IR Receivers and Continuous Signals

[remiller]

I want to built a circuit that can detect objects using a 38 kHz infrared signal and have been able to create the emitter, but I'm having a hard time with the detector. I recently found out that it is because the type of IR receiver I was using requires the 38 kHz signal to be sent in bursts. As I am relatively new to electronics, I would like to keep the circuit simple. Is there a receiver available that will detect a continuous signal?

 

[shaneshane1]

im fairly new to this stuff as well but i had a similar problem, if you use a simple anode cathode receiver it will work but the range wont be as far and sun light and room light will affect it as well

 

[remiller]

Thanks, shaneshane. The sensitivity to sun light and room light is one of the things that I would like to avoid, but I may try this.

 

[audioguru]

The IR receiver ICs have an automatic gain control that reduces the gain when there is interference at the frequency the IR is modulated at. Modern compact fluorescent light bulbs create IR interference continuously at about 40kHz so the AGC in the IR detector IC reduces the gain when this kind of continuous interference or continuous signal is received.

 

[Ambient]

Actually I am dealing with this same issue for my senior design project. We need to keep track of which of 4 IR detectors is getting the most signal from 1 detector.

The ballasts for Fluorescent lighting are supposed to operate above 42kHz. But some operate from 20kHz to 30-something kHz range. You can make a narrow bandpass filter. Texas Instruments has some documentation that gives some active filter schematics. Do not bother with the IR detectors that are designed for data transmission. Those detectors have a filter but also have a comparator that is sensitive enough to pick up IR bounced off of a wall.

 

[remiller]

Thanks for all of the helpful hints. Maybe I will give the simple anode-cathode receiver a try with a narrow bandpass filter. If I set the filter well below the frequency of normal flourescent lighting balasts, I should be OK - yeah?

 

[philba]

why go to all that trouble? AGC is your friend. I'd just use a 555 to generate a gating signal. then you can create a stream of bursts with your IR codes.

 

[remiller]

So it would be more trouble to create a narrow bandpass filter, than to send the 38 kHz in bursts? Would I need to use a 556 to allow for the pauses between the series of bursts?

 

[philba]

you could use anything to create the timing of your bursts. a 556 is just a dual 555 so yeah, that would work. You don't say how you are generating the IR pulses in the first place. that would be helpful.

bandpass isn't terribly hard but then you lose AGC which is very nice for the kind of environments you might encounter.

 

[huttojb]

Can I ask what the project is for?

Jason

 

[remiller]

The reason I mentioned the 556 is because I see a lot of datasheets for IR receiver ICs that have indicated that there need to be pauses in between bursts of the IR signal. I am currently using a 555 to generate the 38 kHz. In total, it seems that I would need one timer to create the correct IR frequency, one timer to pulse the frequency, and one timer to create spaces between the series of pulses.

This is for a robot I am trying to build. I would like to bounce an IR signal off of an object about 1 foot away to detect obstacles. I have seen examples of such circuits in books and on-line, one of which used an IR receicer IC (PNA6402M). However, it is unclear as to whether or not I need to transmit the 38 kHz IR signal in bursts to activate this receiver, or if it will detect a continuous signal. Nothing too spectacular, but, like I said, I am still new to electronics - so whenever I get anything to work, I am very pleased with myself!

 

[gramo]

This bad boy can detect objects from 0-6.45 meters away with a 2cm resolution 20 times a second

It has 3 ways of interfacing with it;

# RS232 Serial Output - 9600bps
# Analog Output - 10mV/inch
# PWM Output - 147uS/inch

https://www.sparkfun.com/commerce/product_info.php?products_id=639

 

[gramo]

Its ultrasonic though. Perhaps its no good for your application

 

[remiller]

A good thought. I think it would work fine for my application, but I feel like I wouldn't be gaining the same type of experience using pre-fab circuits, as I would if I were building everything from scratch. As much of a thrill it is to get something working, I would like to have a good understanding of all aspects of the circuitry. I appreciate the recomendation, though. This may be something that I use later on.