Instantaneous water heater automatic constant temperature experiment circuit diagram

　　I have used an instant water heater at home for many years, but I have troubles every time I take a bath. The water temperature control of the water heater is divided into 9 levels, from 1 to 9, the higher the number, the higher the temperature. It should be easy to use. However, the water flow rate can also dominate the water temperature, and often cause the temperature to get out of control. For example, when the water pressure decreases and the water volume decreases, the heat cannot be taken away by the water immediately, and the temperature (protection) switch inside the water heater will be controlled. You will be scalded for a while and then tortured by cold water, which is very uncomfortable.

　　In order to change this situation, I added a simple temperature control circuit which can control the heating time, that is, the duty cycle, of the original circuit. The effect is satisfactory, especially the temperature (protection) switch inside the water heater has never been activated again, which is very comfortable.

　　The temperature sensor in the circuit uses an old-fashioned thermistor. Since its resistance is a bit small, a germanium diode is added.

　　The main components used in the water heater circuit are: ULN2003AN, 7805/7812, BTA41600B, JQX-15F, HMS87C1202A, MOC3021