Sunday, December 25, 2011

How to Build a Simple Egg Incubator Thermostat Circuit

An electronic incubator thermostat circuit shown in this article is not only simple to build but is also easy to set and acquire exact tripping points at various different set temperature levels. The setting may be completed through two discrete variable resistors. The sensing range is quite good from 0 to 110 degrees Celsius.
Switching a particular load at different threshold temperature levels doesn’t necessarily need complex configurations to be involved in an electronic circuit. Here we discuss a simple construction procedure of an electronic incubator thermostat.
This simple electronic incubator thermostat will very faithfully sense and activate the output relay at different set temperature levels from 0 to 110 degree Celsius.

The conventional electromechanical temperature sensors or thermostats are not very efficient due to the simple reason that they cannot be optimized with accurate trip points.
Normally these types of temperature sensor or thermostats fundamentally use the ubiquitous bimetal strip for the actual tripping operations. When the temperature to be sensed reaches the threshold point of this metal, it bends and buckles.

Since the electricity to the heating device passes through this metal, it’s buckling causes the contact to break and thus power to the heating element is interrupted - the heater is switched off and the temperature starts falling. As the temperature cools, the bimetal starts straightening to its original form. The moment it reaches its previous shape, the electricity supply to the heater is restored through its contacts and the cycle repeats.

However, the transition points between the switching are too long and not consistent and therefore not reliable for accurate operations.

The circuit presented here is absolutely free from these drawbacks and will produce comparatively high degree of accuracy as far the upper and the lower tripping operations are concerned.




Parts List

R1 = 2k7,
R2, R5, R6 = 1K
R3, R4 = 10K,
D1---D4 = 1N4007,
D5, D6 = 1N4148,
P1 = 100K,
VR1 = 200 Ohms, 1Watt,
C1 = 1000uF/25V,
T1 = BC547,
T2 = BC557,
IC = 741,
OPTO = LED/LDR Combo.
Relay = 12 V, 400 Ohm, SPDT.

Circuit Description

We know that every semiconductor electronic component changes its electrical conductivity in response to the varying ambient temperature. This property is exploited here to make the circuit work as a temperature sensor and controller.

Diode D5 and transistor T1 together form a differential temperature sensor and interact greatly with each other with changes in the respective surrounding temperature.

Also since D5 acts as the reference source by staying at the ambient temperature level should be kept as far as possible from T1 and in open air.

Pot VR1 may be used externally to optimize the reference level set naturally by D5.
Now assuming D5 is at a relatively fixed temperature level (ambient), if the temperature in question around T1 starts rising, after a particular threshold level as set by VR1, T1 will begin to saturate and gradually start conducting.

Once it reaches the forward voltage drop of the LED inside the opto-coupler, it will start glowing correspondingly brighter as the above temperature rises.
Interestingly as the LED light reaches a particular level, further set by P1, IC1 picks this up and instantly switches its output.

T2 along with relay also respond to the IC’s command and respectively actuate to trip off the load or the heat source in question.

How to Make an LED/LDR Opto-Coupler?


Making a homemade LED/LDR opto is actually very simple. Cut a piece of general purpose board about 1 by 1 inch.
Bend the LDR leads near its “head.” Also take a green RED LED, bend it just as the LDR (See figure and Click to Enlarge).

Insert them over the PCB so that the LED lens point is touching the LDR sensing surface and are face to face.
Solder their leads at the track side of the PCB; do not cut off the remaining excess lead portion.
Cover the top with an opaque lid and make sure its light proof. Preferably seal off the edges with some opaque sealing glue.

Let it dry. Your home made LED/LDR based opto-coupler is ready and may be fixed over the main circuit board with its leads orientations done as per the electronic incubator thermostat circuit schematic.

Update:

After some careful investigation it became evident that the above opto-coupler can be totally avoided from the proposed incubator controller circuit.

Here are the modifications which needs to be made after eliminating the opto.

R2 now directly connects with the collector of T1.

The junction of pin#2 of IC1 and P1 hooks up with the above R2/T1 junction.

That's it, the simpler version is now all ready, much improved and easier to handle.

