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Feedback on 555 timer Schmidt Trigger design

colporteur

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Can I get members insight into using a 555 timer as a schmidt-trigger design that I pulled from the Internet?

I found this schmidt-trigger design using a 555 timer. I would like to use it to condition the output of a photo-resistor. The 555 timer output will feed the input to a Arduino Mega. I'm in the process of bench testing the setup to finalize component values. While testing I figured I would throw it out to some more enlightened minds than mine for feedback.

I'm using the 555 only because I have a stock of them. I don't have any readily available smidth-trigger IC's so I figured I would go with what I have and build from scratch. Building from scratch especially using Internet designs comes with risk. I was hoping to mitigate the risk by getting community feedback.

If inquiring minds suggest you don't want to do this, that is a good thing.

  • 0 in reply to colporteur

    Maybe you can simply use ambient lighting as the light source for your photo sensors. A little opaque tube facing up would allow ambient light to reach the sensor only when a car is not above the sensor. It should be workable over a wide range of ambient lighting, If not you can set the sensitivity to be high and almost completely block all light with a simple tab under the truck.

    Another idea is to use a gap style optocoupler where a little wing under the train would pass through the gap and interrupt the optocoupler. (no signal conditioning required) 

  • 0 in reply to AE7HD

    image

    Is this the sensor placement you are suggesting?

  • 0 in reply to dougw
    dougw said:
    a gap style optocoupler where a little wing under the train would pass through the gap and interrupt the optocoupler

    You could perhaps use the wheel of the train for that to avoid modifying all the rolling stock but you would likely only get pulses as the train passed - no way of detecting if a train was sitting there unless it had stopped with a wheel in the sensor. 

    Lift the beam up higher and then the train could break a wider beam but you would need appropriate track-side scenery to disguise the emitter/detector or light pipe. 

  • 0 in reply to Jan Cumps

    I din't have any success using a rectifier. That may have had more to do with me than the rectifier. I was getting tired of crawling underneath the bench towards the end of the project.

  • 0 in reply to Jan Cumps

    Sorry JC I have a reluctance to invest anymore effort in the IR solution.

    Modification of the train cars is something that frowned upon. This applied to even putting a magnet for another solution. I can place things of the cars of our layout but met opposition on other layouts. The fixing of the mirror will hold some challenges. The under carriage of cars is not consistent. The mirror would only sense one place. This is the same issue I had with the hall-effect sensor. The car can coast of the sensor.

    Thanks for the suggestion just the same. I will keep the mirror solution in my back pocket. Maybe I can use it at some point.

  • 0 in reply to colporteur

    A few years ago I did something similar with reed switches, something very simple.

    (+) VenTTracker #06 -  Window Sensor Prototype - element14 Community

  • 0 in reply to javagoza

    Nice design and layout. What is the sensor the magnet on the upper small square block triggering. A read switch?

  • 0 in reply to colporteur

    The sensor in action. Impressive Smiley

  • 0 in reply to colporteur

    That should work. Remember, though, don't ground it to the track. The 555 circuit can sit right under the copper pieces, so there is very little wire to add parasitic capacitance.