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Discussion Starter #1 (Edited)
I'm going to try and build my own LED Lap Counter sensor assembly. Having never messed around with resistors and transistors (or even soldered ) before, I'm not real confident.

I started by buying the infrared LED's and infrared phototransistors from Radio Shack today. Same parts Greg Braun mentions using: 276-143 and 276-145. I'm already thinking the phototransistors are not going to work.

The plastic part is too large to fit between the rail and the slot on underside of track. So to use these, it appears they would need to reside in the table. Even if they would still be receptive to the light while 1/4" below the track surface, I think aligning these with holes drilled in the track would be a pain. It seems one would need to wait until the track is done and screwed down, and then drill through both track and table. Or, drill one (either track or table), and then use that as a guide to drill through the other, but again, once the track is all screwed down.

It's seems 100% better to have your phototransistors 'attached to' the underside of the track, so you can still fine tune your track positions. I read where Greg does not actually use these, and his site photos show a flat transistor that fits between rail and slot, so my experiment seems to confirm that he does not use these.

I think these transistors go back to RS....maybe the LED's too...and maybe, I leave this aspect of the track to those who know what they are doing, and just pay them for their skills.

.....but....I did buy a neat cordless soldering tool from RS!
 

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I considered this as well when using Greg Braun's Lapcounter 2000, but had the same problem with how deep the photocells would dwell. Since my track was to be mobile I had to rule them out, but your description is pretty much the same way he described on his website at http://www.hoslotcarracing.com/index.html. I finally had to go to the dead track method for my track, using the game pad USB port on my laptop. I only interupted one rail on my set up, since the switch involved the closing of the switch with the car istelf that was all that was needed.
 

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Discussion Starter #4
I've read that a dead track is popular for this, but before I go that route, I want to explore the other options (magnet switches and photo cells). I read in another forum were you have to be careful with a dead track, because you can accidently send voltage back to your computer and damage it. Granted, maybe you have to be a bonehead to make that mistake, but when I read that, I thought "Yep...that is what I would do...fry my Dell".

Even though the photo transistors I bought won't work for the track, I did go so far as to dig up an old parallel printer cable, cut off one end, and use a continuity checker to locate wires 10 and 25. I then twisted on one of the transistors, loaded LT 2000 on an old Thinkpad (my current laptop does not have any old-school ports), and I was able to register lap changes by moving my hand between the flashlight beam and the sensor. Whooo Hooo! It was a big deal for me seeing that work.
 

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The LED/PR fit is perfect on Tomy track but I see you have Aurora track. YMMV. If you have a piece to risk go ahead and try to drill it from the top. If it won't work you can always fill it with putty. This is not the kind of thing for a temporary track set up though.
 

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Discussion Starter #6
Franko said:
The LED/PR fit is perfect on Tomy track but I see you have Aurora track. YMMV.
My track does say Aurora on the bottom, but it is the Tomy track that you get in the current sets. I took those photo-sensors back to RS today. I found some flat ones on the internet, but have no idea if they are the right type to get. There is a fairly large electronics place near me, so I will take a piece of track in there, and hopefully they will understand the application (probably better then me) and have a sensor that does not have such a bulbous head on it.
 

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Im just curious as to what you read about the dead track section that can cause it to send power back to the parallel port. Did they say what specifically had to happen in order for the computer to get damaged? I havent found any other forums other than this one and the bench racers forum.
 

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I really think the RS LEDs will fit your track. Avoid gnarling up the plastic in the track slot but don't worry about it beyond that. I think I remember it is a tight but neat and clean fit. Use the size drill bit recomended on Braun's website.
 

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One thing I dont fully understand is how the photo emitter works. So theres a photo cell transistor mounted under the track and you need a bright light above this track section. And when the car passes over the light it blocks out the light and triggers the signal to count the lap time. Is that correct? Im getting ready to wire up my setup to give it a test but I needed to understand the theory and logic behind this first.

Also, what part of the photo sensor needs to be in the light path? I have the round LED looking photo cells and had planned to just stick the tip of the photo cell thru the track but after reading more Im not sure it will work. I could always ghetto wire it and try it with the software. But Im starting think the insides of the emitter need to catch the light. Any thoughts on how the photo cells work would be helpful. I dont mean to hyjack Jeff's thread but its on topic.
 

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Discussion Starter #10
I was also having trouble understanding how they worked. It wasn't sinking in just reading all the great info on the site. Not till I just bought some stuff and tried it did it start to click. If I have anything wrong here, I hope someone advises.

Here are some things that confused me, and how I now understand it.

The Light Above

The light above the track is just simply, a light. The light in the ceiling of your room could conceivably serve the purpose, but the problem is it would be easy to block that light; with your body, and arm, etc. If you block the light, the transistors below the track could sense the loss of light, and send a signal to your computer that another lap was made by a car, or all cars.

So people put a light just above the track. Some people use a small flourescent light, or maybe even an irradescent, and they build a structure simply to hold it above the track. Then, you just need to power it. If it is a 120v light, plug it into a wall socket. If it is a light that uses a wall-wart, plug it into your power strip where you have your other wall warts. But since you have 18vDC right there on your terminal blocks under the track, it would be benificial to use a light that can get power from that source.

Some people don't want this bright light shining down on this small portion of their track, so they use infrared lights, since our naked eyes do not see the infrared light waves. These small infrared lights that can run of low DC voltages need to be directed fairly accuratly to the sensors below the track. That is why they use 4 lights, one above each track. It's not that you need a seperate light per lane, but it is the best way to make sure you get light down to each sensor.