Please check-out the much simplified version of the above circuit:



114 comments:

  1. Hai.
    I just want to get some information about the circuit which you have given here.You didn't mentioned about the transformer TR1 in the parts list.

    ReplyDelete
    Replies
    1. Hi Thomas,

      The transformer is 0-12V/500mA.

      Thanks!

      Delete
  2. Thanks for this also but the motor if DC (12V) should be powered from the DC supply??

    ReplyDelete
  3. How could you power this circuit using DC?

    ReplyDelete
    Replies
    1. Eliminate TR1, D1--D4 and apply the DC across C1....

      Delete
    2. Thank you for your help. This is an awesome blog keep up the good work.

      Delete
  4. Hi. The Led of the Opto-coupler is a RED or a Green one?

    ReplyDelete
  5. Hi,
    Will this work on uk 240v ac?

    ReplyDelete
  6. Do you mean R1=27K or something else.Please answer

    ReplyDelete
  7. hi..what is the main output of this circut,whether to make constant temperature at output or to switch the heater just on and off...

    ReplyDelete
    Replies
    1. To switch the heater ON and OFF with respect to the ambient temperature....as the ambient temperature increases the heater is kept switched OFF for longer periods of time and vice versa.

      Delete
  8. i need to know the clear functionality of this circuit so that it can be helpful for my miniproject which i have to submit by this weekend..please mail me clear description of it..muralidhar271220@gmail.com

    ReplyDelete
    Replies
    1. The functioning has been explained elaborately in the article...

      Delete
  9. sir plz post this circuit PCB diagram pic

    ReplyDelete
  10. sir plz post this circuit PCB diagram

    ReplyDelete
  11. sir,i would like to do a mini project on this topic and i would like to know hw to set the temperature to a 35-38 degree celsius used in neonatal incubators.pls rply fast....
    thank u

    ReplyDelete
    Replies
    1. You can do it by adjusting P1 as shown in the circuit.........

      Delete
  12. sir, you are a very talented guy when it comes to electronics but i got a lil problem with regards to my project to pass for my accelerated electronics course. how can i possibly wired this these three and lay out it in pcb hence im no whiz on electronics:

    water circuit level a controlfor humidity
    heater sensor to heat the incubator
    motor timer to turn the eggs 4 times aday
    if you could hel me howto get this work it would be an honor
    ty

    ReplyDelete
    Replies
    1. Thank you very much!

      A simple Incubator heater sensor circuit is given in the above article, so you can try the shown circuit.

      I'll try to design your other needs soon, and post it in my blog.

      Stay in touch.

      Delete
    2. dear swagatam,\
      thanks for the reply and for your concern actually rigth after i sent you a message i design it already and put to pdf file for printing in one paper the (three circuit boards)i run drc test on each board it passes but some pins are not connected due to im no whiz in finding the rigth ic's on my software it's quite hard but im enjoying plotting drawings...
      by way im using a microcad for pcb layout.
      thanks and happy new year

      Delete
    3. OK that's great!!

      Wish you too, a happy 2013!!

      Delete
  13. Good day Sir Swagatam, do you have a PCB layout for this incubator project? I am currently downloading the orcad software for me to make the pcb layout of this but takes a day i think for me to wait for the download to finish. your blog really helps a lot of people especially ECE students. Good job. can i have a copy of your pcb layout please sir, you can email me at dave_harry22@yahoo.com... Thank you so much sir

    ReplyDelete
    Replies
    1. Gooday and Thank you Randolph,

      As you know designing a PCB is a hugely time consuming task, so presently it would be difficult for me to design it, but I'll try to update it in my free time soon.

      Delete
  14. SIR i have a question . What is the IC 1 Value?

    is it an OP AMP?


    ReplyDelete
  15. thank you very much sir Swagatam!!! i just realized my mistakE!

    actually, I just committed a "PERSONAL ERROR" of "printing out your design" leaving the "IC = 741" uncopied!!

    Sorry for this mistaken question! :D hahaha

    By-the-way... i still have another question sir,

    1.) SInce P1 is also a variable Resistor.. which has 10k,
    Do i need to consider its Wattage???

    2.) is P1 the adjustable part? or VR1?



