Introduction: 9V IR Detector

Picture of 9V IR Detector

This is a great, simple project to make a small and robust 9V IR detector. It can be used to seek out security cameras that use infrared light to "see" or to check if your remote control is still working.

Step 1: What You Need

Picture of What You Need

For this project you will need:
-A 9V battery clip with a flat cover made of plastic
-A 9V battery
-LED (any color although it should be clear in order to see it better)
-330 ohm resistor (orange-orange-brown-gold or silver)
-Infrared Phototransistor
-perf board (see 2nd picture)
-double sided mounting tape
-needlenose pliers
-wire snipper
-dremel or hack saw to cut perf board
-clear epoxy-like glue
-Soldering equipement:
      -soldering iron
      -solder with flux core

A shematic is given in step 12, picture #4.

Step 2: Assembly Part 1

Picture of Assembly Part 1

First up is putting the LED in. Bend the leads over and insert it in the perf board like in the picture (note that you should start in the corner to make our application as small as possible)

Step 3: Assembly Part 2

Picture of Assembly Part 2

Next, put in the 330 ohm resistor like in the two pictures.

Step 4: Assembly Part 3

Picture of Assembly Part 3

The last step is to insert the IR Phototransistor like in the pictures. Pay attention that with this part the long lead faces the negative pole.

Step 5: Soldering

Picture of Soldering

After step 2-4 you'll need to solder the parts to the perf board to make your detector usable.
If you're a first-time solderer, you should watch this video: .
(I didn't make the video, thanks go to CuriousInventor)
After soldering, your project should look like the example in the first picture.
Then, clip off the excess component leads, making sure not to break the solder joints.

Step 6: A Bit More Soldering

Picture of A Bit More Soldering

To finish off the soldering part, you'll need to connect two soldering pads like in picture 1.
For the bridge you can take a snipped off lead from one of the components. I first bent my lead to put it through
the holefor stabilisation like in picture 2, but you don't have to. The result is all that counts.

Step 7: Cutting

Picture of Cutting

After soldering, you'll need to saw/cut off the excess perf board.
Make sure you leave space for the negative & positive wires that are connected to the battery.

Step 8: Attaching the 9V Battery Clip

Picture of Attaching the 9V Battery Clip

Take your hardcover 9V battery clip and cut it's wires to about 1/2 inch (1,4mm) lenth like in the 2nd picture.
Then solder the battery clip to your detector and make sure you get the polarity right!
After soldering your gagdet should look like pictures 3 & 4.
To prepare it for the next step, twist the 9V battery clip so it can be bent under the circuit like in picture nr.1.

Now is a good time to check if your device works. Carefully clip it on a 9V battery.
If you try it out during the day, the LED will be partially on depending on how bright it is where you are.
To be sure that it works point the Phototransistor to the sun/roomlight and put your finger over it.
The LED should get dimmer when your finger is in the way. If nothing works, check out the last step for possible solutions.

Step 9: Using the Mounting Tape

Picture of Using the Mounting Tape

Next up is fastening the circuit to the battery clip, the most efficient way I found is to use double sided mounting tape.
To keep everything in place for the tape to stick and for the next step I used wire to wrap it up.

Step 10: Glue Is the Solution

Picture of Glue Is the Solution

To ensure the detector's long life, glue is used. Just cover up the circuit (except for the LED and the IR Phototransistor), the border on both sides of the mounting tape and the wires from the battery clip with a thin coating of epoxy glue. Let the glue dry over night.

Step 11: Last Step!

Picture of Last Step!

After letting the glue dry take off the wire used to let the mounting tape & glue bond.
If you have problems taking off the wire then you've put too much glue on, but that won't affect the
functionality of your device.

Step 12: You're Done!/Problemfixes&circuit Diagram

Picture of You're Done!/Problemfixes&circuit Diagram

If you jumped to this step because you have problems with your devices:
1. Check if your battery has enough juice (the "putting the contacts on the tongue" trick will work)
2. Make sure all the solderconnections are nice & smooth
3. Check if there any shorts in the circuit (solderbridges that shouldn't be there)
4. Check if any leads/wires from the parts or battery connector are broken, sometimes too much stress
    on the parts makes them break.
5. Did you put the LED & Phototransistor in the right way around / did you get the polarity right?
As a help I added a circuit diagram as pic #4.

For all the others:
Fetch a 9V battery and try your IR detector. Clip it on and... you're done! Have fun!

Comment, rate & follow!


