Pages: 1 2 [3]   Go Down
Author Topic: IR frequency  (Read 2302 times)
0 Members and 1 Guest are viewing this topic.
Finland
Offline Offline
Sr. Member
****
Karma: 1
Posts: 270
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

If you are willing to lower the distance requirement a bit your project would certainly be doable. Wouldn't say 10-20ft suffice? Even 30ft could be doable if you use an IR diode that has high radial intensity.

Quote
How about 10 or more IR leds driven hard and installed at the far end of a long non reflective tube - I assume the non reflective tube will only emit a narrow beam ?

This wont give you a sharp narrow beam like a laser, but it would give you a narrow angle, i.e., the gun will be more like a shotgun than rifle.  But this is not necessarily a bad thing. The detector area in an IR detector is very small, a few millimeters in diameter. It would be very hard to hit the target if you really had a laser like sharp narrow beam.  Depending on the diameter and length of the tube, the beam diameter at the shooting distance could be an inch or two.  And I don't think you need 10 or more leds though. Try with a single led first.

edit: fixed a few typos
« Last Edit: June 22, 2012, 08:19:04 am by pekkaa » Logged

Offline Offline
Newbie
*
Karma: 0
Posts: 35
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Doc, I have utmost respect for a humble man who can admit a brief lapse in sanity.  smiley-cool  If you have an idea for me that will make the project more 'doable' then I am all ears (and eyes) and ready to learn.  I enjoy learning more from someone who is experienced than trying to read it from a book.

I'm not set on using the IR so if a laser would be easier then I'm all for it.  I do have several LDRs at my disposal.  A few came in my Arduino kit and a few I have salvaged from solar lights.

I do appreciate your help!
Logged

Finland
Offline Offline
Sr. Member
****
Karma: 1
Posts: 270
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Doc is certainly much more experienced than I am, but do yourself a favor an believe me in this case. Don't try to go with a plain LDR. Use a real IR detector, such as the one that Grumby_Mike suggested. If you go with a LDR, you will need a whole lot of additional electronics (noise filtering, amplifier etc) just to distinguish your signal from the ambient IR noise.

I actually built a couple of month ago something almost exactly like what you are going to build. I newer quite finished it, but I got the gun and the target working quite well. The shooting distance was about 10-15 feet. From that distance the IR beam diameter on the target was about 2 inches. (Depends on the length and the diameter of the gun's barrel.)

At first I experiment with a photo transistor. It kind of worked at night time, but at day time when sunlight came through windows, it didn't work at all. With an IR detector sunlight wasn't a problem.


* gun2.jpg (209.35 KB, 800x600 - viewed 18 times.)
« Last Edit: June 22, 2012, 12:08:48 pm by pekkaa » Logged

Global Moderator
UK
Offline Offline
Brattain Member
*****
Karma: 290
Posts: 25755
I don't think you connected the grounds, Dave.
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
If you go with a LDR, you will need a whole lot of additional electronics (noise filtering, amplifier etc) just to distinguish your signal from the ambient IR noise.
And it won't respond at anything like the frequencies commonly used (38kHz)
Logged

"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Anaheim CA.
Offline Offline
Faraday Member
**
Karma: 46
Posts: 2865
...
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Where, AWOL do you find 38Khz in a laser? that is a remote control carrier frequency that is OOK (On/Off Keyed) to be sensed by a device designed to detect the 38 Khz carrier and report the number of times it was on/off and the duration of each pulse... a waste of time as we aren't trying to turn on the target or change it's channel. As to the noise it really doesn't make a difference as it is much higher in frequency than the pulse presented by keying the laser on and off at a low rate, thus the incident lighting and noise can be essentially filtered / ignored. The laser light is coherent and thus is optically a lot more intense than ambient light and thus the ambient light can be largely ignored because we are converting the laser light into a pulse and detecting the pulse edge. The remaining issue is then the optical cross section of the detector and for that several LDR's in parallel would work nicely as the important thing is the rising edge of the change in resistance imposed by the laser light pulse. What about a red filter to pass the red and block much of the other impinging light. The current through the LDR's will set the detect sensitivity and or it might be readily possible to de-converge the laser light slightly so as to slightly spread the beam or better use a reflector to focus the laser beam onto an LDR. A simple flashlight reflector might well do the job of 'focusing' the laser light onto the LDR especially if the LDR was small enough to not occlude much of the reflector area or the reflector big enough to not be affected by the occlusion of the laser beam by the size of the LDR.... Simple.

