Coal stove door automatic opening remote control circuit

When cooking with a coal stove, you need to open the stove door in advance and wait until the fire is strong before using it. The following is an introduction to an automatic furnace door opening device, which can
automatically open the furnace door at regular intervals before the owner returns home, saving the user the time of opening the door and waiting for the fire to flourish.
    This device has a simple structure and easy material selection, and is suitable for imitation by the majority of users of honeycomb briquette stoves.
    Circuit working principle Figure 18-42 is the circuit principle circle of the coal stove automatic opening device. It is actually a voice controlled circuit coal stove. The timer
is turned on and controlled by the alarm clock ringtone. The main component of the circuit is a monostable circuit composed of VT2 and VT3. The working principle of the monostable circuit
is: after the power supply is turned on, the positive electrode of the power supply provides a large enough base bias current to VT3 through the resistor Rs, so that it is in a saturated conduction state
, and its collector potential is low, about 0.2V. about. At the same time, the collector potential of VT3 is divided by the resistor wind and R,
providing a lower base potential for the transistor vrz, making it in a cut-off state. If the input is triggered by an external signal, this state (VT2i cutoff, VT3
saturated) can be maintained forever, so it is called steady state. In the steady state, the collector potential of VT2 is very high, and the base potential of VT3 is very low.
One end of the capacitor G is connected to the collector of VT2, and the other end is connected to the base of VT3, so G is charged with a certain voltage. Sex is positive on the left and negative on the right.
    When the collector and emitter of VT2 are momentarily short-circuited with a wire, the collector potential of VT2 suddenly decreases, but the voltage of capacitor G cannot
suddenly change, so the base potential of VT3 also decreases, causing VT3 to turn off. . After VT3 is cut off, its collector potential immediately rises
. Since the base potential of VT2 is obtained by dividing the collector potential of VT3 through the resistor Rs, the base potential of VT2
also rises, so that VT2 is divided by The cutoff turns to saturation. As time goes by, the charge on G will be gradually
discharged through R5 and the e\:c pole of VTZ, and its right end potential, that is, the base potential of VT3, will gradually increase. When it rises to o. At about 6V, VT3 will begin to conduct, and its collector potential
will begin to decrease. After the wind and voltage are divided, the base potential of VT2 will also begin to decrease, VTZ will begin to exit saturation, and its collector potential will begin to
increase. Due to the coupling effect of G, the base potential of VT3 further increases, VT3 further conducts and escapes, and finally leads to its saturation, causing VT2
to cut off, that is, it returns to its original stable state. It can be seen that after the monostable circuit is triggered by an external signal (such as using a wire to momentarily short-circuit the c and
e poles of VT2:), it can quickly flip from the steady state to another temporary stable state. After a period of delay, the cross will return to its original
steady state.
    The ringtone of the alarm clock is picked up by the microphone BM. Usually, the internal impedance of the microphone is relatively large, the collector potential of VT1 is high, and the monostable
circuit is also in a stable state. At this time, the collector potential of VT3 is very low. VT4 is in cut-off state and the relay does not close. When the microphone
senses a strong ringing sound, the internal impedance decreases sharply. This change makes C. The potential at the left end rises rapidly, which is equivalent to
inputting a positive pulse to the base of transistor VT1 , causing the base potential of VTI to rise rapidly and its collector potential to fall rapidly. This voltage change
is transmitted to the collector of VT2 through capacitor c2, causing the collector potential of VT2 to drop rapidly (equivalent to shorting the c pole to the e pole of VT2). As a result, the monostable
circuit produces the above-mentioned flipping change, causing the circuit to immediately turn into a temporary stable state. At this time, the collector potential of VT3 suddenly rises, causing VT4
to be saturated. Then the relay operates, K closes, the electromagnet is energized and operates, which triggers the mechanism set on the furnace door, causing the furnace door
to open under the tension of the spring.