A very simple egg incubator temperature controller thermostat circuit using LM 35 IC is explained in this article. Let's learn more.
How Incubators Work
An Incubator is a system where bird/reptile eggs are hatched through artificial methods by creating a temperature controlled environment. Here the temperature is precisely optimized to match the natural incubating temperature level of eggs, which becomes the most crucial part of the whole system.
The advantage of artificial incubation is faster and healthier production of the chicks compared to the natural process.
Importance of Temperature Controlled Environment
Anybody involved in this profession will understand the importance of a temperature controller circuit which should be not only reasonably priced but also have features like precise temperature control and manually adjustable ranges, otherwise the incubation could get hugely affected, destroying most the eggs or developing premature offspring.
I have already discussed an easy to build incubator thermostat circuit in one of my earlier posts, here we'll learn a couple of incubator systems having easier and much more user friendly setting up procedures.
The first design shown below uses an opamp and a LM35 IC based thermostat circuit and indeed this looks quite interesting due to its very simple configuration:
Temperature Indicator Circuit using IC 741 and LM35 IC
The idea presented above looks self explanatory, wherein the IC 741 is configured as a comparator
with its inverting pin#2 input pin is rigged with an adjustable reference potentiometer while the other non-inverting pin#3 is attached with output of temperature sensor IC LM35
The reference pot is used to set the temperature threshold at which the opamp output is supposed to go high. It implies that as soon as the temperature around the LM35 goes higher than the desired threshold level, its output voltage becomes high enough to cause pin#3 of the opamp to go over the voltage at pin#2 as set by the pot. This in turn causes the output of the opamp to go high. The outcome is indicated by the lower RED LED which now illuminates while the green LED shuts off.
Now this outcome can be easily integrated with a transistor relay driver stage for switching the heat source ON/OFF in response to the above triggers for regulating the incubator temperature.
A standard relay driver can be seen below, wherein the base of the transistor may be connected with pin#6 of the opamp 741 for the required incubator temperature control.
The Relay Driver Stage for Switching the Heater Element
Incubator Temperature Controller Thermostat with LED Indicator
In the next design we see another cool incubator temperature controller thermostat circuit using an LED driver IC LM3915
In this design the IC LM3915 is configured as a temperature indicator through 10 sequential LEDs and also the same pinouts are used for initiating the ON/OFF switching of the incubator heater device for the intended incubator temperature control.
Here R2 is installed in the form of a pot and it constitutes the threshold level adjustment control knob and is used for setting up the temperature switching operations as per the desired specifications.
The temperature sensor IC LM35 can seen attached to the input pin#5 of the IC LM3915. With rise in temperature around the IC LM35 the LEDs begin sequencing from pin#1 towards pin#10.
Let's assume, at room temperature the LED#1 illuminates and at the higher cut-off temperature the LED#15 illuminates as the sequence progresses.
It implies that pin#15 may be considered the threshold pinout after which the temperature could be unsafe for the incubation.
The relay cut-off integration is implemented according to the above consideration and we can see that the base of the transistor is able to get its biasing feed only upto pin#15.
Therefore as long as the IC sequence is within pin#15, the relay remains triggered and the heater device is held switched ON, however as soon as the sequence crosses over pin#15 and lands on pin#14, pin#13 etc. the transistor biasing feed is cut off and the relay is reverted towards the N/C position, subsequently switching OFF the heater..... until temperature normalizes and the sequence restores back below the pin#15 pinout.
The above sequential up/down drift keeps on repeating in accordance with the surrounding temperature and the heater element is switched ON/OFF maintaining almost a constant incubator temperature as per the given specifications.