Monoclecat (author)2011-05-02

I now added a circuit diagram, as seen on step 12, picture #4.
I hope it answeres most of your questions, if not, let me know.

ShyG (author)2015-07-23

i read this in electronics for dummies but cool tho

mohammadqa (author)2015-05-18

John PaulS (author)2014-12-01

if im going to make an ir transmitter for this receiver can i just connect a 9v battery to an ir led near the ir receiver?

Monoclecat (author)John PaulS2014-12-01

Yes, but add a resistor in series with the LED. 470 ohms should do it.

Rocker517 (author)2014-06-25

Is it possible to use a photodiode instead of a phototransistor on this project?

Monoclecat (author)Rocker5172014-06-26

No, this won't be possible. A photodiode is not a "switch" that closes when light hits it. Think of a photodiode as more of a solar cell that creates a current when light hits it. You will need a phototransistor that will switch currents when light hits it.


yo ksh_sha (author)2014-02-23

what type of IR transistor are you using,

can you tell it's serial no. ?

can we get it from any home appliance ?

Monoclecat (author)yo ksh_sha2014-02-23

This project is a while back, I cannot find the source I got it from.

Any IR transistor that isn't frequency-specific will work.

You can get IR transistors from TVs.

da_noah (author)2014-01-16

great instructable but one question. the arrow with a line at the end, where it is circled and 2 arrows are pointed outward. what is that represented in this specific instructable? i'm kinda new to this

Monoclecat (author)da_noah2014-01-17

That's the schematic symbol for a LED (Light emitting diode). It's the circuit component that lights up when in use.

This schematic symbol without the circle and the arrows pointing outward would be the symbol for a standard diode.

If you need more information check out this wikipedia page:

Jacky P (author)2013-11-23

What does the resistor do? I'm kinda new to electronics.

Monoclecat (author)Jacky P2013-11-23

Because we are powering the LED with a 9V battery, which would blow the LED as a result of too much current flowing through it, we need a resistor (could be 330 to 1k ohm, depending on the color of the LED) to regulate the current so that it doesn't blow the LED.

bertwert (author)2013-08-10

You could easily make this into a receiving end of a laser tag system by changing the led into an alarm and add a switch that can stay on.
To make the sending end, connect a IR led to a battery, resistor and micro switch.

m1s73r (author)2011-11-15

Is it possible to increase the range of the IR Phototransistor? I've tried it with my TV remote but it does only work in range of approximately 4 inches... Also, I have an idea, couldn't you add a red LED, which light up if no Infrared Signal is in near?


electro18 (author)m1s73r2012-11-13

I added some NPN transistors and whoa! i made a perfect IR proximity sensor !

Monoclecat (author)m1s73r2011-11-26

It's not that easy to increase the range of the phototransistor because if you would, you would also get more false readings because the natural light would be recognized more. The actual reason why the remote must be in a range of 4 inches is because th IR LED of the remote is too weak. The TV can sense the IR LED because the remote lets it flash at a certain frequency, which makes it possible for the TV to concentrate on the remote's light and cancel out other IR light sources, linke natural light.
You could add a red LED, but that would use up too much circuit board space to make it fit on a 9V battery clip.

mraghib (author)2012-05-30

How do I differentiate between infrared phototransistor and infrarered led?

Thank You

Monoclecat (author)mraghib2012-06-02

I think your problem could be that you accidentally used an infrared LED instead of an IR transistor.
IR transistors and IR LEDs are very hard to differentiate by how they look like,
but the way you described your problem lets me think you used an IR LED.
To be sure, plug in your 9V battery and take a digital camera (or the camera in your cellphone) and point it at the IR LED. If you see a light coming from the LED on the display of your camera (note that you cannot see this light!) you know that you've used an infrared LED and not an infrared trasistor like you should.

I hope I could help you fix your problem, if now I'll be glad to help some more!

mraghib (author)2012-05-30

Dear Sir,

I think my detector is not working. When i connect it with the 9 volt battery the LED turns on from first only and when I bring it near to my tv remote and press the tv buttons nothing special happens! I have checked and rechecked the steps.

By the way in step number 13 you did not mention how or when will 'it' turn on, you have just written it should turn on. Please help!

Thank You

axeman911 (author)2011-10-07

is an Infrared Phototransistor the same thing as a infrared LED?

Monoclecat (author)axeman9112011-10-09

No, an infrared LED emitts light, but an infrared phototransistor senses light.

axeman911 (author)Monoclecat2011-10-09

so what would happen if i were to replace it with an infrared LED would that detect anything or would it like interrupt signals or anything?

