor (RT1), also called open loop control . 
Mode 2. - the jumper removed, open circuit, in this mode when setting the desired level with the potentiometer, the thermistor reading will try to match the position of the potentiometer, it should be mentioned that this depends on the physical position of the heater and thermistor and the temperature propagation medium, this mode is also called closed loop control or feedback control.
 
Its operation is based mainly on controlling, by means of a micro controller, the firing angle of a TRIAC. To achieve this micro controller needs to know or calculate the following:
 
1. - Power supply for the micro controller and its components

2. - The exact moment when the AC line changes from negative to positive and vice versa called the zero crossing detector.

3. - The frequency of the line
4. - The position of the potentiometer that establishes the desired temperature.
5. - The measurement of the temperature of what is being controlled.


I apologize for the delay in completing the project as soon as it is ready I will upload it for you