IR Sensors- will they attack hot Chiaphuas?
 

Scenario- it has been a long hard day and your Chiaphuas are too hot to touch- its the elimination rounds

what will an IR sensor home in on? A light bulb 20 feet away or your neighbors drive system 5 feet away.

Now that might be a real Frenzy- when robots attack!!

Just a thought......he he
:cool:

WC

Re: IR Sensors- will they attack hot Chiaphuas?
 

I had a similar question: What about all of the other IR interference that comes from the cameras and camcorders in the stands. What about the Media who bring cameras and video cameras into the area right around the outside of the field? What about the cameras that feed the big screen?

For those of you who don't know, the auto-focus on your camera relies on an IR signal being bounced from the camera to the object and back. This tells the camera the focal point.

Will we see robots attempting to leave the field to attack the media? Or, has FIRST put the IR on a different frequency or spectrum (I don't know if this is possible)?

Re: IR Sensors- will they attack hot Chiaphuas?
 

From TheArena, 3.2.5: "Each beacon emits at the same IR frequency, but sends pulse trains of different widths.... FIRST has supplied appropriate code that allows teams to program their robot's controller to make decisions based on a received signal and discriminate between the two Tee locations."

The beacons are not just a flashlight IR source, they send a modulated signal on a particular frequency. Robots using the code should be able to ignore most IR interference - though IMHO, testing with interference would be a good idea. I notice the humans were careful to stand far far away from the demonstration 'bot ; ) -Piece, Pteryx

Re: IR Sensors- will they attack hot Chiaphuas?
 

These IR sensors detect light not heat so there isn't a possibility about them being attracted to another robot or something hot

Re: IR Sensors- will they attack hot Chiaphuas?
 

Thank you for pointing this out! I don't know the answer, but
at some point I'm definitely going to ask the filmmaking people at my college to bring in some cameras so that we can test this.

This is my first year as a team leader and I feel a little like the guys on Apollo 13. There's a line from the movie where one of the astronauts (Swaggert I think) is concerned that they will overshoot the Earth. Lovell replies "there are about 1000 things that have to happen for us to get home. We're working on number six, you're worrying about number 520." Its just one more item on the giant list of things to worry about :)

Re: IR Sensors- will they attack hot Chiaphuas?
 

One other thing I've thought about. What about the Night Shot on some camcorders such as Sony. Are those IR devices? Even though you wouldn't be using it at a competition, could someone use it to knock a robot off it's course?

Re: IR Sensors- will they attack hot Chiaphuas?
 

To put it simply THE INFRARED SENSORS WILL NOT DETECT ANYTHING OTHER THAN WHAT THEY HAVE BEEN DISIGNED FOR! ie. AN INFRARED EMITTER EMMITING AT THE FREQUENCY THE INFRARED DETECTOR HAS BEEN SET AT. I worked for 3/4 years designing and programing a pinewood derby racetrack finishline that uses infrared. We have not had any problem with extra light or other types fo thigns that interfere.

Re: IR Sensors- will they attack hot Chiaphuas?
 

Re: IR Sensors- will they attack hot Chiaphuas?
 

IR is a form of light beyond the range of human vision but it is a form of radiant heat. My question is- does a heat source emit a specific wavelength or a broader spectrum of wavelengths including the ones sensed by the sensors?

Second scenario- the processors of the sideline computer control station emit a heat source or maybe have IR networking.

It would be fun to see all the IR sensors in the arena make a beeline for the control team. A real frenzy- who can hit who first- the robots take out the controls or the operators hit the stop buttons.

I'm sitting way up in the stands this season...
WC :ahh:

Re: IR Sensors- will they attack hot Chiaphuas?
 

Ok, you should experiment with infrared sensors and a detection card to see what it does. These infrared emmitters and detectors OPERATE AT A SPECIFIC FREQUENCY. Thus the emmiter (on the sideline above the balls in the center) does bursts of light, on and off repetidly at a certain speed. simmilar to your TV remote. you cant take any remote and make it work with your TV it MUST be on the correct frequency.

Just believe me, the robots WILL NOT go for heat.

by the way. it would NOT be fun for a robot to take off after a control table. note the words CONTROL TABLE. if this happened it would take time to fix everything.

Re: IR Sensors- will they attack hot Chiaphuas?
 

Don't you every year Wayne?
Get some sleep, you are getting goofy already :)
Have that 9 ft arm built yet?

Re: IR Sensors- will they attack hot Chiaphuas?
 

40khz is the wavelength at which the beacons will be transmitting (I'll find the quote in the manual later). If I ma not completely mistaken, that is on the high end of the infared spectrum, just below the visible spectrum, so for someting to emit infared light from being hot, it would need to be REALLY hot, and i think most CIMs will die before getting that hot.

Re: IR Sensors- will they attack hot Chiaphuas?
 

It depends on the quality of the sensor really. I have experimented with building a LIRC-style universal IR receiver once and I can say that some detectors are actually affected by direct sunlight and fluorescent lights. Others are not affected as much. However, even if this does happen, the demodulated data is garbage, and will never be equal to the signal sent out by the beacon. So the robot will more than likely never consider a camera or a hot motor a beacon. However, strong interference may not allow a bot to recognize a beacon. This should not be a problem, however, since the playing field is usually quite dark.

