In this post I have explained a simple automatic PIR controlled ceiling fan circuit for school college use, which responds and switches ON only in the presence of a human (students) in the classroom. The idea was requested by Mr. Souren Bhattacharya.
Technical Specifications
I am, souren bhattacharya, a high school teacher in west bengal.
To reduce electricity used in my school classroom can you please make a circuit which can switch off/on fans (3/4 ceiling fans) in the classroom as per routine with a facility to manual override.
For example each class has one computer class and one physical education class in a week. we want to switch off ceiling fans when whole class is empty.
The Design
The design will require some kind of human IR sensor to be included, for example a PIR sensor device which looks to be the most efficient and effective for the proposed application.
Incorporating a PIR sensor makes the design pretty simple since most of the complex circuitry is handled within the unit itself.
The sensor just needs to be integrated with a triggering stage and a correctly rated power supply as shown in the following diagram.
Circuit Diagram
In the given diagram we are able to see a standard preprogrammed PIR module, a 7805 voltage regulator IC stage for supplying the PIR, and a simple 12 V transistor/relay driver stage.
The PIR Module
The PIR module has three terminals, the right one is the ground terminal, center one is the positive +3.3V or +5V, and the left terminal is the responsive output lead of the device.
When the particular assigned (+) and (-) terminals of the PIR device are connected to the specified supply voltages, the device instantly becomes responsive and begins "thinking".
No human presence or motion should be created in front of the unit's lens during this initial switch ON period for about a minute or so, until the device locks ON and puts itself into an alert or a ready stand by position.
The unit now becomes ready and responds to even the slightest human motion or presence in front of its lens by generating a positive supply at its output terminal.
This high at its output terminal persists as long as a human presence is detected within a radial range of around 20 meters in front of the PIR device.
Sensing Human Presence
The output turns into a zero voltage as soon as the human presence moves away or is removed.
The above well defined high/low voltage response at the output lead becomes ideally suited or accessible for a transistor relay driver stage as shown in the diagram.
When the PIR output is high due to the presence of a human (children in classroom), the transistor BC547 base receives the +3.3V out from the relevant lead of the device and quickly switches ON the relay.
The relay in turn switches ON the ceiling fan and the system stays ON as long as the students occupy the premise.
When the students leave and vacate the premise, the PIR instantly switches OFF its output to a zero voltage level.
However, the presence of the 470uF/25V capacitor at the output lead of the PIR prevents the BC547 from getting switched off instantly rather keeps it ON for a few seconds more after the PIR has reverted its output to zero.
After this delay the BC547 also gets deactivated, switching OFF the relay and the ceiling fan or any other desired load whatsoever that may be wired with the relay.
The above circuit may be effectively modified as given below for operating lights, with a feature making sure that it's implemented only during the night time and not during the daytime when ample daylight is accessible. The idea was requested by Mr. Sham.
Questions & Answers
if any animal comes it will get on? i mean cat or dog? if human motion is not there will it remain on position?
yes it'll detect all warm blooded living beings..
with nobody in the range the unit will stay shut off…and get activated when the same is detected
how many circuits are required for controlling 3/4 fans in a 350 sq/ft class room.?? is the sensor is available in kolkata?/
A single unit would take care of each room comfortably, preferably it could be positioned on the center of the ceiling in order to get a radial view of the classroom.
All the fans could be controlled through the single relay for getting a simultaneous ON/OFF toggling.
PIR sensors have become too common nowadays, so it should be easily available in Kolkata too.
When I needs to change the speed of the fan then what happens otherwise it's controlled by human manually?
speed control has no connection with the above circuit, it'll need to be controlled through a series regulator as usual
If I used the sensor for a cfl light or tube light, when I entire the dark room then it worked properly?
yes it will work.
Sir from where I will get PIR sensor and is it costly
yes it will be a bit costly, inquire with your local electronic retailer, he'll know better.
Sir, the problem I am facing after making the sensor is that .. If I have set the delay timing for 30sec.. And i am sitting in that area ideally i.e. there is no physical movement it would get automatically turn off after the delay timing.. Can u plzz suggest me how to rectify this problem of mine..
Ankur, PIR devices are designed for sensing IR from our bodies not for sensing motion….so if it's not sensing your presence then may be you are not in the range of the device or there's some fault in the system components.
What will happen if I use 7812 for output of 12v when input of 12vDC instead of 7805 as +5v regulator ?
PIR device will burn ?
Please clear my concept.
if your PIR is specified to work with 5V then surely it will burn.
sir what should i use as a 12v dc supply… should i design a rectifier circuit separately?…. or using a 12v battery could be a better option?… please guide..
Thanks
Ashish, the 12V could be from a ready made 12V AC/DC adapter unit or any similar power supply.
sir can know the connections of relay 12v spdt in the diagram clearly , that i was new to electronics
manjunath please go through the following article for more info:
https://www.homemade-circuits.com/2012/01/how-to-understand-and-use-relay-in.html
sir I had gone through above link but I have some doubts please solve it sure I will success in this circuit
1) which diod( number of diod) has connected from pir output
2) wheather both side of relay coil are same ( output and input) mean which side of coil is connected to collecter bc 547 and which side of coil to 7805
ground.
