Make a Timed Constant Temperature Lunch Box

Although the ordinary cooking lunch box is simple to use and operate but has a single function, it is not possible to set the time or set the temperature to heat. In order to improve this shortcoming, this time DIY is made on the basis of the cooking lunch box to make a timed constant temperature lunch box with regular heating and constant temperature insulation.

Step 1: Material Tool Preparation

1, cooking lunch box 1

2, timing thermostat controller 1 set

3, wire tools, etc.

Step 2: Power Input

The power input of the cooking lunch box is ~220V three-wire socket

Step 3: Unscrew the Four Fixing Screws and Open the Housing

The power-on detection function of the prepared cooking lunch box is normal, and the buttons and indicators are normal.

The bottom of the box has nameplate information; the power is 250W, the input power voltage is 50Hz AC 220V and its capacity is 1.2L.

Remove the four silicone feet on the bottom to see the cross-shaped fixing screws under the footpads. Unscrew the four fixing screws to open the case

Step 4: Opening With a Digital Tube

According to the position of the component after soldering, the position and size of the opening need to be drawn with a pen, and then the digital tube opening is completed.

Step 5: Installing Digital Tube

Then, the four-hole positions of the button are also opened, and the digital tube button module can be installed

Step 6: Connect Module

Install the control board into the cut groove and connect each module to the control board

Step 7: Glue Fixing

Plus hot melt adhesive for fixing

Step 8: Add Glue

Hot melt adhesive is also added around the digital tube

Step 9: Add High Temperature Tape

Use a thermal adhesive to adhere the thermistor to the PTC heating aluminum plate, then cover the entire thermistor with high-temperature tape to prevent it from falling off.

Step 10: Add High Temperature Tape

Solder and fix the position of the buzzer, and finally add a layer of high-temperature tape to the heat-shrinkable tube

Step 11: Close the Lid

Cover it and everything is done

Step 12: Finished Product Appreciation

Timing heating time mode setting, current setting countdown heating time 05:30

Step 13: Constant Temperature Mode

Constant temperature setting mode display: 80 ° C

Step 14: Design Principle （Principle Diagram Before Transformation）

principle

There are two main functions added to the DIY timed constant temperature lunch box. The first one is the timing function: the heating time can be set. When the set time arrives, the heating will stop. The second one is the constant temperature insulation function. After the constant temperature is set, the temperature in the lunch box will be kept constant and set. temperature:

First, draw the schematic diagram of the original cooking lunch box, and then add a timed thermostat controller to achieve the function according to the requirements:

Step 15: Design Principle（Tafter the Transformation）

On the basis of the original, adding a timed thermostat controller, the main control is the opening of the PTC to control the temperature.

Step 16: Design Principle （Timing Thermostat）

The main controlchipof the control panel of the timed constant temperature lunch box is STM8S103. The temperature measuring component is: NTC single-ended glass sealed thermistor. The specifications of the switching power supply conversion module are input ~220V, output +5V 700mA. Active buzzer, digital tube, touch button, and universal board. 5V controlled relay, the maximum current can pass 250V3A, the current margin is enough.