    TY PLEASE KEEP THIS UP! :thumbsup:

    ReplyDelete
    Replies
    1. No problem Jifty!

      Actually Both P1 and VR1 are presets, just the names are differently assigned, wattage is not important, you may use any normal type.

      Thanks!

      Delete
  16. i really have problem on my circuit, is there any alternative on what to use as replacement for 200ohms potentiometer as variable resistor? my circuit isnt working since i used 2k ohms potentiometer as VR.

    ReplyDelete
    Replies
    1. try making a potential divider network by joining 56 ohm/100 ohm resistors, the free end of 56 ohm goes to R1, the free end of 100 ohms goes to ground, the center joint goes to the base of bc547.....hopefully this might work in place of the pot

      Delete
  17. Hello Swagatam
    Please i want to build this cercuit for an incubator but i don't understand how D5 1N4148 and T1 BC547 measures the temperature. the datasheets for this two components does not talk about how they react on temperature.
    please explain it to me.
    Best regards,
    Giniti

    ReplyDelete
    Replies
    1. Hello Giniti,

      The datasheet of all semiconductor mention one of the characteristics (power dissipation typically)) with reference to ambient temperature, referred to as Tamb(oC), which indicates that these components vary their power output in response to ambient temperature.

      Delete
  18. Hello Swagatam,
    I did build the circuit without TR1 D1,2,3,4 and C1, finaly i wanted to test it bij using an external power of 12v DC. By mistake i connected the power wrong (12v becomes the mass) and the IC burned.
    What should i do? (replace all the transistors and diodes)
    thanks in advance
    Giniti

    ReplyDelete
    Replies
    1. Replace only the IC, rest of the things might be OK....

      Delete
  19. Hi Sir,

    Thank you for this project, I am really interested of making this one for my incubator. Just few queries if I may: (a) How can I set the low and high temperature levels? What pot/vr to tweak to?; (b) How can I set the hysteresis value?

    Thank you very much for your considerations.

    ReplyDelete
    Replies
    1. This circuit is without hysteresis.

      For adding a hysteresis control just add a 100K preset with a 10K series resistor across pin#2 and pin#6 of the IC.

      This preset may be suitably adjusted for getting the desired hysteresis.

      Delete
  20. Hello Swagatamk,

    I want to upload the scheme like you explain on 11, 2013 at 10:21 PM to prevent mistakes and later if this circuit works goed for me i will make the PCB and share it here.

    Giniti

    ReplyDelete
  21. i have a question for you and a proposition regarding this circuit . please email me at scholefield.chris@yahoo.co.uk for details

    ReplyDelete
  22. can these be supplied as a kit or a printed circuit board privided

    ReplyDelete
    Replies
    1. Yes it can be supplied as kits, If it's in large quantities....

      Delete
  23. Good day sir, im a noob when it comes to electronics, i just want to ask if what kind of resistor do i need to use as p1 so i can get a 37.778 degrees celcius temperature, i am planning to make a homemade incubator for my quails and i am assuming they will lay eggs in less than a week from now. i hope to get a reply soon from you sir, thank you in advance

    ReplyDelete
    Replies
    1. Hello, good day,

      P1 is a preset or a variable resistor, you will have to adjust it manually through some trial and error for obtaining the correct threshold cut-off , this will require a good prior knowledge of electronic basics.

      Delete
  24. Thank you for your quick reply sir, sorry for asking too much but i badly need your help regarding the thermostat. When you said that d5 must be placed away from ti, does that mean the only part that should be exposed inside the incubator to sense the heat would be T1? i hope to hear from you again sir. Thank you once again and i hope you continue helping noobs like us when it comes to electronics.

    ReplyDelete
    Replies
    1. yes, in other words only the diode should be kept out of the incubator in the normal atmospheric space...

      Delete
  25. thank you for your help sir. i really appreciate everything and i hope to read more articles regarding updates and improvements about the homemade thermostat and maybe incubator in the future. i was hoping to read an article from you about the auto egg roll and also i hope you can invent an electronic auto feeder for my quails. thanks in advance!

    ReplyDelete
    Replies
    1. Thanks, however my expertise lies in the electronic field, so a mechanical design would be difficult to think and produce....still I'll try to do it if possible...