3) As in diagram first wire of 220v is connected to realy n/c and that 220v wire ic connected to fan and where to connect other wire of fan to
manjunath,
the diode can be a 1N4007
relay coil does not have a polarity, so you can simply connect it anyway round across the shown points.
an AC load will never have a polarity, so here too the shown load (fan) may be connected anyway round across the indicated locations
sir i had build the circuit as shown in diagram and connected light instead of fan and it seems to be not working properly, means if i close the sensor with paper or if nobody present in an range of sensor also the light glows, and while glowing if i went near the light will switches off for few seconds and then glows agalin by making small tik sound . what it means and i was not sure about connecting wire to relay.
i had connected 220 v one wire to nc and and another wire to light and then another wire of light to relays " com" NO of relay has been left without any connection
where the mistake has been occured please suggest me sir,
sorry for my bad english
sure
Manjunath, you can first confirm the working of the PIR sensor separately by connecting an LED across its out and ground pins, while doing this you can keep the relay disconnected from the transistor.
check how the LED responds in the presence or absence of a human body, this will confirm whether the fault is in the PIR or the transistor driver stage.
sir, i had tested pir sensor with both buzzer and led. it was working properly,
then what may be the problem, please help me to correct the circuit . thanks
please check it in the present set up that you have made, or alternatively you can connect an LED in series with the transistor base resistor, if this LED toggles as per the specs, but the relay doesn't then the fault could be in the transistor….for more info you can connect another LED parallel with the relay coil with a series 1k resistor…
check response from all these LEDs, it will help you to pin point the issue.
sir i had made new circuit of the same above, because of that i cant find the faulty stage. as i am an new to electronics but this was also the same as above so i dicided to send the real picture of my circuit made if you agree. i was so intersted that i dont want to leave this thanks
manjunath, please do the steps which I mentioned in the previous comment, this is only way you'd be able to troubleshoot the circuit.
pls do it and check the results
sir please can you discribe the method of connecting an LED in series with the transistor base resistor to check th faulty stage, or any site address reguarding this . thank you for your cooperation.
Manjunath, cut the link between the transistor base and the 1k resistor and then connect the longer lead of the LED with the 1K and the shorter lead with the base of the transistor
SIR, i had made above test by connecting led to transistor base, and another led to relay coil with 1k resistor . both led responce to sensor but led connected to transisitor was too low bright.(was any mistake in this stage) when i switch on both circuit and relay load , even though if no body present in front of sensor it goes on running,and if i move in front of sensor it switch off the load for few seconds and then goes on glowing. please slove this
thanking you
The transistor base LED and the relay LED should light up together in the presence of a human in the zone and shut off permanently in the absence of a a human being
If the LEDs are lighting up with nobody around then there could be something wrong with your PIR device.
sir, sorry to disturb you that i had connected new pir sensor but it was working as before it had. in this comment section interested peoples who suceeded in this project please help me as i am not to disturb this comment section.
was this an right swagatham sir , my mail id
manjujain06@gmail.com
The transistor base LED and the relay LED should light up together in the presence of a human in the zone and shut off permanently in the absence of a a human being
If the LEDs are lighting up with nobody around then there could be something wrong with your PIR device.
Please let me know the model of the PIR sensor that you've used, so that I could help you further in this regard.
sir i had used and tested " robodo hc-sr501" in this one is having trigger i think.
thank you
As far as I know, HC-SR501 sensor has its Vcc on the left and its control signal pin is its centre pin. If you have connected it correctly, it is not an issue but if you didn't, then you have to interchange the connections between Vcc and signal pin ACCORDING TO CIRCUIT DIAGRAM ABOVE.
If still it does not work, try replacing the transistor as you told that you even tried using a new pir sensor in one of your above comments.
Also recheck the connections that you've made and correct them (if any).
Above steps might solve your problem. Even after following above steps, if your cicuit does not work, try troubleshooting the circuit according to the instructions given by our senior, Swagatam sir.
sir, this project also succeded with your guidence. thanks a lot.
but as shown in diagram and reffering to relay topic, i had confused that wheather relay load has to connect to "NC or NO"
but my circuit working .SIR this just to clarify, thanks
Thanks Manjunath, in the article the PIR is assumed to generate a high pulse on detection of a subject, so the shown connections of the load to the relay is correct, it's across the N/O point….N/C is open
Hi Swagatam,
I have tried the above circuit for my kitchen light. It is working perfectly and a great way conserve energy. My kitchen has sufficient daylight during day time so i dont need pir to switch on the light during day time. I need it only during absence of daylight. How to get this done by using LDR in the above circuit?
I have seen your other articles on PIR but it seems to be complicate for me with dual relays and 555 timer. Please show me a simple way to do this.
Thanks,
Sham.
Hi Sham, glad to know that the circuit is serving the purpose for you.
I'll upgrade the diagram as per your requirement, and post it soon in the above….please keep in touch.
Thanks Swagatam. Looking forward to it.
Hi Sham, it's been updated, you can check it out
Ho very nice. Sure will check tomorrow and inform u. Thanks a lot Swagatam.
you are welcome sham…
Hi Swagatam,
I could not get back early. Please excuse me.
Tested the circuit today. Its working perfectly well. Once again hats off to you and thank you so much.
Hi Sham, that's great, congrats to you on that. I am glad the circuit worked as intended.
Swagatam,
I noticed that at some point of light intensity, the relay toggles continuously. I have placed the LDR on the other side of the light source. As the daylight fades off the relay started to toggle. Looks like it is not getting latched. How to fix this defect?
I have used 4.7uf across CE of LDR ckt and 100uf from BE of PIR ckt. Since i did not have 1uf and 470uf cap.
Hi Sham, the light from the PIR lamp should not be allowed to fall on the LDR, otherwise it'll malfunction.
also for a stable response you can try connecting a 10uF/25V capacitor directly across the relay coil
And btw i am using 100k pot at the base of LDR 547.
OK. I got some suggestion from your other article.
https://www.homemade-circuits.com/2011/12/super-simple-light-activated-switch.html
I will try this and update you.
Sham.