Re: IR Sensors- will they attack hot Chiaphuas?
 

if it is a problem, you can get some aftermarket IR sensors that give back an analog signal, not just YES/NO. Then you can figure out what is strongest and most likely the beacon. And if you have a good programmer, with sensors attached to servos, he can make the bot check to make sure the IR it is detecting is comming from the right direction relitave to your starting position.

Re: IR Sensors- will they attack hot Chiaphuas?
 

I dont think this is possible. As has been said before, the signal is modulated. It is not just a "light on/light off" thing. The beacon is likely sending out modulated binary data, and the receiver gets the pulses, demodulates them, and then the software compares the binary signature. This is how a TV remote works. An analog detector would just get the average brightness of a pulsating source. Of course, all of this is unconfirmed - I have not seen the code yet and all the IR stuff is missing from our kit :(

Re: IR Sensors- will they attack hot Chiaphuas?
 

ahh, good point. I'm used to constant signals, but who knows? I think some experimenting is in order. Maybe some interrupts to collect the strength for 2 ms... hrmmmm

-Kesich

Re: IR Sensors- will they attack hot Chiaphuas?
 

Wouldn't these things be as realiable as the sensors from last year we used to detect the reflective tape? I think they worked the same way.

Re: IR Sensors- will they attack hot Chiaphuas?
 

Didnt those use the visible light spectrum? And the light sensors projected, whereas the IR sensors just pickup, so there really isnt the chance of seeing reflection when there isn't one. I went straight dead reckoning, though. Getting to the top of the ramp and hitting boxes in 5 flat seemed better to me. Anyways, in the line vs IR arguement, i'd say IR because you can see the IR from anywhere. The line, on the other hand, can get smugged up, lost, and once you are done with it, the sensors are useless. Ir can triangulate though.... hehehe

-Kesich

Re: IR Sensors- will they attack hot Chiaphuas?
 

The signal from the beacons and receivers probably resemble the signals from a television remote. I have never encountered any interfernce from body heat on those things.

Re: IR Sensors- will they attack hot Chiaphuas?
 

Wouldn't that be funny. Walk by the TV with a candle and the tv turns on, mutes, unmutes, cranks the volume, then hacks the cable box and gets you free PPV for life. Heheheh :-D

-Kesich

Re: IR Sensors- will they attack hot Chiaphuas?
 

20 ft.....

Re: IR Sensors- will they attack hot Chiaphuas?
 

What I meant about last year's sensors is that they sent a specific pulse pattern to prevent picking up sources other than itself. Although my team didn't use them, I played with the sensors and found them pretty reliable. I dont think we have to worry about someone accidentally confusing the robots with a camera or furby.

Re: IR Sensors- will they attack hot Chiaphuas?
 

The IR Sensor is set to only detect the frequency emitted from the beacon. Similar to way your TV remote works, you won't get out side interference.

Re: IR Sensors- will they attack hot Chiaphuas?
 

OK,
Before you guys get too crazy, the IR emitters generate energy in the same area as heat but have one distinct difference. The emission will occur as 40kHz pulses for varying lengths of time. That is, bursts of 40kHz modulated IR energy. The night illuminators on cameras are just that, steady state, non modulated sources the same as hot bodies. The IR camera range finders and remote controls use modulated IR emitters at different frequencies so there should be no real problems if you keep in mind that you are looking for a 40kHz modulated source. The bandwidth of the IR is not 40kHz but likely is much wider than that since the bandwidth you are measuring is near visible light.

Re: IR Sensors- will they attack hot Chiaphuas?
 

Too late :).


Yes, as Al correctly (again) points out, the Vishay TSOP4840 sensors that are included in the kit and also used for the kick-off demo specifically discriminate against these type of energy sources. They also discriminate against non-modulated 40KHz sources. I've put a link to the data sheet here: http://kevin.org/frc. The modulation scheme is discussed in this thread.

-Kevin

Re: IR Sensors- will they attack hot Chiaphuas?
 

this is something that i asked about at the main kickoff because of the fll problem. the guy told me that he tested the ir sensors with 5 cameras that were said to have problems with the fll bots and none of them caused interference. he also mentioned that these ir sensors are the type used in high-end stereo equipment and the only thing to possibly worry about would be a flickering flourescent bulb.

Re: IR Sensors- will they attack hot Chiaphuas?
 

Kevin,
Thanks for the pdf, I am forwarding it to our electrical guys right now. Good info in the data sheet, too!

Re: IR Sensors- will they attack hot Chiaphuas?
 

yikes! 40 khz is not a wavelength - it's a frequency - and I don't think it is the frequency of the electromagnetic radiation coming from the source either. If that were the frequency, the wavelength would be about 10,000 meters. That's a real long radio wave, not infrared. So, yes, you ARE completely mistaken. Perhaps the infrared source is being pulsed at 40khz, but that's a whole difference animal. :D

Re: IR Sensors- will they attack hot Chiaphuas?
 

