Automatic egg incubator

How the Circuit Works

The automatic egg incubator circuit consists of a power supply circuit, a temperature/ventilation control circuit, an automatic egg turning circuit and a temperature indication circuit, as shown in Figure 1.

The power supply circuit consists of a power switch S3, a power transformer T, a rectifier bridge UR and capacitors C2-C4, a current limiting resistor R12 and a voltage regulator diode VS.

The temperature/ventilation control circuit is composed of transistors V1, V2, resistors R1-R11, potentiometers RP1-RP5, operational amplifier integrated circuit 1C1 (N1-N3), relay K1, diode VD1, fan motor M1 and heater EH. Among them, V1, C1, R1-R6, RP1, R and N1 inside IC1 form the temperature detection control circuit; R7, R10, R11, RP3, N3 inside IC1, V2 and VD1 form the drive control circuit of K1; resistors R8, Rg, RP4, RP5 and N2 inside IC1 form the buffer amplifier circuit.

The automatic egg-turning circuit is composed of resistors R13-R16, potentiometer RP6, capacitors C7-C9, time-base integrated circuit IC2, transistor V3, diode VD2, relay K2, limit switch S1, trigger switch and DC motor M2. Among them, IC2 and peripheral resistors and capacitors form an astable circuit; V3 and R13, R14, VD2, K2 and S1 form the control circuit of M2.

When the power switch S3 is turned on, the AC 220V voltage is stepped down by T, rectified by UR, and filtered by C3 and C4 to generate a +9V working voltage, which is supplied to the drive control circuit, buffer amplifier circuit and automatic egg-turning circuit of K1. The +9V voltage is also stepped down by R12, filtered by C2 and stabilized by VS to provide a +5V working voltage for the temperature detection control circuit.

V1 is used as a temperature sensor to detect the temperature in the incubator. The voltage of its emitter junction (between the b and e poles) decreases as the temperature rises (temperature coefficient is -2mV/℃). RP4 is used to set the control temperature.

When the ambient temperature in the incubator is lower than the set control temperature of R, amplifiers N1 and N3 output high level, making V2 saturated and conducting, K1 energized and attracted, its normally open contact connected, fan motor M1 and heater EH energized and working. When the ambient temperature in the incubator exceeds the set control temperature, amplifiers N1 and N3 both output low level, making V2 cut off, K1 released, its normally open contact disconnected, fan motor M1 and heater EH stop working. This process repeats itself, making the temperature in the incubator constant at the set temperature.

At the moment of power on, since the voltage across C7 cannot change suddenly, the 2nd and 6th pins of IC2 are at low level, the 3rd pin outputs high level, V3 is cut off, m is in the released state, and M2 does not work. Then C7 is charged through R16, RP6 and R15, so that the potential of the 2nd and 6th pins of IC2 gradually rises. When the voltage across C7 is charged to more than 6V (about 2h), the circuit in IC2 flips, the 3rd pin becomes low level, V3 is turned on, m is energized and attracted, and its normally open contact is connected, so that M2 is energized and rotated, and the hatching tray with the hatching eggs is tilted in one direction through the deceleration and traction device to complete the egg turning action.

When the hatching tray is tilted to a certain angle (about 70°), the trigger mechanism installed on the deceleration traction wheel turns on the normally open contact of S1 and disconnects the normally closed contact, changing the polarity of the power supply applied to M2. At the same time, the trigger turns on for a moment, making the discharge output circuit inside the 7th pin of IC2 work, and C7 discharges quickly. When the voltage across C7 is lower than 3V, the 3rd pin of 1C2 becomes high level, making V3 cut off, K2 released, and its normally open contact disconnected, so that M2 stops rotating. Then C7 is slowly charged through R16, RP6 and R15. When the voltage across C7 is charged to more than 6V, the circuit inside IC2 turns over again, and the 3rd pin outputs a low level, so that V3 is turned on, the burning electricity is attracted, and its normally open contact is turned on, so that M2 is powered on and rotates. Through the deceleration and traction device, the hatching tray with the hatching eggs is tilted in the opposite direction, completing the egg turning action.

When the hatching plate is tilted to a certain angle, the trigger mechanism installed on the deceleration traction wheel disconnects the normally open contact of S1 and connects the normally closed contact, changing the polarity of the power supply applied to M2. At the same time, S4 is triggered and connected, making the discharge output circuit inside the 7th pin of IC2 work, and C7 discharges quickly. When the voltage across C7 is lower than 3V, the 3rd pin of IC2 becomes a high level, cutting off V3 and releasing K2, and its normally open contact disconnects, causing M2 to stop rotating again.

The above working process is repeated over and over again, and the eggs can be automatically turned over once every 2 hours.

By adjusting the resistance values ​​of RP1 and RP2, the slope of the voltage on the emitter junction of V1 changing with temperature can be changed.

By adjusting the resistance values ​​of RP3 and RP5, the accuracy of the displayed temperature can be adjusted.

By adjusting the resistance value of RP6, the time of automatic egg turning can be changed.

The digital temperature display panel is used to display the temperature in the incubator and the set temperature. When the temperature display conversion switch S2 is set to position A, it is used to display the temperature in the incubator; when the temperature display conversion switch S2 is set to position B, it is used to display the set control temperature.

Component Selection

R1-R17 all use 1/4W carbon film resistors or metal film resistors.
RP1-RP5 use high-quality synthetic film potentiometers or multi-turn potentiometers; RP6 uses organic solid potentiometers.
C1, C4-C6 and C8 all use monolithic capacitors; C2, C3 and C7 all use electrolytic capacitors with a withstand voltage of 16V; C9 uses two 470μF, 10V aluminum electrolytic capacitors in series (the positive poles of the two capacitors are connected in series).
VD1 and VD2 all use 1N4007 silicon rectifier diodes.
VS uses a 1/2W, 5V Zener diode.
V1 uses a 3DG6 silicon NPN transistor; V2 uses an S9013, C8050 or 3DG12 NPN transistor; V3 uses a C8550 or 3CG8550 PNP transistor.
UR uses a 1-2A, 5OV rectifier bridge stack.
IC1 uses 1M324 operational amplifier integrated circuit; IC2 uses NE555 time base integrated circuit.
K1 and K2 use KKR-13F 9V DC relay.
M1 uses 2OW small fan motor (can be installed near the air hole at the bottom of the incubator when in use); M2 uses 9V DC reduction motor.
EH can be reasonably selected according to the volume of the incubator.
S1 uses a bipolar two-position micro switch; 52 uses a single-pole two-position conversion switch; 53 uses a 10A, 220V power switch; S4 uses a high-sensitivity micro switch.