Monoclecat (author)axeman9112011-10-09

No, that would only make the project act like a infrared flashlight and won't have any detecting abilities at all.

kill-a-watt (author)2011-06-05

Don't you need a filter that passes (near)-IR only as a filter, or is the detector itself sufficient to avoid triggers from visible light?

Monoclecat (author)kill-a-watt2011-06-20

You shouldn't need a filter because if you use an Infrared phototransistor, it will only trigger when pointed to IR light.
The detector though will register some IR light when used in sunlight, as it containes light from the infrared spectrum.

aesquivel (author)2011-05-02

Will the battery drain if no IR is detected?

Monoclecat (author)aesquivel2011-05-03

No because if no light is detected, the IR Phototransisitor won't let any electricity flow.

kill-a-watt (author)Monoclecat2011-06-05

I'd measure that to be sure. If it's only a few milliamperes then you won't notice any difference compared to the shelf life of the battery, so it would not matter. Otherwise, adding a switch or removing it from the battery should do the trick.

Monoclecat (author)kill-a-watt2011-06-20

Yes, a switch would be a possibility.
On the other hand, you could just remove the detector from the battery to be sure that no eletricity is wasted.

arbita2 (author)2011-06-04

good good good

kel noseh (author)2011-05-29

simpleness is greatness

skrubol (author)2011-05-10

You have the LED labeled as Infrared LED. That should be visible LED shouldn't it?

If you need higher sensitivity, there are also photodarlingtons, which, if you aren't familiar with darlington transistor configurations, have 10-100x the gain.

Monoclecat (author)skrubol2011-05-11

Oh thanks, I'll fix that right away.

falcotheimpaler (author)2011-05-09

Now, if this does what i'm assuming it does, the LED should pulse with the frequency of the IR code being sent to the transistor.
if so, one could replace the LED with another IR LED, (and potentially an extension lead) and create a low-cost IR repeater, for using remotes across corners, in other rooms, etc.
(I tend to find practical uses for things like this)

XOIIO (author)2011-05-09

Not a bad idea, I used to build these to test if remotes were working. As for detecting night vision cameras, they do horribly. Not enough LED's to pick them up well, and these IR LEDS are weak, they only work well within 10 feet, otherwise they barely do anything.

robot1398 (author)2011-04-28

the same instructable

pdub77 (author)robot13982011-05-01

I would argue that this is not the same. This build is quite a bit more elegant and therefore worthy of its own instructable.

robot1398 (author)pdub772011-05-08

u r correct

AT (author)2011-05-03

I just love simple! Great project.

I know why you used a 330 ohm resistor. Not everyone will. Could you add a simple calculation on why a 330 ohm resistor with the 9v battery? :-)

Monoclecat (author)AT2011-05-04

Well I haven't done many calculations lately, but I'll have a try:

I * R = E

0,012amps * 330ohm = 3.96volts

which is safe enough for the clear LEDs

AT (author)Monoclecat2011-05-05

Just a simple Ohm's Law should do it. :-)

Goodhart (author)2011-05-04

The schematic has the output LED labeled Infrared LED which means one could not see if it were ON or not (and once it was on, it would keep the IR phototransistor ON and drain the battery.

der_fisherman (author)2011-05-01


great idea and could be very useful when testing for IR from remotes and the like, but I personally always like to see a circuit diagram before building anything, even something this simple/easy......can you add a simple sketch of the connections.

I could probably work it out myself, but me being born lazy......

For anyone else who maybe wants to understand the operation better, they may agree with me.

Full marks though for simplicity and ease of use, many thanks.

PS If there is already one here and I did not see it, I am VERY unobservant, apologies/sorry!

Venemot (author)der_fisherman2011-05-03

Well actually there is.....the last pic on the last page is a schematic of the whole circuit...!!!!

der_fisherman (author)Venemot2011-05-04

Many thanks, I thought I may have overlooked it somehow.....

kill-a-watt (author)Venemot2011-05-03

I might suggest that at least add text to the intro saying there's a schematic on step 12. You may think it's so simple that the schematic is not needed, and that's true, but think of the diagram as a "Cliff's notes" of the project.

First thing I did was hit "show all steps" and then skim for the schematic (and then fav your project).

techrobo (author)2011-05-02


MadCobbler (author)2011-05-02

I love minimal component projects, but a schematic or circuit diagram would help clarify what your are doing.

azharjaved2000 (author)2011-05-02


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