photodiode receiver range problem

[EmmKay]

Hi All,
I have the following circuit which is detecting a 1mw 650nm laser pulse of 10Hz from a distance of 250 meters. The receiver has a red filter to reduce ambient light noise. The receiver and the laser are placed on a boundry wall outside in direct sunlight. The problem that I am having is first related to temp. currently the outside temp is 52 degrees C. afer 45 degrees the receiver has problems with latching on to the laser pulse. I changed the inductor from 1mh to 2.2mH 3 Watts and that seemed to work for temps upto 45 degrees. but at temps above that I still have problems. Also with the larger inductor I seem to have noise and range issues. i.e. the range goes down to less than 200 meters.

As I would like to extend the range to approx 700 meters. I will upgrade the transmitter to a 5mw 635nm laser so that should work in theory atleast. I need help in making certain that the receiver can cope with that

Any and all help is appreciated.

 

[ericgibbs]

Hi All,
I have the following circuit which is detecting a 1mw 650nm laser pulse of 10Hz from a distance of 250 meters. The receiver has a red filter to reduce ambient light noise. The receiver and the laser are placed on a boundry wall outside in direct sunlight. The problem that I am having is first related to temp. currently the outside temp is 52 degrees C. afer 45 degrees the receiver has problems with latching on to the laser pulse. I changed the inductor from 1mh to 2.2mH 3 Watts and that seemed to work for temps upto 45 degrees. but at temps above that I still have problems. Also with the larger inductor I seem to have noise and range issues. i.e. the range goes down to less than 200 meters.

As I would like to extend the range to approx 700 meters. I will upgrade the transmitter to a 5mw 635nm laser so that should work in theory atleast. I need help in making certain that the receiver can cope with that

Any and all help is appreciated.

hi,
If I am reading your circuit correctly you appear to have no temperature compensation on that transistor, the Vbe will change by approx 2mV/Cdeg change.
IMHO the circuit is too 'basic' to give the results you want, over that distance and ambient tempr range.

EDIT:
Is that the full circuit.???

 

[EmmKay]

@eric.. thank you for the interest.!

The output signal goes into an lm311.. which compares the signal with a ref voltage and outputs accordingly.. thats the complete circuit!!!!!
the output of the lm311 goes into an atmel.

I upgraded the transmitter to a 5mw 650nm laser, kept the receiver as it is.. did some testing in morning in 47 degrees C. The maximum range I could manage was 361 meters before the receiver started responding intermittently. At 472 meters I couldn't pick up the signal at all.

Temperature issue only happens for a couple of weeks in a year when we get upto 55 degrees C. and for a couple of months it is between 40 and 46 degrees C (Can live with that for the moment!). Main thing being increasing the range and reducing the ambient noise.

 

[audioguru]

You show the IR detector diode connected backwards so it is conducting all the time.

An IR detector diode can be used two ways:
1) It is reverse-biased so with no light it does not conduct. Light makes the reverse-biased junction "leak" a small current.
2) It has no bias voltage and performs like a tiny solar cell and produces a small current and a small voltage.

You show a PNP transistor with no collector voltage and no collector current. If its base and collector resistors connect to ground instead of to nothing then the poorly biased transistor will be saturated all the time and still won't work.

 

[EmmKay]

@audioguru,
Its good to see your contribution, you have helped me a lot in the past with the fm transmitter for which I am very greatful.

you mentioned that the pnp transistor has no collector voltage and hence no collector current. the circuit is a legacy from an old employee of the company, I built it and tested it and it works.. hence my confusion as to your statement of 'still won't work'

The built circuit has been running since last year june when i interfaced it to your suggested modified FM transmitter circuit.

The only thing that has cropped up since is the requirement for extended range and dealing with high temps. As in the earlier post of mine, I did get the range upto 361 meters without any problems and upto 471 meters with intermittent signal loss! by changing the transmitter laser to a higher wattage!!! perhaps there is something that you might have missed in the schematic!!!!!!

 

[audioguru]

Your photo-diode will not work since it is shown backwards. Maybe you have its pins connected correctly.
Your 68 ohms value for R1 is almost a dead short, it should be much higher.
Why do you have an inductor?

I reverse-biased the photo-diode, increased the value of R1, removed the inductor, connected R3 and R4 to ground so the transistor can conduct, reduced the value of the collector resistor and added a base voltage divider and an emitter resistor so that the transistor is biased correctly.

It might or might not have enough range. The sunlight might cause the photo-diode to conduct all the time. The transistor has a low input impedance which reduces the level from the photo-diode and the transistor has a gain of only 22. The gain can be increased a lot if a capacitor bypasses the emitter resistor.
Usually a high gain and high input impedance opamp is used as an amplifier for a photo-diode.