my AS level engineering project...

[soho07]

hi everyone. basically i'm taking this AS level in engineering and we have to deisng and make something with a function that will help people in everyday life etc etc that hasn't already been done or is a significant adaption of something that has been done.
i've been given this idea by a signal engineer to do a detection circuit for level crossings to detect anyone that gets trapped inside. i'm thinking of using PIR emittors and sensors for this and i'm only making a small model out of MDF or similar (this will be like a rectangular cuboid shape except with 2 sides instead of 4 but obviously still with a top and bottom, and the circuit will go between the top and bottom and i'll just draw a traintrack on the top part)

basically there are two outcomes which are represented by two sets of lights. the first is for the operator of that level crossing and that will consist of a green LED for 'crossing clear' and red for 'crossing obstructed'
the second is for the train driver, red so the driver knows to start braking the train, yellow to say 'crossing clear but proceed with caution' and green for just 'carry on as normal'

i'd like to put a scan of this flowchart i made pointing out the whole system but for some reason i can't paste images in here and i have to type a URL in?
anywho, basically first the sensors are activated.

if they detect something - 'crossing obstructed' light is lit and so is the RED light for the train driver
if not - GREEN light (or crossing clear for operator) for both operator and train driver

sensors are activated again

if the detect something 1st AND 2nd time (or just 2nd time)- 'crossing obstructed' for operator and RED for train driver
if they detected something 1st time but NOT 2nd time - 'crossing clear' for operator, YELLOW for train driver (approach with caution)
if nothing both times - remains GREEN for both

this is obviously much better illustrated with a flow chart, but i hope you all understood this! of course don't hesitate to ask questions (provided i can answer them!)

the trouble is i'm not very familiar at all with circuits and so i don't know how to go about constructing one for this, or what components to use, or even how to read other circuits (ie look at one and actually know what it does) so can anyone help me to tell me what i need or what the kind of circuit i'm trying to make will look like?
i'm afraid if anyone can help they'll need to explain in really simple terms because otherwise i really won't understand!

hope it wasn't too long a read....thanks if you can help!

P.S. i'm new here so sorry if i've somehow done something wrong because i know some forums have different rules etc.

 

[soho07]

can anyone help me on this please?

 

[Darth Bagel]

I'm assuming that the area we're looking for a trapped person within is some reasonable boundary around a railroad crossing?

For a real version of this I'd probably use something like an ultrasonic rangefinder, I haven't had good luck with IR trying to cover large areas. You can use a smallish PIC to read the sensor and handle the lights.

And you can include the flowchart as an attachment (look towards the bottom of the reply screen).

 

[soho07]

thanks for the tip, but i edited it with paint because i scanned it from handwriting and thought it looked too scruffy to read, but it won't accept paint images and i tried putting it in a word document but it turns out it exceeds the space allowed anyway!
very fustrating...

anywho, it's detecting people trapped within the area of a level crossing when the barriers are lowered, so between the barriers really in a rectangle shape
i originally wanted to use ultrasonic but i was advised to use PIR because they're more accurate/sensitive and cheaper. i'm only using a small model too so i won't need a huge range of detection

more ideas welcome!

 

[JimB]

The major difficulty with this project is finding a device which will detect the presence of a person or vehicle within an open area.

One possible way would be to have a series of light or IR emitters on one barrier and light or IR detectors on the other barrier.
If one or more of the light/IR beams is obstructed, then there is something on the crossing.

I could think of several reasons why this scheme would have problems in the real world, but it could make a good starting point for a school project.

JimB

 

[soho07]

yes i see what you mean like small animals or leaves blowing disrupting the beam etc but i am going to set it (somehow) so that it only works when two or more are triggered off at the same time to stop this

also my teacher said that leaves etc don't give off body heat and so won't be detected by the infrared possibly. and to avoid detecting cats/dogs etc they could simply be placed (theoretically, as i'm only making a model) at a high enough height

the things, how would i even start constructing a circuit with all these functions? i don't really know how to make it. apart from the obvious components like LEDs, emitters and sensors, what other components and how many of these components will i need?

any links or pictures of suitable circuits would be great, obviously if they need adapting to suit my project that's fine also

 

[Bfish2007]

I kinda know what your talking about here, cause i am in Electrical engineering at one of the PSU campuses. I also did some things like this when i was younger. We are working with the basic stamp, but with that there is alot of progamming behind it. With this are you trying to have like a motion sensor added on to it with the LED lights?

