IR (Infrared) Security Alarm System




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In this project, you will build transmitter and receiver circuits using an IR LED and a photo-diode. The circuit is based on obstacle detection when a person or thing comes in between the transmitter and receiver. The alarm gets triggered and beeps continuously till the time the circuit is reset.

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46 Discussions

daisy joyt

Question 1 year ago

Hi! I've made sure I've followed all the instructions but the buzzer started buzzing the moment I connected the battery. What should I do??? Please help


Question 1 year ago

I have purchased one of your DIY KITS. I have made sure all connections are perfect but yet, the buzzer in the transmitter circuit starts buzzing just as I connect the battery to the transmitter circuit.
could you suggest me what could be done to rectify this error for the proper working of the circuit.
Hoping for a quick reply.

3 answers

Answer 1 year ago

Thanks, mandlabs for your prompt reply.
I will get back to you once I apply your suggestions to my project.
If it doesn't work I will send the pictures of my circuit to you soon.
Hope to stay in constant touch with your team since I have to get my circuit working within the coming Sunday evening.
As I have to submit my project on Monday.
Thanks Again

mandlabs lalithk_2000

Answer 1 year ago


We were waiting for your reply. We have not got the opportunity to review your circuit. We anticipate a few potential mistakes. We are giving you a few pointers. #See pointer 5. You will need to check them all one by one:

1. The stripped portions of wires that go inside the breadboard must be at least 1 cm in length. Check all the wires and their lengths and ensure that the tip of the stripped end touches the inside metal strip.

2. The positive terminal of the photo-diode in the receiver circuit must be connected to ground.

3. Check whether the negative terminal of the buzzer and the green wire going to the NO terminal of the relay are connected in the same column.

4. Ensure that the relay is tightly fitted onto the breadboard. Take your battery. Connect its two terminals to the supply terminals of the relay (the two opposite terminals). See the top side of the relay. There are three legs. The middle terminal is the common terminal (COM) and side terminals are the supply terminals. You should hear a click sound. Please note the battery voltage should be more than 9V in any case. Check the voltage using your multimeter (tutorial included in the video)

5. In case your buzzer starts beeping. Here is what you need to do next:
5.1 Bring both the circuits completely closer to each other. Ensure that both the LEDs face each other. Try to adjust the line of sight LEDs so that the buzzer gets Off. This is a trial and error method.

5.2 Then slowly introduce any obstacle to check whether your circuit works fine. Since the distance b/w the LEDs will be quite less, you can even introduce a black paper/scale/ etc.

5.2 Once you reach there, keep the transmitter circuit fixed and slowly move the receiver circuit keeping the line of sight intact. There comes a point when buzzer will start producing a meagre beep sound. That is the point at where you need to stop.

5. Ensure that the transistor used is an NPN transistor (547B). This number is imprinted on the flat surface of the transistor.

Please follow these recommendations. One more thing- don't give up too soon! One last thing, if your circuit still does not work, we will be happy to send you a free pair of powerful IR LED and photodiode.

mandlabs lalithk_2000

Answer 1 year ago


Thanks for reaching out to us. Lets solve your problem. Could you please send us high quality pictures of your assembled circuit from top and side angles at This is the best way to get technical support. Our engineers will review your circuit and give suggestions. We are eagerly waiting for your reply. Regards, support team, Mand Labs


2 years ago

Can anyone tell me which type of relay used here.

2 replies
mandlabs pankajp

Reply 2 years ago

Hi pankajp, this is an SPDT relay -12 V


Reply 1 year ago

Dear Ajith,

You can modify the project to your needs. If you can replace the normal IR LED and photo-diode with more powerful IR LED and receiver, you will have a no-zone line of sight that can be installed in places where no movement is a requirement.

Thank you so much ! Yes, the circuit instructions were built with the intention that beginners could build it. We are a kit manufacturers/maker company. We are glad to get your response.

mandlabs syamla

Reply 1 year ago

We are not sure why you said "batteries not connected to a circuit"? W/o the batteries, the circuit won't work. We use a 9V supply to power both the transmitter and receiver circuits.

mandlabs visuu1

Reply 1 year ago

You can use either an NPN or a PNP. Using NPNs are more convenient for switching purpose. Hope this helps.

mandlabs DanielL291

Reply 2 years ago

Hi DanieL291,

thanks for the comment. We are not sure from where you could get a photodiode? you might wanna check out adafruit or spark fun in US. Happy to answer any more queries, if you have any. BTW, we are soon coming up with our Indiegogo campaign:

let us keep talking,