      Delete
  26. HELLO SIR...IS THERE ANY OTHER FORM OF OPTO COPULER I CAN USE

    ReplyDelete
  27. GOOD DAY SIR...YOU ARE DOING A REAL AWESOME WORK HERE...I WILL LIKE TO KNOW IF THER IS ANY FORM OF INDICATOR TO SHOW IF THE CIRCUIT IS WORKING

    ReplyDelete
    Replies
    1. Thanks Hayzid

      you may add LEDs across pin6 and positive... and pin6 and negative, with individual series 1K resistors.

      Delete
  28. good day sir, i already build the circuit above and it is working well. my project, the relay it creates a buzzer like sound during turn on and turn off it is normal?i notice that it only create a buzzer like sound because of the led that is gradually glow. is there is any solution for this?

    ReplyDelete
    Replies
    1. Good day aian,

      connect a 33uF/25V capacitor across the base and positive of the transistor, this will stop the relay from buzzing.

      any other higher value capacitor will also do.

      Delete
  29. Well really its a informative post..
    I have a couple of questions. will yu please tell how to set the max and min temperature, which variable resister is to set max and which pot is tuned to set min temp..
    And why bc547 transister is near to heating device?
    Is it the thermal transister?

    ReplyDelete
    Replies
    1. Thanks!

      VR1 may be used for setting-up the cut off threshold, which must not exceed 110 degree Celsius (max), while P1 may be used for fine tuning the set cut off point.

      Delete
    2. The BC547 is used as the heat sensor here and therefore must be kept near the heat source.

      Delete
  30. Hi! Swagat, as this is more informative , can I know the heater size or rather the element size and if I think of afan tell me the size and the connection points. Thanks

    ReplyDelete
  31. hi, nice job. ive built 99% of the circuit. i just cnt make out the blue part adjacent to D6. please include details. Thanks

    ReplyDelete
    Replies
    1. The blue part is the relay coil......please click the diagram to enlarge and check the details.

      Delete
  32. Hay sir I have built it, its working good.
    8/10 Egg's hatched.

    But I gotta little trouble here, in the day time the temperature will be maintained as desired, but in the nights its on/off range will be lower by almost 5degrees.
    Ex: day= 37-39(perfect)
    Night= it goes 32-34(problem).
    All these days I use to tune for the desired temp twice a day.
    i guess its because of the room temp which will be lower in night at the ambient temperature diode.
    Suggest some replacement for this diode to make it constant all the time sir.

    ReplyDelete
    Replies
    1. That's great, if you look carefully you will find that actually the 1N4148 is not required, so you can simply remove it, and make VR1 into a 1K preset. Finished, now adjust the 1K preset for the desired actions.

      However in this case your power supply must be regulated, so add a 7812 IC after the bridge for making the supply stabilized.

      Delete
  33. Dear Swagtam
    I like the modified circuit version which I intend to build soon.Would appreciate if you could kindly explain how to add a LED to indicate when the system is on and off.

    ReplyDelete
    Replies
    1. connect one LED from pin6 to positive, another from pin6 to ground, both LEDs should have individual series 10k resistors.

      one of them will indicate ON, the other one as OFF.

      Delete
  34. hi sir in my place there is no an IC 741 and 4060 what are their altenertive

    ReplyDelete
  35. Replies
    1. if you don't get these, you won't get the other alternatives also for sure, consult the dealer, he will know better.

      Delete
  36. sir, is P1 a 10k? or 100k? and how do we tune the presets? is it VR1 or P1? and BC 547 is the only one who should be kept near the heat source? or is there any other components? thank you sir..

    ReplyDelete
    Replies
    1. for second diagram P1 = 1k,
      BC547 is the only sensor near heat source.
      keep P2 at center, set VR1 roughly to activate the relay at about 70 degree temp, after this only P2 may be used for getting other desired thresholds.

      Delete
    2. ....correction: for second diagram VR1 = 1k, P1 = 100k

      Delete
    3. Also sir where is the ground?

      Delete
  37. Is it normal that when you plug it in the bulb will kit? Our circuit it not turning off what could be the problem?

