Feedback on 555 timer Schmidt Trigger design

Awesome feedback folks. Sorry for not responding. The regional telco decided to take my money and not provide me internet. Just got it fixed today. I was beginning to twitch and go to the library for a fix.

I have a fair amount of experience with 555 timers, IR sensing, break beam circuits, etc. I'd like to help. But I need to know what you are trying to do. What is the ultimate goal?

Hopefully Sean can confirm, and it may need a photo of the current setup, but I believe it's related to model train detection.

There's a thread here that came before this one:

 IR sensor: all that glitters is not gold 

I think the current thread is to do with trying a different method with what Sean currently has, to save time ordering things.

Hi colporteur ,

Could you please show a detailed photo of the setup that fails, so that it can be easily seen what sort of distances and objects are involved?

There four sensors. Two senors paired at the front of the train and two paired at the rear of the train.  On initial startup all sensor must read the car and then after that they are OR'd. The sensor pair spacing accounts for the gap between cars. Since locomotives don't stop abruptly, the coasting is taking care of by the pairing.

Issues:

IR noise from LED over head lights in the room, Halogen trouble light under the bench and sun from a large window impact the sensitivity of the sensor. When sensitivity set high lots of false positives. When sensitivity set low, failure to detect car.

Physical attributes of the bottom of cars and locomotives not consistent. Highs, lows and voids impact the sensor getting a reading. This makes it difficult to pass the initial all sensor reading check before starting the train motion sequence. Moving the train mm might light one sensor and turn off another.

The IR sensors are impacted by the IR noise. Reduce the sensor sensitivity to limit the noise and the sensor doesn't read. Circle of life I don't want to die on any more.

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RE: Feedback on 555 timer Schmidt Trigger design

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There four sensors. Two senors paired at the front of the train and two paired at the rear of the train.  On initial startup all sensor must read the car and then after that they are OR'd. The sensor pair spacing accounts for the gap between cars. Since locomotives don't stop abruptly, the coasting is taking care of by the pairing.

Issues:

IR noise from LED over head lights in the room, Halogen trouble light under the bench and sun from a large window impact the sensitivity of the sensor. When sensitivity set high lots of false positives. When sensitivity set low, failure to detect car.

Physical attributes of the bottom of cars and locomotives not consistent. Highs, lows and voids impact the sensor getting a reading. This makes it difficult to pass the initial all sensor reading check before starting the train motion sequence. Moving the train mm might light one sensor and turn off another.

The IR sensors are impacted by the IR noise. Reduce the sensor sensitivity to limit the noise and the sensor doesn't read. Circle of life I don't want to die on any more.

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glue little mirrors (like those on Indian elephant souvenirs) under the cars. 

I have two locomotive assigned to two trains for the development environment. Easy to place magnets front and back or mirrors. In production there are over ten locomotives and a few hundred cars. Train car can be any kind. The magnet is not scalable in my production implementation.

I used the mirror approach for a turntable speed detector:

 Vintage Turntable repair: Can I fix a Perpetuum Ebner from 1958 - part 7 - Make Speed Sensor from Scrap Parts 

With one of the mirrors that dropped of this kind of elephant :) 

1 tiny animal has enough mirrors for the whole wagon park. If you combine that with the modulation suggestion, I bet you have a winning combination.

If the room is well lit, perhaps sense for ambient light using a light detector with a snoot around it. The absence of light falling on the sensor from above means something is directly overhead blocking the light and probably a train.

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) 

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. 

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.