# Photo Cell Sensors for Lap Counters



## Scafremon (Dec 11, 2006)

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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## SwamperGene (Dec 1, 2003)

Hi ScafremonCheck your PM's, I may be able to help you.


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## Pete McKay (Dec 20, 2006)

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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## Scafremon (Dec 11, 2006)

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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## Franko (Mar 16, 2005)

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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## Scafremon (Dec 11, 2006)

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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## BewstdGT (Jan 4, 2005)

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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## Franko (Mar 16, 2005)

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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## BewstdGT (Jan 4, 2005)

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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## Scafremon (Dec 11, 2006)

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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## Scafremon (Dec 11, 2006)

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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## BBailey (Dec 4, 2005)

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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## Franko (Mar 16, 2005)

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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## BewstdGT (Jan 4, 2005)

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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## Slott V (Feb 3, 2005)

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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## MaximuM (Jan 31, 2007)

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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## Scafremon (Dec 11, 2006)

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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## MaximuM (Jan 31, 2007)

Many thanks!! I have the same sensors and I'm sure they will work fine. Thanks again! :thumbsup:


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## 13013comstock (Nov 25, 2006)

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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## MaximuM (Jan 31, 2007)

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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## Craig Jorgensen (Nov 21, 2004)

I built a track a couple of years ago and used Greg Braun's setup, purchacing the stuff at Radio shack, and after quite a bit of dinking around, finally got it to work reliably. I sold that track to a friend, and it still works great, in fact we used it last night. In the mean time, I built another track, and again used Greg's setup, but I couldn't get it to work properly to save my life. I kept switching LED's, power supplies, wires, etc. Nothing but mistriggers. I even bought all the parts from Greg and I still couldn't get it to work. The problem was getting enough light on the LED's, If I used a bright spotllight, or flashlight it worked fine, but not with the IR emitters. So I gave up and bought the setup from Trakmate. Worked first time, every time. I think I know why. I took an infrared photo of the two emmitter gantrys side by side while they were powered up, and the Trakmate is at least 10 times brighter. Nothing against Greg, he's just trying to provide something easy to make using commonly avialable parts. The problem is that Radio Shack stuff is junk. So's that cordless soldering iron, which I'm sure you found out by now!


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## sed6 (Feb 21, 2007)

I found these IR sensors the other day looking through the MicroMark catalog. The red LED is just an example of what the output can be hooked up to. The real meat and potatoes are the two 'snorkles' sticking up. One's the sender and the other is the IR receiver. Wonder if they would work?

http://www.ares-server.com/Ares/Ares.asp?MerchantID=RET01229&Action=Catalog&Type=Product&ID=83232

And here an illustration of how it's supposed to work:

http://www.micromark.com/detailimgs/83232d.jpg


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## MaximuM (Jan 31, 2007)

Hello sed6, Yes Ive seen those before. Those mainly for trains but may work I suppose with the right interface. The 3mm Sensors are sold here and they are paired with the IR emitters. I am simply using the detector photoresistors. They seem to be more sesitive to regular light. Its not all quite together yet but the testing looks promising. Also the bright white LED's Im going to use are found here


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## 13013comstock (Nov 25, 2006)

I finally assembled a track last weekend with the SI set. After successfully bench testing my home-made IR lap timing setup, I thought I would have a winner. After it was installed on the track, only one lane worked, two others didn't, and the fouth counted randomly without being triggered. I did experience some random counts on the bench test, I believe from stress on the IR receiver. So I've decided I'm done with the photo method for lap timing; I've ordered some reed switches and will try those. (I'll keep the pedestrian bridge because it looks great.) Another funny thing about the lane that worked: the LapTimer2000 software seemed to be a lap behind with the timing, i.e. it didn't report the lap just completed, but the one before that. Is it the way I have the software configured or is it the way I started the session (photo receiver blocked or not blocked)?


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## Scafremon (Dec 11, 2006)

Craig Jorgensen said:


> The problem is that Radio Shack stuff is junk. So's that cordless soldering iron, which I'm sure you found out by now!


Every time I go to solder something I ALWAYS grab the Radio Shack Cold Heat Soldering Iron.

I fart around with it, trying to get it to actually solder.

Once I am completly frustrated with the Cold Heat piece of @#$%, my other iron is warmed up and ready to use.


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## Scafremon (Dec 11, 2006)

13013comstock said:


> So I've decided I'm done with the photo method for lap timing; I've ordered some reed switches and will try those.


That's what I ended up doing also.



13013comstock said:


> Another funny thing about the lane that worked: the LapTimer2000 software seemed to be a lap behind with the timing, i.e. it didn't report the lap just completed, but the one before that.


I think you might be referring to the very first pass, which starts the timer, and therefore doesn't register a lap. Basically, LT2000 starts each lane at -1.


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## 13013comstock (Nov 25, 2006)

Scafremon, maybe we're talking about the same thing, but here's what I observed. I would run a few laps and then purposely run a slow one. The slow lap would not be reported immediately after I crossed the line to end the lap, but when the next lap (which was again a fast one) was completed. I'm not explaining myself very well, but has anyone else seen this?


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## Scafremon (Dec 11, 2006)

Comstock,

We are talking about different things, but I also experienced what you described. I messed around withe the few settings available in LT2000, and was able to fix it. Try changing the Timer Resolution to 1ms. Since I was using what I thought was an older/slower computer, I initially set it at 10ms. Changing to 1ms was what I think fixed the real weird lap times I was getting. In my case, I was just pushing a car over my lap timing track, and sometimes it would register, sometimes it would not, sometimes it would give me a like a 35 second lap time, when I know it was just 4 or 5 seconds.

A couple other settings I use (which I am not sure why, but work) are I have selected the "Invert Lap Switching Logic", and I also have checked the "TrakMate compatable" setting, even though I am not using Trakmate. I think this setting may be required if you wire to pins 10-13 for your lanes as I did.

Hope this helps.


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## Slott V (Feb 3, 2005)

Scafremon said:


> Comstock,
> ...A couple other settings I use (which I am not sure why, but work) are I have selected the "Invert Lap Switching Logic".
> 
> Hope this helps.


This is most likely the solution to the problem Comstock described about the delayed lap counting. Most likely the software is registering the wrong part of the signal, i.e.; the amount of time the sensor sees light instead of the amount of time the sensor sees "dark". I dont' know why that option was written into the software as the wrong way is not applicable with a light sensor. Must be common logic with a "flip" switch for either reeds or LED sensor. Reeds and dead sections only need to interrupt the signal where LED sensor timing actually measures the amount of time the light stops entering the sensor.

A note on LED sensors: In most cases, normal room lighting is NOT enough. Especially flourescent light. You need a desk lamp or other incandescent light source positioned above your sensors within a foot distance MAX. Also make sure your sensors are at the surface of the track and are clean and scratch free or you'll get shadows. I built a sensor plug from Greg's site and installed the LT2000 software on a friends track and got it to work nearly flawlessly so follow instructions and part numbers carefully!  

Scott


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