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How to Connect an IR Photodiode Sensor

In this post we learn how to correctly connect an IR photodiode in circuits such as a proximity sensor circuit. The explanation is presented in the form a discussion between one of the dedicated readers of this blog NVD, and me.

Here's the discussion which explains how to connect a photodiode in an electronic circuit

can you please tell me whether following circuit work or not. i think output of ic is 5v.i I want the output to be connected to a 12v relay instead of buzzer..can you tell what alterations should i make in the circuit..

IR proximity detector circuit
photodiode IR image with polarity anode cathode
(+) is the Anode, and (-) is the Cathode

  • NvD, if it's set correctly then it should work..
  • you can use a BC547/relay stage at the output of the opamp, the base resistor cold be 10K
thank you sir
can u give me circuit of bc547 relay driver circuit

  • NvD, you can refer to the following article
ok sir
sir is there any positive and negative terminal for ir reciever and transmitter like led.Im new to to this,thats why asking

  • NvD, just like any other diode, IR photo-diodes also have polarity and must be connected accordingly.
in the circuit, photodiode is connected forward it wrong? Please check sir

  • NVD, the transmitter IR photodiode polarity is correct...receiver polarity is wrong, needs to be inverted for the receiver as shown below.

sir,firstly i forgot to connect ic pin 3 to transmiter resistor then i have given a supply of 12v.led lits only.after that i connected pin 3 to resistor and given 9v.Now led lits when i turn the variable resister to one side.led doesnt lit when obstacle is brought in front.pls help me sir

  • did you invert the LED polarity which is connected with the pin#3?? first do this. then adjust the preset until the output LED just shuts off.
  • after this you can switch ON the transmitter photoLED, keep it parallel to the pin3 photoLED and bring an obstacle in front of the two sensors and check the response
  • cathode of the pin#3 photo LED must connect with the positive line....This is how any IR photodiode needs to be connected in a given electronic circuit

sir, i connected everything properly.still it doesnt work.i there any chance of ic or photodiode burn off when i connected 12v you have any circuit diagram for ir proximity senser

  • NVD, the photodiode will never burn as long as its connected in series with a resistor.
  • bring the transmitter close to the Rx diode manually and check whether it responds or not, also while doing this check the voltage at pin3...remember pin3 preset should be set in such a way that without the Tx signal its potential should be just below the pin2 must fix this first.    

Feedback from Mr. Norman Kelley (one of the avid readers of this blog):

Hi, Swagatam,

I have been looking for a circuit to alert me when someone enters my courtyard and front deck. 

Delivery people leave things on the front deck and do not ring the door bell, so I don't know my packages are on the deck. Also, at night, I would like to know if someone enters my courtyard. 

I designed a circuit with a PIR and a wireless TX/RX to play a message inside my house. Everything works but there are many false triggers and it drives my wife nuts. 

I am assuming that the RF signals are triggering the PIR. I tried separating them a few inches and it helped, but not enough. So, I decided to look at IR to detect the person opening the gate to the courtyard and then wirelessly transmitting that trigger. I wanted to do an IR beam, but it requires more components that I don't have at this time. 

So, I decided a proximity IR would work if I placed the sensor at the gate and put a reflector on the gate that would reflect the IR when the gate was opened. 

I saw your above circuit "How to connect an IR Photodiode Sensor". 

I bread boarded the circuit and it works fine. The only problem is it uses 50ma in standby mode and 70ma when active. 

Remote mounting with battery power supply seems to be out of the question unless there is a way to reduce the power requirements or I will have to run low voltage out to the unit. 

Any suggestions or comments? Thanks for your help!

Norman Kelley

My Response:

Hi Norman,

The high consumption could be simply due to the incorrect LED resistor values, try using 1K for transmitter LED and also for the indicator LED, the total consumption should come down to around 6mA

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    1. sir
      is it possible to connect 5v relay instead of any alteration to be made for this

      1. yes, you can replace the buzzer with a relay driver stage as explained below

      2. wat will be value of base resister

    2. sir
      can you please tell me whether this circuit works or not

      1. Raj, It might work if the BC557 is a Darlington transistor, and also it is incorrectly presented as an NPN...correction is required.


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