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IR transmitter comparison

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EOJ

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hey guys, I hope all is well. I have a question about the following two schematics. One is a high power IR transmitter and the other is a long range ir transmitter. When I look at them both I feel like they're doing the same thing just in a different way. Would I be correct to assume that they are modulating the IR signal? i see that they are pulsing the collector current to allow the highest intensity of light emitted as well. Is pulsing the collector current effectively modulating the IR signal? Thanks for your time.

long range: http://www.electroschematics.com/6114/long-range-ir-transmitter/

high power: http://www.electroschematics.com/3876/high-power-ir-transmitter/#comment-1530085
 

Nigel Goodwin

Super Moderator
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Same sort of thing, but the first one is poorly designed, you don't place the LED's in parallel, you put them in series as in the second one.

Neither of them modulate a carrier, they both just pulse the LED's ON and OFF.
 

MikeMl

Well-Known Member
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The net is flooded with poorly-conceived electronics sites created by inexperienced newbies. Electroschematics is one of those.

What are you trying to do?
Send Data?
Beam-Break detector?
 

EOJ

Member
Mike and Nigel, thanks for your response.

Nigel, we want series because we want a uniform current through each IR emitter correct? I guess I could alter the circuit and place all LEDs in series to mitigate the problem?

Mike, I am making an IR tracking system to track a free falling object. So my IR compound eye is my radar/sonar. I"m want to modulate the IR so the receiver can discriminate from the ambient IR in the room. I figured that pulsing a BD 140 will increase my IR light intensity hence increasing the IR transmit range. I guess I am a little confused on the difference between pulsing and modulating. I know what modulating is and its role in Comm, but am I doing both by only pulsing the BD 140? I'm not transmitting any data. What the receiver receives will be fed into a differential op amp which will go to a DC motor and "track" and moving object based on the amt of IR light received.

My plan is to modify the following circuit to increase it's range.
http://www.jameco.com/z/RS002A-Dagu...e-200Mm-Max-Reading-Range-Finder_2150441.html
I assume that this doesn't pulse nor modulate anything. If I did pulse a BD140 will there need to be a demod circuit to go with it? I don't think these IR receivers demod 38kHz like others do.

Can any one recommend any reliable schematic sites, come to think of it, I have a forrest Mims book maybe I should start there.

thanks again fellas!!
 
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MikeMl

Well-Known Member
Most Helpful Member
...
Mike, I am making an IR tracking system to track a free falling object. So my IR compound eye is my radar/sonar. I"m want to modulate the IR so the receiver can discriminate from the ambient IR in the room. I figured that pulsing a BD 140 will increase my IR light intensity hence increasing the IR transmit range. I guess I am a little confused on the difference between pulsing and modulating. I know what modulating is and its role in Comm, but am I doing both by only pulsing the BD 140? I'm not transmitting any data. What the receiver receives will be fed into a differential op amp which will go to a DC motor and "track" and moving object based on the amt of IR light received...
So you want to pulse the emitter at a fixed frequency so that you can build a more sensitive, ac-coupled, narrow-band tuned filter detector to provide immunity from sunlight?

If so, you are describing the system used for IR remote-control.

However, I do not follow how you propose to "track" a moving object. "Tracking" implies either measuring time-of-flight (by triangulation), or slewing (moving) a detector, like a rotating directional antenna, in order to discern direction.
 
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EOJ

Member
So you want to pulse the emitter at a fixed frequency so that you can build a more sensitive, ac-coupled, narrow-band tuned filter detector to provide immunity from sunlight?
Yes I would modulate at 38kHz or 32kHz, which is the standard used by most remote controls right? Based on the amount of IR reflected back would determine what direction the detector needs to rotate in order to maintain a zero difference across the inputs of a difference op amp. Does that make sense?
 

MikeMl

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Most Helpful Member
Yes I would modulate at 38kHz or 32kHz, which is the standard used by most remote controls right? Based on the amount of IR reflected back would determine what direction the detector needs to rotate in order to maintain a zero difference across the inputs of a difference op amp. Does that make sense?
Only if you have two detectors mounted so that their respective optical axes diverge, and you take the difference between the detector outputs. As the target moves relative to the detectors, there will a signed difference between the outputs such that goes from negative to zero to positive as the detectors are slewed with respect to the direction that the target signal is coming from.

See this post for an example.
You can use the ideas there to build a servo that slews the detector(s) to "track" a moving object. In that case, it was tracking the sun, which I dare say is easier than trying to track a rapidly-moving poorly-IR-reflective object that is illuminated from afar...
 

EOJ

Member
Mike you're the man, thanks for the link! Yeah I started to build a sun tracking solar cell as a some-what proof of concept.

Can you explain to me the detectors are "slewed" part? You're very knowledgeable, and I appreciate your input. Thanks again.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
My plan is to modify the following circuit to increase it's range.
http://www.jameco.com/z/RS002A-Dagu...e-200Mm-Max-Reading-Range-Finder_2150441.html
I assume that this doesn't pulse nor modulate anything. If I did pulse a BD140 will there need to be a demod circuit to go with it? I don't think these IR receivers demod 38kHz like others do.
Such designs are short range only, and not that effective anyway - and this one seems particularly 'poor' - you can't simply boost the power to the LED's and increase it's range.

Here's a 'better' design that I found on the net and used years ago, but again it's short range only.

http://lpilsley.co.uk/cybot/radar.htm
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
Moduation to me is the transmission of information.

A carrier is a means of modulation. so, that said, an IR transmitter that uses 38 k&z reduces it's power requirement by using a low duty cycle.

The IR LEDs get higher range by using higher peak currents.

You can turn the carrier on and off (sort of) to transmit information.
 

EOJ

Member
right on KISS, and Nigel. Nigel I'm going to build your circuit, along with others and compare. Thanks for the link.
 
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