Disassembling an unknown thermostat

wudianjun2001

Disassembling an unknown thermostat [Copy link]

Yesterday my boss gave me a thermostat and asked me to take it apart to see how it works. After taking it apart, I found some of the parts quite interesting, so I posted this to share with you, which is also a way to save information for myself. This thermostat is powered by two AA batteries.

When I first got it, I thought it was a mechanical thermostat because it didn't have a display screen or buttons like an electronic thermostat. It did have the common dials and dials of a mechanical thermostat. Later I realized I was wrong.

Let's take a look at the appearance of the thermostat. It may be a pirated product exhibited at the exhibition, so the manufacturer's LOGO in the upper right corner has been wiped off. There are several dials and a dial code on the front of the thermostat. From the icons above, we can guess that the large dial above is used to set the daytime and nighttime. This dial is very interesting and will be explained in detail later. The two dials above, one is for setting the daytime temperature, ranging from 10-30 degrees, and the other is for setting the night temperature, ranging from 10-26 degrees. A dial selects shutdown, timer control and manual control. There is also a battery undervoltage indicator.

Next, we will disassemble the thermostat. There are two clips at the bottom of the thermostat, which can be opened by prying with a screwdriver. It is very convenient to install.

The top cover is the main part of the thermostat. The upper part is a circuit board, which is powered by the battery. The temperature dial is installed on it, as well as the output pins of the relay. Below is a 24-hour setting dial.

The rear cover is mainly a wiring terminal, which is also a common terminal and normally open and normally closed contacts of a relay output. There is a plastic terminal shell for protection. You can connect the wires after removing the screws. This protection is very necessary, because when installing, you first remove the rear cover, fix the rear cover on the 86 installation box, and then connect the wires. After completion, cover the front cover.

Continue to remove the things on the cover, first remove the turntable to see what it is. This is a whole, look at the printing on it, 1,2 pins are power input 1.4-1.6V DC, below is a switch. Baidu didn't find any information on the specific model.

The disassembled turntable has many dials on it, which I call them by myself, corresponding to the 24 hours of a day. The turntable can rotate clockwise, but not counterclockwise. Any dial on it can fluctuate, and can fluctuate to the middle or outside. The rotation of the turntable can be used to set the current time, and the black triangle points to the current time. The dial can be used to set the time period, for example, 1-3 o'clock and 8-15 o'clock correspond to the daytime temperature value, and the others correspond to the nighttime temperature value. You can set any time period, but there are only two temperature values for the time period, one that fluctuates to the middle and one that is dialed to the outside.

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Combined with the above, we can guess that there is a motor in this dial, which can drive the turntable to rotate, just for timing. The speed and deceleration of the motor are calculated to be exactly equal to the time, so as to achieve accurate timing. Let's continue to disassemble this thing. There are 4 buckles around it, just pry it open. But when I pried it open, it was bad, the gears fell off, and I didn't know where they were.

Just take down all the gears, and the small circuit board as well.

There is a bound cow dung block and a 32K crystal oscillator on this circuit board. There are 6 wires coming out of the bound block, two for power input, two for crystal oscillators, and two for driving a coil. This coil is also quite interesting, it is actually a motor. There is a black gear in the middle of the iron block on the right, and the bottom of this gear is magnetic. Through the change of the direction of the coil current, the iron block generates a magnetic field, which causes the gear to rotate. I guess, when I powered on later, I found that the turntable did not work, maybe the motor part was broken. There is also a micro switch on this board, and later it was found that a transmission part was connected to it. The dial of the large turntable is turned to the middle and outside, which can be detected by this micro switch.

Let's restore this big dial. The position of the gears is just by guessing. Generally, different positions are fixed. Some gears have holes in the middle, and some have steps at one end. Then, according to the meshing condition of the gears, it can be restored after a few tries.

After looking at the large dial above, let's take a look at the circuit board on the upper cover. After removing it, I have never seen the model of MCU before, and I have not found any information. I don't care. There is a SOT23-5 thing near the pin. It is a power chip that converts the battery voltage into 1.5V to supply power to the time dial. The two blue potentiometers correspond to the daytime and nighttime time settings. The relay uses a magnetic latching relay. One advantage of this relay is that it saves power. It only needs to be powered off when it is in action. It is driven by the H-bridge circuit of 4 transistors. The orange thing in the upper right corner should be a thermistor, collecting room temperature. The lower left corner is a dip switch, which is for electronics. This circuit board is relatively simple.

After disassembling and playing with it, I reassembled it and powered it on for testing. There was no problem with the relay action, but the time dial below would not rotate by itself. It is estimated that there is a problem with the motor drive part inside. Everything else is normal. That's all I have to say.

Everyone is welcome to discuss and point out areas where you don't understand enough.

0pt]Just take down all the gears, and the small circuit board as well

There is a bound cow dung block on this circuit board, and a 32K crystal oscillator. The binding block has 6 wires, two power inputs, two crystal oscillators, and two drive coils. This coil is also quite interesting, it is actually a motor. There is a black gear in the middle of the iron block on the right, and the bottom of this gear is magnetic. The change in the direction of the coil current generates a magnetic field, which causes the gear to rotate. I guessed that when I powered on the power later, I found that the turntable did not move. It might be that the motor was broken. There is also a micro switch on this board. Later, I found that a transmission part was connected to it. The micro switch can detect when the dial of the large turntable is moved to the middle and outside.