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Arduino build with custom PCBs

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  • Arduino build with custom PCBs

    I built two lap counters based on the Arduino Mega 2560 for use with Race Coordinator. One of the issues I experienced with the first attempt was trying to keep the tiny pins in place against the weight of the wiring to the sensors, track call buttons, and LEDs.
    I designed and had some PCBs professionally made. They eliminated the strain on the pins by connecting the sensors, buttons, and LEDs with Ethernet cables. It was just a matter of soldering in the Ethernet jacks, resistors, and LEDs as needed.
    Two sets of start countdown LEDs and a Leading Lane display are housed in a custom building that spans the track and 'pit lane'.

  • #2
    Nice clean layout. I like the use of the CAT5 connectors.
    They allow for improvements or changes without the need to complete point to point re-wiring.


    Mike

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    • #3
      Do the relay modules switch lane power? On my track the modules (Phidget cards) control 40A 12VDC relays that power each lane. This way a short doesn't blow the relay module.

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      • #4
        Originally posted by Maddman View Post
        Do the relay modules switch lane power? On my track the modules (Phidget cards) control 40A 12VDC relays that power each lane. This way a short doesn't blow the relay module.
        The Arduino controls relays that control the power to each lane. So yes, the Arduino is not affected should there be a short. My driver stations are all fused anyway.

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        • #5
          Nice work!

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          • #6
            Here is the full lap counter layout. Cat 5 cables to the sensors, start lights, lead lane lights, and track call buttons. A DC-DC Buck Converter drops track voltage down to 4.5V for the LEDs on the driver stations, and the trackside red/green lights.

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            • #7
              I was never worried about the logic board. Personally I would be a bit concerned switching track power with your relay board. Despite the fuse at the drivers station a dead short would probably either damage or take out a relay. That would require that the entire board be replaced. It wouldn't be the first time that a switching device fails first to protect the fast acting fuse. Typically that type of relay board is used as an intermediate point to control automotive 40A relays. The larger relays can take the abuse without complaint.
              Last edited by Maddman; 10-14-2020, 11:14 AM.

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              • #8
                Originally posted by Maddman View Post
                I was never worried about the logic board. Personally I would be a bit concerned switching track power with your relay board. Despite the fuse at the drivers station a dead short would probably either damage or take out a relay. That would require that the entire board be replaced. It wouldn't be the first time that a switching device fails first to protect the fast acting fuse. Typically that type of relay board is used as an intermediate point to control automotive 40A relays. The larger relays can take the abuse without complaint.
                This is used on an HO track. Classes are restricted to 6 ohm armatures at 18 volts. A 40A relay would be overkill.

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                • #9
                  r51-1d40-24_p.jpg

                  I know its an HO track but my suggestion is not overkill. Over the years I have inspected many HO tracks. Most use a 40A 12DC automotive relay like the ones shown here. A few have used even larger switching devices. As part of the design process you need to consider what could happen. A set of ski shoe pickups can short a lane should a car spin off in a turn. A controller can be hooked up incorrectly. Something else can happen. I have seen it all during my career. Should any of these happen the entire output of the power supply could be passed through the relay. Are you sure it will take it before the fuse lets go. Fuses take time to react and open in the event of a fault. You can look up the fuses time current curve and see for yourself. With the larger relays you have confidence that the fuse will protect the relay. I would not make that assumption with your track.

                  Immediately after I finish wiring a track one of my tests is to deliberately short each lane to verify that the installed overcurrent protection works as designed. Modern DC power supplies have overcurrent protection that may react faster than the fuse. Sounds fine but it really isn't. You want the protective device closest to the fault to interrupt the fault. If the power supply folds back before the fuse melts it impacts all lanes.

                  I am just trying to help. The larger capacity relay also has less voltage drop across it. You want power to go to the car instead of heating up wires and relay contacts..
                  Last edited by Maddman; 10-14-2020, 02:45 PM.

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                  • #10
                    Current rating of the contacts on the relays is 10A. Inline fuse is 5A. Should one go bad, I can replace the entire four relay module for $6. Voltage drop across the contacts is minimal (I've checked it, just don't remember right off the top of my head.) I've used these relays for several years without issues, but I thank you for your input.

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                    • #11
                      "You can lead them to water, but you can't make them drink"

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                      • #12
                        Originally posted by jmacartney View Post
                        "You can lead them to water, but you can't make them drink"
                        Especially if they're not particularly in need of the water.

                        If I were running open Neo cars with 1.5 ohm armatures, yeah, I'd use a more heavy-duty relay. I'm not, because my old eyeballs can't even see those things on track, and if they could, my old reflexes couldn't keep up with them anyway.

                        Last edited by Copperhead Motorsports Park; 10-15-2020, 01:23 PM.

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                        • #13
                          Sometimes the horse doesn't know that its thirsty. The term overkill spoke volumes. Depending on the power supply output a five amp fuse will not protect a relay with a ten amp rating.. Most relays only list their AC contact rating. The DC rating will be lower. In addition listed DC contact ratings are for non-inductive loads. Inductive load ratings for the same relay can be as much as an order of magnitude lower. Last I heard DC motors are inductive.

                          But some want to cancel a race when somebody hooks up wrong and fries a relay. 99.994% of the tracks out there won't have that problem.
                          Last edited by Maddman; 10-16-2020, 12:49 PM.

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                          • #14
                            Well, call me reckless, then. I'm willing to gamble on a $6 relay board.
                            One that has lasted me about 4 years so far.
                            Again, I thank you for your input.

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                            • #15
                              Hopefully no hard feelings. I wish you well with the track and your plans for it. I just tend to go a bit more conservative with my wiring. That's just my 40 + years of engineering and slot racing lesson learned coming through.

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