    ReplyDelete
    Replies
    1. Connect an LED in between R2 and collector of BC547.....keep pin2 of 741 disconnected with R2.
      Switch ON power and heat BC547 slightly at about 60 degree and adjust VR1 such that the LED starts glowing dimly...that's all your circuit is set.
      Now connect pin2 of 741 back in position, repeat the procedure and adjust P1 to activate relay at any desired temperature within 110 degree.

      Delete
    2. you can use soldering iron to heat the transistor...but be careful not to overheat BC547

      Delete
  38. thank you very much sir.. how can we get a computation for the thermal cut-offs?

    ReplyDelete
    Replies
    1. It basically depends on Ub (supply voltage), R1 and R2.
      R1 and R2 may be selected with the following formulas:

      R1 = (Ub - 0.6)/5 (kohms)
      R2 = (Ub - 1.5)/15 (kohns)

      these are the only computations available.

      Delete
  39. hey swag, i have a simple question. where should the ground connection of ic7812 and capacitor placed?

    ReplyDelete
  40. Please are the D5 and D6 diodes some heat censors?

    ReplyDelete
    Replies
    1. D5 and T1 are the sensors....T1 is the main sensor which needs to be kept near the heat source to be measured.

      Delete
  41. Hey sir..
    I was the one who said 8/10 egg's
    hatched, please read that
    comment again before answering
    this.
    i did 4 boards with the modified
    circuit with the following
    modifications
    1. gave LED in series with 10k.
    2.hyst 100k preset in series with
    10k resister.
    3. A capacitor across base and
    positive.
    Done everything as yu said.
    Still problem is'nt solved, all
    boards giving same problem.
    It works good and fine first day
    (completely accurate), but after a
    day the temp on/off range
    changes again.
    Sometimes it never turns OFF or
    ON, couldn't findout what is the
    prob.
    i think the room temperature
    again affecting its behaviour.

    ReplyDelete
    Replies
    1. Hi Rithesh,

      Remove the 100k hyst preset link, we do not need it at all because the heat will never rise or fall quickly, so a hysteresis feature is not required.

      Did you try the last circuit as given in the above article??

      Make it exactly as it's given...don't forget to use a 7812 IC with the circuit.

      Use good quality preset for both VR1 and P1.

      Make the above mods, it will work.

      With 1N4148 removed room temperature will not affect the circuit in anyway.

      In future you could think of replacing VR1, P1 with fixed resistors.

      Delete
  42. HIE SIR THANKS BUT MY QUESTION IS TO WHAT CAPACITY DOES THIS CIRCUIT HOLD IN TERMS OF NUMBER OF EGGS IN THE INCUBATOR AND HOW LONG DOES IT TAKE TO HATCH

    ReplyDelete
    Replies
    1. Hi Ngoni,

      It will depend on how many heat sources you are using, for each heat source you will have to incorporate an individual circuit.

      Hatching period is not known to me.

      Delete
  43. ok bro so for one individual circuit what is the capacity then how many eggs per circuit are we looking at

    ReplyDelete
    Replies
    1. It will depend on the area used, and the wattage of the heat source, it can be dimensioned to any desired range as per requirements.

      Delete
  44. thanks bro you are helping so much .is it proper to use one heat source for a 5m by 1.5m area and the heat source is an infrared light

    ReplyDelete
    Replies
    1. I have neve rused an IR light for heating purpose, how much heat does it produce?

      Delete
  45. l want to use any area of 5m by 1.5m so is one infrared light ok as a heat source

    ReplyDelete
  46. hie bro the infrared light a 250watt rating and what is the most desired heat source

    ReplyDelete
    Replies
    1. It will depend on the egg hatching specifications, you can get the information online regarding the right temperature required for hatching eggs. Then you can adjust the above circuit for maintaining the particular temperature range, throughout.

      Delete
  47. how many eggs would the box contain to do the process :D

    ReplyDelete
    Replies
    1. will depend on the size of the heat source.

      Delete
  48. hello sir swagatam, i already made the simplified version of your design, but it wont turn off the heat source ,,, if i adjust the vr1 manually, it will initialize turn on/off the relay but it wont turn off/on automatically to my desired temp, will you email me the step by step procedure in setting up my desired temp, cut-off,, tanx in advance

    ReplyDelete
    Replies
    1. hello Oliver, i am sorry it's not that easy.
      you can include an LED immediately after R2 and in series with it.
      Allow the transistor BC547 to heat up to around 70 degrees, and adjust VR1 to just make the LED glow.
      At this point you can try adjusting P1 for the required switching of the relay, or if it's already switched ON adjust P1 to just switch it OFF and then readjust to just switch it ON back.
      The circuit is set now and will repeat the actions every time the temp reaches the set threshold
      I hope you got it.

      Delete
  49. tanx a lot sir for the quick reply,,, maybe i can try the adjustment by next week coz i am out of town right now....i will follow the adjustment you say and update here the result ,,,

    ReplyDelete
  50. sir, i have a temperature controller built-in-type, in its user guide denote that use a snubber circuit for long life of relay of temperature controller, how can select the values of resistor and capacitor which involved in snubber circuit? i'm waiting for your suggestion....

    ReplyDelete
    Replies
    1. Khalid, that'll depend on many factors, you'll need to calculate it through an online snubber calculator software.

      Delete
  51. Good day Sir Swagatam, i will be making this projet and i will base on your circuit as a reference =) I only have samome basic concepts questions.

    What will happen to the Light (heater) if the heat goes up in the sensor? Will it dim or will it turn off?
    Which pots are assigned to set the temperatures from 0-120? Can it be made in a way that it that if (assuming) i set the min temperature to 20 degrees it will light up and shine brighter if lower temperatures are achieved? And 35 degrees it will dim?

    Or i got it all wrong? Hehehe sorry for asking a lot of question. I'm kinda new to these.

    ReplyDelete
    Replies
    1. Good day Lloyd, the heater will shut off for a moment if the heat exceeds above the set high threshold, and will switch ON back as the temperature falls below the lower threshold.

      The setting up adjustments could be done in the following manner:

      connect a RED LED in series with R2, and adjust VR1 until this LED begins glowing at the required high temperature from the heater (not to exceed 100 degrees C), ignore the relay response during this setting.

      the heater should not be connected through the relay rather directly through a manual switch

      Now once the above position is reached, carefully adjust P1 so that the relay just deactivates, if it's already in a deactivated position, force it to activate by adjusting P1 and immediately adjust it back to deactivate it, all these must be while the red LED is still glowing bright.

      your setting up procedure is complete now, connect the heater via the relay contacts as shown in the diagram, check and enjoy the automatic response as per the above settings.

      Delete
    2. ...for a dimming and brightening type of response you may refer to the following design:

      http://homemadecircuitsandschematics.blogspot.in/2013/01/automatic-temperatureclimate-controlled.html

      Delete
    3. Hi Sir, I don't know if my comment have been published. But just to be sure, i want to thank you again and i appreciate it very much for replying to my questions!
      I cannot find any way to private message you so i will put my request here to you..

      I changed my mind, instead i wanna make a 12v dc temperature controlled fan.

      I want it to make as such, it will turn on at 20 degrees and it will turn off below 20 degrees. If it reaches 20 degrees above, the speed of the fan will go faster aswell. The heat source will be the surrounding. And can we possibly add a LED, that will glow brighter aswell? I need as an example of a closed loop feedback control system. Please..

      Thank you again sir! I'll wait for your reply. Regards! (my gmail is here : rreddmallari@gmail.com)

      Delete
    4. Hi Lloyd, you can try the following circuit:

      http://1.bp.blogspot.com/-YmlmSYSqUTU/U7UWfVEzlHI/AAAAAAAAHcc/E6Uh_aI7rpA/s1600/solar+ater+heater+regulator+for+drip+irrigation.png

      Replace the heater with the fan, and the 9v supply with 12V

      Connect a red LED in series with the base of the transistor for the indications.

      Adjust P1 precisely so that the fan triggers at 20 degrees approximately.

      Delete

Readers are requested not to include external links while commenting. For consulting a diagram, upload it on Google Drive and provide the link here.

Readers are advised to proceed with the construction of the presented circuits only after understanding the concepts from the core. Not adhering to this can lead to failures and frustrations.