 

[Torben]

also my teacher said that leaves etc don't give off body heat and so won't be detected by the infrared possibly. and to avoid detecting cats/dogs etc they could simply be placed (theoretically, as i'm only making a model) at a high enough height

Just wondering--if the sensors are high enough to miss, say, a German Shepherd, wouldn't they also miss the average 2-year-old child? Or has the instructor said that this isn't an issue for this assignment?


Torben

 

[audioguru]

Have you ever seen a fully loaded 80mph freight train stop? It takes miles and miles and many minutes. Screech, Wham. Whoever was in the way is gone.

Concentrate on warning pedestrians and car drivers that a train is coming. Then they can move out of the way. Or sweep them out of the way.

 

[BigAdv]

have a look at the elevator doors the next time your in a building. chances are that it has a ir detector, not a new idea, but could be used to do what you are asking.

 

[soho07]

i'm not actually incooporating into the circuit a way for the train to stop. that's not my problem or relevant to what i'm trying to do. otherwise there'd be endless issues and problems leading to even more problems etc etc

the only thing i'm really trying to do here is to make a working PIR emitting and sensing/recieving circuit to theoretically detect anyone trapped between the barriers of a level crossing, and when two or more IR beams break that would trigger off the lighting of the LEDs (supposedly for the operator and train driver to see). that is really all. it's what i've been assigned to do so it's not really my idea if any of you think this sounds sketchy or that is needs changing etc

so basically all i want to know is what would i need (apart from the obvious components such as the LEDs themselves and the emitter and recievers) and what would the circuit be or look like?
by the way i'm going to use two emitters and receivers (i originally planned to have 4 but they're quite expensive and i'd only need two anyway just to say it works, because it kind of needs both beams to be broken in order to work) i'm confused about things like where to place the components, in what order (i don't mean which one first etc, but again where to place them), resistors and how of those i need or how many ohms etc and other components that might be necessary for this

about the dog/child thing, as i said i'm only making a small model so this would need to be carried out, i won't actually have to place them at a certain height. however i will have to change them somehow so they're not sensitive to detecting small things like leaves blowing or insects etc because obviously this would be very disruptive when i'm trying to test and evaluate it!anywho, it was a good question and thanks for asking!

P.S. is there some kind of software that allows me to construct circuits somehow and print them off? or can anyone recommend a suitable circuit to me?

 

[audioguru]

The train takes up to 2 minutes to stop. A person is detected and your circuit lights the LEDs to warn the train driver to stop the train. By the time the train is stopped then the person has gone away.

You need to warn the person, not the train driver.

 

[Darth Bagel]

i'm not actually incooporating into the circuit a way for the train to stop. that's not my problem or relevant to what i'm trying to do. otherwise there'd be endless issues and problems leading to even more problems etc etc

the only thing i'm really trying to do here is to make a working PIR emitting and sensing/recieving circuit to theoretically detect anyone trapped between the barriers of a level crossing, and when two or more IR beams break that would trigger off the lighting of the LEDs (supposedly for the operator and train driver to see). that is really all. it's what i've been assigned to do so it's not really my idea if any of you think this sounds sketchy or that is needs changing etc

so basically all i want to know is what would i need (apart from the obvious components such as the LEDs themselves and the emitter and recievers) and what would the circuit be or look like?
by the way i'm going to use two emitters and receivers (i originally planned to have 4 but they're quite expensive and i'd only need two anyway just to say it works, because it kind of needs both beams to be broken in order to work) i'm confused about things like where to place the components, in what order (i don't mean which one first etc, but again where to place them), resistors and how of those i need or how many ohms etc and other components that might be necessary for this

about the dog/child thing, as i said i'm only making a small model so this would need to be carried out, i won't actually have to place them at a certain height. however i will have to change them somehow so they're not sensitive to detecting small things like leaves blowing or insects etc because obviously this would be very disruptive when i'm trying to test and evaluate it!anywho, it was a good question and thanks for asking!

