Crossing signal detection, photo cell questions

[Tylerf]

Hi
so I'm attempting to figure out how to fix my crossing signal system, it's been puzzling me for months now. So I've been told by the "experts" on this system that it's possibly the photocells being no good. I've tested all the cells for resistance and I've gotten readings from 6-19 and even a 0, and I'm not sure which readings, high or low, are good and which are bad? Anyone know more than me about photocells, please help...I may just have to switch to infrared sensors!

[richg]

The below site has all the info you need. Store his site in Favorites. You will probably use it a lot. Make sure you read his Caveat Lector link. He expects you to know something about electronics.

http://home.cogeco.ca/~rpaisley4/CircuitIndex.html#Signals

Then click on, Return to Main Page. Have fun.

I use his DCC Amp meter circuit for our club NCE Power Pro 5 amp system.

Rich

[richg]

A Google search for using photocells will get you a lot of links and explain it better than I can

You might also consider photo transistors. Essentially a photocell  or really a photo diode with gain.

A Google search for photo transistor will explain it.

The link I sent you uses the photo transistors.

That is how I learned to use these devices before the Internet by reading. On the job training I call it.
I also picked up a lot of info on these devices from MRR projects in Model Railroader magazine, a very slow version of communication before the Internet arrived. No instant gratification back then.

Rich

[Tylerf]

Thanks, that site is great! I'm using a $200 signal logic system so I must figure this out...however my only options with system are the photocells or IR...so the less troublesome IR should be what I replace them with, plus I can run it in the dark!

[Doneldon]

Tyler -

I think Hogtrainz (I'm not making this up) or Factory Direct Trains has train detectors on sale right now.
                                        --D

                                             

[richg]

I just happen tohave a Model Railroader magazine nearby with photocell projects.
Feb 1995, Electrnics Symposium.
Unfortunately, the Model Railroader magazine site does not have the back issue any more for that month according to their site.

Rich

[richg]

We have not heard anything from you but I will assume you are still around. Below is a link with many explanations of photocells in model railroad circuits.
Are the photo cell s from the same batch/order?

Photocells have different characteristics depending on the application.

http://tinyurl.com/2d6baew

Rich

[Tylerf]

Yup I'm still around, and yes they were all from the same pack of 10. Thanks for the sites guys!

[richg]

Hi
so I'm attempting to figure out how to fix my crossing signal system, it's been puzzling me for months now. So I've been told by the "experts" on this system that it's possibly the photocells being no good. I've tested all the cells for resistance and I've gotten readings from 6-19 and even a 0, and I'm not sure which readings, high or low, are good and which are bad? Anyone know more than me about photocells, please help...I may just have to switch to infrared sensors!

How about details of this $200 lsystem?
What are the photocell manufacturers part numbers?
Any specs on the pack the cells came in?
Resistance of ambient light, resistance for no light?
Type of light source, fluorescent, incandescent?

How do your resistance values compare to photocells resistance values in the links I sent?

Sometimes you have to play with the resistors to get the logic circuit to switch at the appropriate level. That is why some photocell circuits have a pot to adjust.

Right now I am just grasping at straws for this issue.

Rich

[Tylerf]

Well the system is by signal logics, and the photocells were in an unknown package but I believe they are also signal logic. With no light they have full resistance, and with my incandescant train room lights the readings were like previously said 0-19. It is a module though so lighting is always different where we take it, so I'll be swapping them with IR sensors to make this whole thing much easier and more practical.

[richg]

Ok, sounds like you have a plan.

Rich