Timer Schematic, any thoughts Laser Pointer

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dguy
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Timer Schematic, any thoughts Laser Pointer

Post by dguy »

Hello all,

http://www.geocities.com/turbo_doggie/image/timer3.pdf
(COPY & PASTE INTO INTERNET EXPLORER TO SEE !)

I tried to use IR LED's & IR photodiodes bu whne I got more than 2" apart I notices that the transistors were not in saturation anymore.

I then tried a laser pointer and it worked from many feet away, with the same photodiode.

I built my finish gate I drilled 1/2" holes in the top and oversized them a little. I Then drilled 1/8" holes in the bottom for the photo transistors. I used (4) bullet laser pointers from Ebay ~ $12.50 including shipping. I decided to use a pattern lens which caused the laser to spread a little.

The lasers were modified by using a dremmel tool and cutting a hole in the case just opposit the power switch. A wire was soldered to the PCB here and I sanded off the paint on the outside and used a hose clamp to attach the (+) wire.

Then with the lasers turned on at 3.6 V I epoxed the lasers in place.

Caution. The Lasers were made to run on (3) 1.5 V batteries, turning up the voltage can make the lasers dangerious, and burn them out quickly. That is why I backed down the voltage at 3.6V I found the beam was strong enough to be visable and to saturate the photo transistor.

The other adjustment I did was on R10 this I set at 1.8 V, it seamed to go from 0.3V when the laser hit it up to 4.9V in rather strong ambient light. This may have to be adjusted lower to work outside. I would however reccomend that the phototransistors be shaded from direct sunlight to work properly.

I have not used this system in competition yet, does anybody see any adjustment that may be needed ?

Thanks,

David
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Re: Timer Schematic, any thoughts Laser Pointer

Post by gpraceman »

dguy wrote:I tried to use IR LED's & IR photodiodes bu whne I got more than 2" apart I notices that the transistors were not in saturation anymore.
That is a bit suprising. Maybe you were using too high of a resistance to control the current on your IR LED's. I have no problem with mine, up to at least 6". I'm using the IR LED's and photosensors that I got from Radio Shack, and they have worked well these past five years. To me using laser pointers are too expensive and power hungry for this application.
Randy Lisano
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Awana Grand Prix and Pinewood Derby racing - Where a child, an adult and a small block of wood combine for a lot of fun and memories.
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Re: Timer Schematic, any thoughts Laser Pointer

Post by terryep »

I use an 8" separation using only 10mA of IR LED current on my Fairchild devices. My three lane track runs on 2 AA batteries for 65 hours.

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Re: Timer Schematic, any thoughts Laser Pointer

Post by dguy »

Thats interesting:

I used Panasonic
a) photo transistor #PNZ108
b) IR LED # LNA2801L @ up to 50 mA of current.

My incandesent light was detecting more than the IR source was detecting.

David
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Re: Timer Schematic, any thoughts Laser Pointer

Post by terryep »

Try the QSD123 phototransistor, and QED123 IR LED both available from DigiKey http://www.digikey.com/ These have only an 8 degree pattern so you need to align them carefully.

Terry
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Re: Timer Schematic, any thoughts Laser Pointer

Post by John Shreffler »

A laser is definitely overkill, unless money is no object.

Small correction on Randy's reply. You get more separation by going HIGHER on the photodiode resistor. There is a tradeoff, the emitter remaining constant: The higher the photodiode resistor, the greater the sensitivity, but the slower the response. Also, the greater susceptability to ambient light which contains IR. I use 22K ohm in The Judge, as a reasonable trade-off between the competing parameters. This gives a typical maximum separation range of 6 inches, and 20 microsecond response. Of course you can put more power into the emitter, and gain separation, but this is at the expense of battery life. The Judge emitters are running at 10 milliamperes.

Go for the most sharply focussed emitter you can find. There is a wide range of focus for various applications. For pinewood, tight is right. Even the tightest focus is still broad enough to make alignment a non-issue.
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Re: Timer Schematic, any thoughts Laser Pointer

Post by John Shreffler »

Oooooops, correction. I just re-read Randy's comment, and saw he was talking about the IR LED resistor, not the photodiode resistor. Sorry, Randy.
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Feedback - raceday and more questions

Post by dguy »

Hello,

Well today went ok. But I did have a problem. The laser pointers were cheap and the out put one one laser first had a drastic rediction then quit all together. This was despite running only 3.6V (not 4.5V). I guess this type of stuff made in China is just not good enough.

Since the Laser pointers required carefully removing a peice from the side wall and soldering a wire to the PCB. I also had used epoxy to mount the laser the and the alignment was not too difficult but the laser was impossible to replace on race day.

Neadless to say we raced on 3 lane on a 4 lane track.

The use of the LM339 did help as I was able to adjust the sensitivity of the sensors. I did end up reducing the resistance on the sensors from 100K to 3.3 K because they were way to sensitive with 100K.

Once I take out the lasers I think that I may have to increase the resistance I think that I will try 22K like John reccomended.

I saw another article that someone just used superbright Red LED's and there was enough sensitivity for the sensors to this wavelenght. What are your thoughts ?
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Re: Feedback - raceday and more questions

Post by terryep »

dguy wrote:I saw another article that someone just used superbright Red LED's and there was enough sensitivity for the sensors to this wavelenght. What are your thoughts ?
IR LEDs are your best bet. If you work in the red you will be more susceptable to room lighting and flash photography. IR LEDs are also much brighter than Super bright Red LEDs.

Use matching IR photodiodes with visible light filtering.

Terry
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Re: Timer Schematic, any thoughts Laser Pointer

Post by chipcoder »

Interesting - I'm building a finish line gate and had the exact same thing happen. It worked at above 5 or so inches out in the open on my bench, but not reliable at 6 inches.

When I imbeded the sensors in the track and the LEDs in the bridge, my range dropped down to 2 inches or so. Swapping out for super bright red LEDs didn't help either (but it looked really cool). I was able to bring my range back to almost 4 inches by increasing the resistor on the sensor from 10K to 20K. Anything above the 4 inches and it quits working again.

It's not an alignment issue, I've eliminated that. My sensors are oriented correctly (emitter & collector). I'm using Radio Shack IR components also with my LEDs at about 20ma, 5V supply. Other's have claimed 6 inches or so with these exact same components - I don't know what I'm doing different. Could it be the size of the holes in the track? But even out in the open I don't know if I'd trust it at 5 inches.
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Re: Timer Schematic, any thoughts Laser Pointer

Post by terryep »

Are you using clear photodiodes or ones that look black? The black ones have daylight filters on them where red LEDs won't be very effective.
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Re: Timer Schematic, any thoughts Laser Pointer

Post by chipcoder »

The plastic is clear, so it's not that
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Re: Timer Schematic, any thoughts Laser Pointer

Post by terryep »

Is it possible you overdrove the LEDs at some point? LEDs get dimmer before they die, I'd get another LED and hold it above the one in the track and see if it works as you approach the PD... bad solder joint? You can measure the voltage across your balast resistor to verify 20mA....
Terry
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