How many pulses must the sensor receive in order confirm which beacon it is seeing, and therefore, how fast can the sensors sweep the field and still detect the beacons?

And a less important issue, will the beacons appear as bright lights on videos of the matches since many camcorders are sensitive to IR light?

Re: IR Sensors- will they attack hot Chiaphuas?
 

You don't really have to worry about how many pulses they need to see. at 40khz, this will not even be an issue. You can basically assume the response is instantaneous.

yes. Some cameras more than others. It will show up as bluish white. Point a TV remote into your camera to get an idea of what i mean. You can prolly find IR filters if things are really bad.

Re: IR Sensors- will they attack hot Chiaphuas?
 

Just to make it clear, these sensors use near-IR, which means the light they use has a wavelength somewhere between 0.75 and 1.25 microns. Thermal IR, on the other hand, has wavelengths of between 3 and 30 microns. Heat will not be a problem.

Also, interference will probably not be a problem. The beacons (like most IR devices) emit bursts of light of varying length, which they use to send a coded message, similar to the way morse code can be used to send a text message (I am not certain what coding scheme is being used, but there are many commonly used including NEC, Sony, Toshiba Mincom, RC2000, RC5, RC6, IrDA, etc.). The Robot Controller can be programmed to look for this message, and if it isn't what it is expecting, ignore the signal.

Furthermore, each burst is not actually a solid burst of light, but is chopped up so that when the beacon is bursting, it is actually flashing 40,000 times a second. Inside each detector, a circuit called a bandpass filter removes all signals coming from light that isn't flashing near 40,000 times a second. Since most IR devices don't operate at 40kHz, most signals will never even make it to the Robot Controller.

Re: IR Sensors- will they attack hot Chiaphuas?
 

Al pretty much nails it. The whole modulation thing can be tricky for anyone who hasn't seen it before, so that's probably the big cause of confusion (ie, IR frequency != 40KHz).

However, it should be noted that nearly all (I think it's all) TV/Stereo remotes operate at 40KHz (it's actually just a shade off). Most off the shelf commercial IR sensors (ie, the kind you buy at Radio Shak) only look for this 40KHz signal, and filter everything else out. The way your TV, and your FIRST robot, know the difference between the signals is in the coding scheme used on top of that 40KHz carrier. So... if you go off and write your own code, yes, TV remotes could be a source of interference. Or, perhaps cooler, you could probably allow (for demo/debug purposes) the FIRST controller to use a TV remote as an input, provided you knew the coding scheme of the controller (you can find many of these online).

Something I haven't seen made mention of yet is multipath interference*. I worked on an IR project a few years ago and would get strong multipath interefence when I was transmitting near large metal objects (in this case, lockers at the HS we were working with at the time). I'm interested to see if this becomes an issue, especially as one or more robots approaches the beacon. I'm not sure if this will be a major issue (I suspect not, but it could be depending on robot geometry), but the fix should be simple enough if it is.

* multipath interference - in short, when you recieve a signal that has been reflected off a few objects before you receive it. for example, in a car radio you have a direct path (radio tower to you), and a ground bounce path (tower, ground, you) - mutliple paths, hence multipath interference. In our example, this means that robot reflecting IR waves from the beacon appears to be a source, potentially causing problems for your location algorithm.

Re: IR Sensors- will they attack hot Chiaphuas?
 

Multipath is a degradation of signal due to a reflected signal arriving with the direct signal at a receiver. When the reflected siganl is far enough apart that the reflected signal is 180 degrees out of phase and near the same level as the direct signal, the two cancel out. Obviouosly at the frequency we are interested in (the IR frequency not the modulation 40kHz) there can be several objects on the field that will produce reflections that are 1/2 wavelength or multiples of 1/2 wavelength giving the out of phase condition.

Re: IR Sensors- will they attack hot Chiaphuas?
 

I thought about that source of interference as well, but at these wavelengths very slight differences in distance will result in going from constructive to destructive interference (and back). I figured that then on average the chances of a missed detection are probably pretty slim. That brings my main concern back to the stray signal problem.

We have essentially a Direction of Arrival (DoA) problem - for more info just google for more info, or search IEEExplore if you have access. A similar problem has been solved many times over, especially in test ranges for antennas and radars. They have essentially the same problem we do - you can't distinguish a reflection off a wall from a reflection from the object. Now those guys use some pretty fancy techniques to eliminate those issues, but we can take a page from their notes. Since we have a priori knowledge of the source location (something I didn't have in the example I cited previously - in that case my beacon was moving), we can ignore signals coming from regions we don't expect to see on in. Now, this brings up some potential navigational pit falls, but if you used IR search/track in combination line following you'd be in good shape. If you're just randomly searching for a beacon then stray signals *could* become an issue. It's hard to say for sure (especially for me to say since I'm an EM guy not an E/O guy) until somone tries it out. However, since again the potential source of the stray signal is moving (quickly with respect to wavelength), this might go away just like the true multipath problem.