Photodiode and Infra LED: how to increase the sensitvity of photodiode,long distance

ikelectro · Sep 4, 2012

Im using a pair of photodiode and infra LED in a circuit. I placed the photo diode opposite of the Infra LED. The distance between them about 2 meter. if a person goes between this pair, then the photodiode will not recieve the light of infrared. and my circuit will give a buzzer tone. but the problem is that the distance 2 meter does not work. if i decrease it 1 meter and more less then it works perfectly. but I want to place them 2 meter away. what should i do now???

alec_t · Sep 4, 2012

Doubling the separation of the Tx and Rx reduces the received signal by a factor of 4, so you could compensate by using 4 IR LEDs.

ikelectro · Sep 4, 2012

alec_t said:
Doubling the separation of the Tx and Rx reduces the received signal by a factor of 4, so you could compensate by using 4 IR LEDs.

4 IR led and and 1photodiode. will be ok????

KJ6EAD · Sep 4, 2012

Add a simple dual convex lens to each element. Determine the focal length of the lens using a visible LED, then replace with the IRED or photodiode at the same position. Adjust the position of each element for greatest signal strength.

The lenses from an inexpensive hand loupe are a good option.

alec_t · Sep 4, 2012

will be ok?

Don't see why not. All 4 LEDs would need to be pulsed simultaneously (I assume you're using pulsed IR to overcome background light interference ?). Another option might be to use a collimator to concentrate (focus) all the IR from one LED into a very narrow beam. A third method would be to pulse the single LED at very high power but very briefly (to keep the average power well within spec).

ikelectro · Sep 4, 2012

KJ6EAD said:
Add a simple dual convex lens to each element. Determine the focal length of the lens using a visible LED, then replace with the IRED or photodiode at the same position. Adjust the position of each element for greatest signal strength.

The lenses from an inexpensive hand loupe are a good option.

ok i'll try your method also.

ikelectro · Sep 4, 2012

ikelectro said:
ok i'll try your method also.

im giving IRED around 10 KHz. is it ok?

audioguru · Sep 4, 2012

A photo-transistor is much more sensitive than a photo-diode.

alec_t · Sep 4, 2012

im giving IRED around 10 KHz. is it ok?

Should be, provided your Rx is tuned to that. You could, of course, use a more conventional 38kHz for which Rx ICs are readily available.

ikelectro · Sep 4, 2012

audioguru said:
A photo-transistor is much more sensitive than a photo-diode.

can you plz quote the No. of those photo transistor which is also in cheap and available in market.

alec_t · Sep 5, 2012

We have no idea what is 'cheap and available in market' in Kolkata. Try googling for photo transistors and local suppliers.

ikelectro · Sep 5, 2012

Ok, then can you just simply write down some good photo transistor's no?if you plz.

alec_t · Sep 5, 2012

There's hundreds of different types, e.g.
https://www.digikey.co.uk/product-s...ical-photo-detectors-phototransistors/1967049

audioguru · Sep 5, 2012

ikelectro said:
can you plz quote the No. of those photo transistor which is also in cheap and available in market.

Your "market" is on the other side of the world from me.
I look on the internet at the millions of modern parts at an electronics parts distributor like Digikey, order what I want then they are delivered to me the next morning.

MrAl · Sep 5, 2012

Hi,

To get good range using a regular IR LED and IR sensor you can modulate the IR LED at some fixed frequency and use a receiver with a front end filter to detect the light. It sounds like you are already modulating the IR LED, so all you need to do is build a filter. One of the problems is that the ambient light is usually also changing in intensity due to the nature of bulbs and other types of lighting. The light interferes with the IR light because there is some IR light from them too and also the detector might be sensitive to IR and other light too.
The filter can be a bandpass, but because most of the 'noise' light is at a very low frequency you can get away with a high pass filter. Say 5th order or something like that and you can even get away with a passive filter if you provide amplification after it. This can extend the usable range to several meters with standard components and drive power.

ikelectro · Sep 5, 2012

MrAl said:
Hi,

To get good range using a regular IR LED and IR sensor you can modulate the IR LED at some fixed frequency and use a receiver with a front end filter to detect the light. It sounds like you are already modulating the IR LED, so all you need to do is build a filter. One of the problems is that the ambient light is usually also changing in intensity due to the nature of bulbs and other types of lighting. The light interferes with the IR light because there is some IR light from them too and also the detector might be sensitive to IR and other light too.
The filter can be a bandpass, but because most of the 'noise' light is at a very low frequency you can get away with a high pass filter. Say 5th order or something like that and you can even get away with a passive filter if you provide amplification after it. This can extend the usable range to several meters with standard components and drive power.

HI,
Its a great info. but i dnt have any experience the word "filter" in this area. can you plz elaborate it and if you can give exapmle that'll be helpfull for me as Im new in electronics.!!

MrAl · Sep 5, 2012

Hi again,

A filter is an electronic circuit that removes some frequencies and leaves other frequencies more or less intact.

Here's a drawing of the simplest high pass filter. High pass means it passes mostly higher frequencies and rejects lower frequencies. The lower frequencies would come from other lighting in the room.

Code:

Vin  o---C---+---o Vout
             |
             R
             |
GND  o-------+---o GND

dougy83 · Sep 6, 2012

Here's a schematic for a laser pulse receiver I drew for a laser perimeter alarm. It expects very sharp pulse edges (fast rise-time), which should be perfect for your application. If you want to use this circuit, I'd suggest increasing the modulation frequency of the LED, as the circuit doesn't extend the pulse (although this is easy to do). Note that "I1" is the photodiode (phototransistor is too slow).

ikelectro · Sep 6, 2012

MrAl said:
Hi again,

A filter is an electronic circuit that removes some frequencies and leaves other frequencies more or less intact.

Here's a drawing of the simplest high pass filter. High pass means it passes mostly higher frequencies and rejects lower frequencies. The lower frequencies would come from other lighting in the room.

Code:

Vin o---C---+---o Vout | R | GND o-------+---o GND

thats very kind of you. but i want to asked what should be the value of the C and R in that case. any particular formula???

ikelectro · Sep 6, 2012

dougy83 said:
Here's a schematic for a laser pulse receiver I drew for a laser perimeter alarm. It expects very sharp pulse edges (fast rise-time), which should be perfect for your application. If you want to use this circuit, I'd suggest increasing the modulation frequency of the LED, as the circuit doesn't extend the pulse (although this is easy to do). Note that "I1" is the photodiode (phototransistor is too slow).

ok. this'll be very helpfull for me. but in that case how much distance I can cover with photodiode??

Photodiode and Infra LED: how to increase the sensitvity of photodiode,long distance

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