[Electronics] DIY makes a timed constant temperature lunch box

I have dismantled an ordinary electric cooking lunch box. Although the ordinary cooking lunch box is simple to use and operate, but has a single function, it cannot 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.

So how do DIY make a regular temperature lunch box?

P01 timed constant temperature lunch box

First, preparation for production

Rendering

The time and temperature display of the timed constant temperature lunch box is realized by a 4-digit digital tube. In addition, 4 buttons are designed to realize the corresponding parameter setting and function selection:

P02 finished product renderings

Material tool preparation

1, cooking lunch box 1

2, timing thermostat 1 set

3, wire tools, etc.

P03 DIY protagonist

Second, the design principle

1, the principle

The DIY regular temperature lunch box mainly adds two functions. The first one is the timing function: the heating time can be set. When the setting 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. 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:

P04 principle diagram before transformation

On the basis of the original, the timing constant temperature controller is added, and the main control is the opening of the PTC to control the temperature:

P05 modified after the timing of the constant temperature lunch box principle icon

The main control chip of 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. The 5V controlled relay can pass up to 250V3A current, and the current margin is enough:

P06 timing thermostat controller

Third, DIY process sharing

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

P07 power plug

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 supply 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 foot pads. Unscrew the four fixing screws to open the case:

P08 open the interior

According to the position of the component after soldering, use the pen to trace the position and size of the hole, and then complete the digital tube opening:

P09 digital tube mounting hole

Then, the four holes of the button are also opened, and the digital tube button module can be installed:

P10 Install the digital tube button

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

P11 connection module

Plus hot melt adhesive for fixing:

P12 glued and fixed

Hot melt adhesive is also added around the digital tube:

P13 gluing

Use a thermal paste to attach the thermistor to the PTC heating aluminum plate, then cover the entire thermistor with high temperature tape to prevent it from falling off:

P14 glued to 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:

P15 plus high temperature tape

Close the lid and you're done:

P16 cover

Fourth, the finished product appreciation

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

P17 timing mode

Constant temperature setting mode display: 80 ° C:

P18 constant temperature mode

Finish the production!

Five, there is something to say

The final effect of the DIY production of the regular temperature lunch box is very good, and it is more advantageous than the single function of the cooking lunch box at the beginning, and the application is more extensive.

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