Doc
Logged

--> WA7EMS <--
“The solution of every problem is another problem.” -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

Global Moderator
UK
Offline Offline
Brattain Member
*****
Karma: 290
Posts: 25755
I don't think you connected the grounds, Dave.
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

What sort of frequency were you thinking about to modulate the beam with (i.e. how are you going to immunise the system against DC light level changes?) and how well do you think a cadmium sulphide cell is going to respond?
Logged

"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Manchester (England England)
Offline Offline
Brattain Member
*****
Karma: 602
Posts: 33362
Solder is electric glue
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
or the reflector big enough to not be affected by the occlusion of the laser beam by the size of the LDR.... Simple.
Yes simple, it would simply not work.

Have you got any practical experience in this sort of thing? Your explanation sounds like a simple method that does not consider any of the practicalities.

The reason you need modulation for distance is that you need to amplify the signal from the sensor. This is normally a photo diode or photo transistor an LDR it totally useless in this situation.
If you amplify the signal from a sensor you are going to amplify the ambient light reading as well and quite soon the signal runs out of dynamic range and the amplifier saturates. So by using modulation you can simply AC couple into the amplifier and take out the DC offset bias.
Quote
Where, AWOL do you find 38Khz in a laser?
You can modulate a laser at what ever frequency you want.

Quote
a waste of time as we aren't trying to turn on the target or change it's channel
You can see from the above this is not true. It is a good idea to use TV remote parts because they are cheap and they do the job as good as anything else. Sure we are trying to detect the presence of a beam not send information to it, but it has to have the same characteristics as if we were trying to send it data.

What you seem to forget is that this is a gun trying to hit a target, not an IR blunderbuss trying to see if it is pointed roughly in the right direction.
Logged

Anaheim CA.
Offline Offline
Faraday Member
**
Karma: 46
Posts: 2865
...
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I have used red lasers from common pointer type devices in "Handgun" type holders chopper type drivers @ a 2 - 3 Khz repetition rate and successfully detected them with minor optical filtering ( a red led display filter over a CDS photocell [ldr] and I was able to detect the signal using a LM567 pll (8 pin chip) as a detector. While I realize that the part is probably pure unobtanium now I KNOW that it can be done... I've Done it. My first experiment (40 years ago) was a flashlight bulb (2 Ccell/3V) connected to ab AM radio and the volume high enough to keep the light bulb warmly lit (Not Full brightness and it worked with minimal shading of transmitter and receiver to drive an earphone salvaged (stolen) from a telephone set and an LDR in series with the earpiece and a 1.5 V D cell... Range was about 3 feet for good quality audio... BARE
All that need to be done is chop (pulse) the laser and amplify the received signal a little for detection. No REMOTE CONTROL DETECTORS NO 38KHZ... SIMPLE transmitter and simple receiver. Remember that even a small 1/4 watt laser puts ALL the power in the same direction and in phase (Coherent Light)... Low Power but coherent...

Doc
Logged

--> WA7EMS <--
“The solution of every problem is another problem.” -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

Global Moderator
UK
Offline Offline
Brattain Member
*****
Karma: 290
Posts: 25755
I don't think you connected the grounds, Dave.
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
Remember that even a small 1/4 watt laser
Remember also that a 250mW laser is really quite dangerous.
Logged

"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Finland
Offline Offline
Sr. Member
****
Karma: 1
Posts: 270
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

All that need to be done is chop (pulse) the laser and amplify the received signal a little for detection. No REMOTE CONTROL DETECTORS NO 38KHZ... SIMPLE transmitter and simple receiver.

But the 38kHz detectors are  simple receivers. You only need a capacitor and a resistor to connect the receiver to the Arduino.  It would be more difficult to design and build even the simplest amplifier as you suggested. And it is no more difficult the pulse an IR LED that a laser.
Logged

Anaheim CA.
Offline Offline
Faraday Member
**
Karma: 46
Posts: 2865
...
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Excuse me please I meant 2.5 mW not 250 mW... I also mentioned "Pointer type" lasers specifically and they can be controlled by the tone function to a driver/switch transistor... The torch or flashlight reflector works quite well too, place the sensor LDR OR Photodiode at the focal point of the reflector pointing in to the reflector. Part of the concept is to limit the field of view and noise like lights is in effect a dc change and can be blocked with a capacitor, the 60/120 Hz light 'flicker' can be dropped with a simple high pass filter and coupling capacitors. The detector just needs to see the 'tone' from the Arduino. We don't have a Blunderbus as the laser light is collimated well enough to hit only what it is aimed at. My comments re: 38 Khz refer to the sensitivity of the 'remote control sensor" they are deigned to work @ 38Khz with ook modulation... Not with a regular unmodulated beam. Yes the remote thing can be done and there are libraries to use the data... but all this thing needs to do is detect light and ignore room lighting, both easy tasks...

Doc
Logged

--> WA7EMS <--
“The solution of every problem is another problem.” -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

Pages: 1 2 [3]   Go Up
Jump to: