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Photocells Used in the AutoWorld Dragstrip Set?

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  • Photocells Used in the AutoWorld Dragstrip Set?


    Does anyone have any information as to the brand or spec of the sensors used in the AutoWorld Dragstrip set? I currently use reed switches for lap counting as I am not too keen about the aesthetics of using light / infrared bridges and such, and was wondering whether these photocells or something similar might be useable instead. The sensors seem to work well under normal ambient light conditions.

    Sorry if the question has been asked elsewhere before, but any thoughts or insights are much appreciated!


  • #2
    You can in fact use these photocells for lap timing and they are available any electronics or Radio Shack store. Greg Braun has a nice diagram of how they are assembled if you want to get a better idea: I have used this system for over 5 years now and I haven't had a sensor go wrong yet! PM me if you have further questions!!


    • #3
      I have built lap timers and drag sensors using the Radio Shack 1/4 inch photo-sensors. They work very well, but you will have a much better experience and consistent response using a light bridge/source closer to the sensors. I purchased a battery powered LED light from Wal-Mart for $5. The light uses very little power, so the batteries last quite a while. The housing is fairly small fitting under a walkway bridge, has 3 strong LED lights and lights up the sensor area very well. I used the Slot Race Manager product with no problems.



      • #4
        pshoe64, do you have any pics of the light bridge? Just looking to get some ideas.


        • #5
          SlottoFill, I'm happy to share my HO scale light bridge adventures for ideas. Pretty sure it'll make RonDo, the OP, even more hesitant about the aesthetics of light bridges, though!

          Maybe someone with a more polished light bridge example will post after me to set things right aesthetically?


          • #6
            Tripping the (IR) lights fantastic...

            What? Laptimer 2000 is free??? Well, I had to try that out right away. [EDIT: I wish RC was around last year when I originally wrote this up. Nowadays I think I would've started out with Race Coordinator software. This rig will support RC, of course, so when I get time, the switchover should be straightforward.]

            The Shack had the IR LEDs in stock, but was out of IR phototransistors and out of matched pairs. I think going with the matched pairs is good advice. But I can find my way around a datasheet so I stopped by the local dusty old electronics store and picked up four of their flavor of IR phototransistors with peak sensitivity of 940nm to matching the Shack’s LEDs peak output.

            I wired the photosensors into a parallel printer cable and I popped the photosensors in a piece of track. I chose a place in the track that could accommodate a timing gantry and where cars were not likely to crash or slide across lanes.

            I did all my testing with a strong droplight over the sensors because I wanted to ensure I had the system working without introducing any mismatched sensor/LED issues into the equation. After not too much tweaking it worked fine with the droplight.

            Not so much with the LEDs, unless they were a little closer than I liked to the sensors. So I doubled down on the LEDs, putting a pair above each lane’s sensor and that did the trick. More light and less alignment sensitivity of the gantry to the track – what’s not to like?

            Here’s my test-rig circuit board made out of luan, what else?

            As if we needed another reminder of why most engineers should leave the soldering to a good technician.

            The camera in my trusty iPhone (like most any modern cellphone) dips into the IR spectrum, so a photo showed the LEDs kicking out the photons well enough and even helped with aligning the test rig gantry correctly over the sensors.

            Here’s the temporary gantry – just some cardboard uprights to support the LEDs overhead.

            You can see both the LEDs (pointing down from the board above the track) and the sensors (peeping up from the track surface) if you squint.

            It works. I'm counting laps! Is this a great country or what??
            Last edited by Rolls; 03-04-2011, 12:36 AM.


            • #7
              An upgrade to the light bridge

              The gantry is in need of support that is not so woefully temporary. There's the test rig light bridge... It's kind of teetering all alone in the center of three 4-lane straights.

              I really like the position because it's accessible from the drivers' positions and it's a low-crash, no-slide area bcs cars are slowing down for the left-hander up to the top straight (and the criss crosses just before that).

              I mocked up a possible gantry support design in cardboard. It reaches from the inside straight waaay over to the center straight where the sensors be.

              Looked like it'd work so I cut two sides like this out of luan:

              And I got my other favorite building material out (Home Depot yardsticks - 3 ft of pretty good wood for 61 cents!) If you can put up with the orange print, they're as good as what they sell for $1 a foot in the molding aisle. Nicely marked for cutting, too.

              The circuit board will drop into this and sit at the lower level, supported by yardstick wood. The little cross-member with the orange letter "T" on it supports the middle of the LED board, so it aligns with the gap between each pair of lanes in the 4-lane straight below. The board sits way out at the end of the gantry, bcs it has to reach over one straight to get to that center straight.

              And a removeable top piece drops on, recessed by a half inch. It acts as a cover for the LEDs and a "floor" for spectators standing on top of the gantry looking out over the resulting half-wall.

              Power comes from a small wall-wart below the table and wires supplying about 30mA to the LED board run up through the base and will be covered by drop in stairs, or a very lame facsimile thereof.

              It's reasonably ventilated, but there's not much heat to build up with 12V at 30mA total (all 8 LEDs are in series).

              And it'll eventually be covered with sponsor logos or some other more polished signage. It's certainly an upgrade from the cardboard uprights that held the LED board 'til now. And it works!

              Here it sits in place of the cardboard uprights with some banners on copy paper tried on for size... just stuck on temporarily to see how different decos might work.

              And that's how we're counting laps for now. Hope it stimulates some ideas for others at this stage of their track building adventure.


              • #8
                Originally posted by RonDo View Post

                I currently use reed switches for lap counting
                Nice work, but still wondering why the change from reeds?


                • #9
                  Bananasmoothie wrote - 'Nice work, but still wondering why the change from reeds?'

                  I was just thinking theoretically. I would think that magnetic fields can vary between two cars, hence their triggering points with respect a reed switch (and thus where the actual timing event occurs on the track ) could be different. I trust the ones that I use { } and have never had a problem with missed counting. I would think that a light triggered device might be more precise. It would also take away variability introduced by magnetic fields - in a drag situation I can see how the AutoWorld photocell, DS Lapcounter infrared hardware. etc perhaps would be more precise. What would be really cool would be to use a group of them for multiple sector timing on a track {as I do with switches now} - thus my aversion to using bridges.

                  You guys know all this of course - and one late insomnia ridden night it all just popped into my brain and WOULDN'T LEAVE . I hope I made sense with what I wrote. In the real world the timing difference - I mean we are talking millimeters with cars moving at a high FPS - is probably not really worth the effort taken from my other totally irrelevant 'thought experiments'



                  • #10
                    That is a nice light bridge.


                    • #11
                      I went for the clear plastic option similar to this 1/32 version. I travel around with my tables and so far it's held up very well. RonDo aren't you glad you made the switch!!


                      • #12
                        Any of you guys have a circuit diagram for the light bridge including a parts list if possible?

                        The light bridge I built sits over the trakmate light bridge because I didn't want to mess with it, but seeing through the plastic it looks easy enough to build if I have the right parts and a diagram.


                        • #13
                          Originally posted by RonDo View Post
                          Bananasmoothie wrote - 'Nice work, but still wondering why the change from reeds?'

                          I was just thinking theoretically. I would think that magnetic fields can vary between two cars, hence their triggering points with respect a reed switch (and thus where the actual timing event occurs on the track ) could be different.
                          True, but the triggering point should be the same for each lap of the same car

                          I used optical on my drag strip btw, but mine are mounted as horizontal beams cos it's only 2 lanes and 90mm apart lol


                          • #14
                            Does anyone know if the starting line photo cells in the Autoworld drag strip only indicate a false start or do they actually trigger the countdown on the christmas tree as in real life?


                            • #15
                              What are the best rear tires for the Autoworld 4 Gear cars?