How to make a reliable thermostat for household needs

I recently got an incubator. But due to its cheapness, the temperature controller in it broke down. Therefore, I decided to assemble a simple and reliable thermostat with my own hands.

The device is designed for automatic control of heating or cooling equipment in domestic conditions. Maintains temperature at the level specified by the user.

Diagram and details

Temperature adjustment within 20-90 degrees Celsius.

Parts with the following ratings:

• R1,R5,R6-2.7 kOhm, R3-10 kOhm, R4-43 kOhm - http://alii.pub/63abmx
• R2-NTC thermistor 10 kOhm - http://alii.pub/63abo3
• C1-100 µF, C2-100 nF - http://alii.pub/5n14g8
• VT1 is any low-power npn transistor. In my case it is 2n2222.
• MC1 is a comparator. I have this microcircuit LM358 - http://ali.pub/5jqqeg, but you can put any other comparator here (LM 2904, LM324, LM393). You will only need to change the printed circuit board.
• VD1 is any low-power diode - http://alii.pub/5m5na6
• And relay REL1 should be 12 V - http://alii.pub/60ep1w
• LEDs any - http://alii.pub/5lag4f

I would like to note that it is better to use a new variable resistor, since the coating of the old one may be erased and the thermostat adjustment will occur in jerks.

Making a thermostat with your own hands

The signet was found on the Internet, but modified to suit my needs. In particular, I removed the relay from the board. I made the board using LUT and etched it with a solution of hydrogen peroxide.

Afterwards, I soldered all the elements. This is what the original version looks like. In the future it was changed due to incorrect operation of the circuit.

The body of the product was made from a broken modem.

For power supply I used a 5-pin DIN male connector.

To quickly replace the sensor, I also used this connector (if it was broken or if a thermistor for a different resistance was needed).

To make it even more beautiful, I decided to try for the first time to make a “cover” for the front panel. It is made of paper covered with tape. The drawing was drawn in the board tracing program Sprint-Layout 6.0.

The temperature scale will be added by hand.

This is what the device looks like in the final assembly. To connect the controlled load, I brought out the wires and used WAGO connectors.

Watch the video

This circuit has a sufficiently high accuracy for domestic needs. The cost of the thermostat is around 150 rubles. for March 2022.