The Sensors Below

These are the things that actually sense the cars going over, and send the signal to the computer to register a lap. When the light beam they are normally seeing get's broken, even just by the fraction of a second of a car passing over, they send a signal to the computer.

The bulb-like transistors I bought at Radio Shack seemed to not care if the light was coming at them from on their dome top, or from the side. I could hold the wire with a sensor on it in one hand, flashlight under my chin, and wave my hand between them and the Lap Timer software registered the lap.

The problem with my transistors and the track is that they don't fit, or maybe, didn't fit like I thought they should. And that is when I read that there are other, flat transistors that will fit better under the Tomy track. These transistors do have a sensing side and a non-sensing side, so you do have to mount them proper side up.

The attached photo is from hoslotcarracing.com, and shows the flat ended transistors.

Hope this wasn't too basic, or too complicated...or worse...all wrong. :)
 

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Discussion Starter #11
PS: I found a part number for a flat sensor at another slot car website. Honeywell Part# SDP8436-003

I found the part at Newark.com

Here is a link:

http://www.newark.com/jsp/Optoelectronics,+Lamps+&+Displays/Optocouplers/HONEYWELL/SDP8436-003/displayProduct.jsp?sku=59K0256

I'm not sure though that it is correct for our purposes.

I also found this one at mouser.com

http://www.mouser.com/search/ProductDetail.aspx?R=OP550Avirtualkey54210000virtualkey828-OP550A

But, not sure if it is correct for us. Looks like the Honeywell one above, if you check out the datasheet.
 

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Hello,

I used Mouser to get my IED and Phototransistors. These are close in wavelength and a T-1 package which is the smallest right now for what we need. I made my own lightbridge using vinyl siding channel and matched the IEDs above the phototransistors in the track. I do not have the power to post a pic

OP506A Optek Infrared Phototransistors
OP166A Optek Infrared LEDs

If you use a 9 volt wallwart put in a 270 ohm resistor
12v use a 560 ohm resistor

This way you will not have the distracting lamp while racing.
 

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I have the rounded top RS sensors mounted from below in tomy track. The four sensors are mounted between a power rail and slot of each lane and are raised flush to the level of the track and work great.
 

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Tyco track doesnt leave any room to mount something below the surface w/out some grinding action. Jeff, I understood everything you said and it confirms what I already assumed. So I think Im going to continue with the same game plan and hope it works out. Im not going to get into infrared or LED's, most likely I will find some cheap alternative to mount a bridge with lights uderneath it to provide the light source. I just think its easier to have a single light source for all the phototransistors than try to get all the LEDs or infrared beams lined up. To each his own, as long as it works!
 

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Trakmate comes with the 3mm sensors. I can't remember what the part number is that Greg lists on his website but I'm pretty sure I used those larger 5mm ones on another members trak with the freebie timing program available from Greg Braun. We installed them in Tyco track without a problem. Try not to let the head of the LED extend past the track surface or it can be scratched and rendered unreliable.

Unless you understand LED's and electronics well, those sensors you're using may cause frustration. I've never seen anyone use those before. The ones listed by racers from Radio Shack are proven to be correct for most lap counter software and overhead light sources. Most LED's list the range of use on the back of the package.

Oh ya- you'll need to mount the sensors to the bottom of the track, not the table. You don't want any shadows cast on the sensors if they sit too low or off-center of the track holes.

A note on timing software; what it actually does is measure the amount of time the object disrupts the light source in front of the sensor when the light beam is broken. That measurement is then converted to various outputs and written to a scale speed/lap time that is appropriate.

Scott V.
 

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Hello. One question about the Photcells: Will the 'infrared' sensors require 'infrared LED's or will simple room lighting or standard white LED work? Thanks! Any advice would be grreatly appreciated. :)
 

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Discussion Starter #17
The specs on the photo-transistors I found on the internet list what type of light they will react to, and all the ones I saw that include 'infrared' also included many other types of light. While I guess they might manfacture a photo-sensor that only reacts to infrared, I think it is safe to say that an infrared sensor will react to many light sources, including an infrared light source.

The infrared-capable sensors I picked up at Radio Shack reacted to my normal flashlight.
 

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I'm new to the forum and have remained a spectator, but I felt compelled to make this my first message.

I bought the RS components and followed the directions on Greg Braun's site. I tried to get the serial (COM) port wiring to work, but I had no luck. I got the parallel (LPT) port wiring to work during bench testing.

You are right about the photo transistors; they don't fit too well between the slot and rail. I drilled the largest holes possible, but the sensors still hang below the track. I'm not going for a permanent layout yet, so I will have to elevate the track at this location.

The IR LEDs are necessary if you don't want to place a bright light source above the photo transistors. I bought a HO pedestrian bridge (Bachmann/Plasticville) to incorporate the LEDs. The LEDs must be mounted fairly close (2-3") to the photo transistors.

I have yet to test this under race conditions, but have spent a considerable amount of money and time experimenting with the right setup. Having gone through this, I would strongly recommend buying the whole thing from Greg's site. I'm sure others out there have had better luck, but that's my perspective.

Good luck
 

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Hi 13013comstock, I built the cable (old joystick cable and a cat5e ethernet cable) pretty cheaply($) I had some 3mm photoresistors I picked up from an ebay store but tried the IR's first and concluded they will need alot of lighting. The 3mm ones will fit much better Im thinking of taking some .02 to .03 styrene a half inch wide and the width of the track with holes drilled to attatch the PR's under the track. Ill either elevate the track there or clear out underneath for wiring clearance. Also Im just going with the pedestrian walkway LED gantry that will be battery op'd, with a small on/off switch.
 
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