P.S. is there some kind of software that allows me to construct circuits somehow and print them off? or can anyone recommend a suitable circuit to me?

Based on my understanding, PIR is different from IR beam-break detectors. Which do you plan on using? Also, again from my experience/understanding, your professor(s) will want you to include in whatever report at least a brief mention of how your design will scale to the real world.

Also, do you intend to put bugs and leaves in your model? I'm a bit confused about why you'd need to make adjustments for them.

The train takes up to 2 minutes to stop. A person is detected and your circuit lights the LEDs to warn the train driver to stop the train. By the time the train is stopped then the person has gone away.

You need to warn the person, not the train driver.

Depending on what kind of sensors he uses, it could just be detecting *objects* on the crossing, which could include things like debris and disabled vehicles.

 

[soho07]

firstly, i'm a she.

with my original idea, i was planning to optionally have some kind of voice recording or similar to warn someone off the track, or having two more sets of barriers so that the inner barriers would be raised and the person walk through and then the barriers lowered again etc so they stay within the inner and outer barriers

but the person who assigned this to me said i shouldn't worry about those things, because it would distract me from what i was trying to do, which is construct this circuit.

if i had time and knew how to, i would incoorporate this voice recording but i can't even start on how to do the actual circuit with the main function, so until i can get the main part done, i can't do those extra things.

i will discuss with my teacher about the red LED idea, not that i could do much more to change it because it's not as if i'm going to design a braking system etc for the train. although, like i said, if i have enough time i could incoorporate the voice recording.

no i will not use bugs etc for the circuit, i'm just going to make sure small things won't disturb/break the beam or be detected etc. remember this is REALLY small scale so if i used a leaf i might as well use my hand or finger etc but i suppose i could use another object just to test that it doesn't detect objects without heat.

by the way this AS level that me and my classmates are doing was offered to us 2 years early, so i'm still doing GCSEs and kind of juggling 10 GCSEs with an AS level, so hopefully that explains my inexperienced...ness and slight incompetency! so sorry for having to get anyone to explain things really simplistically

 

[soho07]

oh also, about the report, yes i will mention this in my coursework about how it would work in real life. but i will explain, as i have done, that i will not be carrying this out in real life.

can anyone please suggest ideas for circuits?

 

[KMoffett]

soho07,

All of your logic functions can be handled by a small, cheap micro controller as someone mentioned. Since speed isn't a critical issue from your description, I'm going to suggest a PICAXE. **broken link removed** These are cheap, easy to program in BASIC, need minimum hardware, and have an active support Forum. I'm sure others will suggest their own favorite uC's...with supporting rational.

I'll go along with Darth Bagel for IR emitters and detectors. I did this a while back to detect the daily activity level of 3mm-5mm long, blind cave fish in a 1cm x 1cm x 9cm plastic tank. With a little creativity, this could be scaled up to your model size, or with enough money and added complexity, to a full scale model. For starters Google: IR detector circuit. Lots of hits on real basic stuff.

Keep to your instructor's definition for the project...You can "what if" yourself to death. (and boy can we help you there! ) Save these for "other considerations" in your summary.

Ken

 

[soho07]

thanks kmoffett, i didn't want to get too sidetracked!

both my teacher and the guest engineer told me to use this circuit (the one attached) but to replace the phototransistor with a PIR reciever/sensor i think and the LED will stay the same as the output

this is only for now though, but we'll keep adapting this in the coming weeks (after my good old mocks before and after christmas!)

thanks for the help so far though! i'll keep posting if i need anymore help. feel free to comment on the attached circuit though

 

[audioguru]

Hi Mademoiselle (or girlie),
The comparator oscillates if the input reaches the threshold slowly.
The datasheet and everybody recommend adding a little positive feedback to create a small hysteresis. Then its output will switch quickly and not have time to oscillate.