Thanks GMPULLMAN for referencing our GCP and instructions.
Most photocells which I'm familiar with, such as those we use, have a lower resistance when light hits them and a higher resistance when light is blocked. So, depending on the way the detection circuit works the photocell wiring really matters! For our circuits we want to know when the light is blocked from the photocell (i.e. a higher resistance). As such you MUST wire the photocells in series. As others have noted, a photocell is a light-sensitive resistor. With resistors in series the effective/overall resistance is additive. When either photocell in a series is blocked from light its resistance goes up and thus the overall resistance goes up! That's the condition we're looking for. Wiring them in parallel would have some unsual results (look up the formula for calculating resistance in a parallel scheme!). For what it's worth, our circuits all have a trim pot for adjusting the sensitivity to overhead light. This also helps compensate for the increased resistance of photocells in series.
Hope this wasn't too techie! It's what you get when an electrical engineer responds!
RR_MelThat’s correct . . . but I don’t know if you can parallel three sensors to one detector.
I don't know how close the Circuitron arrangement is to the Grade Crossing Pro from Logicrail, which is what I am using.
In either case, the GCP instructions have a bit of discussion about using multiple photocells with one detector. And an example of series-parallel wiring of the photocells.
https://www.logicrailtech.com/gcp_inst.pdf
Scroll down to page 5.
In my case I used two GCP units to protect each track.
Good Luck, Ed
Would something like this work for putting the sensors in parallel? Each different wire type is in a different color.
FRRYKid RR_Mel Mine are paralleled. In series all tracks would have to be occupied, paralleled any track occupied triggers the crossing. Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps. I not visualizing a parallel circuit very well for some reason. Could you post a diagram for me. (Parallel circuits have always caused me visualization problems anyway.)
RR_Mel Mine are paralleled. In series all tracks would have to be occupied, paralleled any track occupied triggers the crossing. Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.
I not visualizing a parallel circuit very well for some reason. Could you post a diagram for me. (Parallel circuits have always caused me visualization problems anyway.)
the DT-2 instructions aren[t very specific about what they mean by opto sensor. the image below is for Circuitron 800-9206 Opto-Sensors. They look like CDS cells. Since they are often used in a resistor divider circuit, not sure how that can be used in series, parallel or in multiple circuits with the DT-2
greg - Philadelphia & Reading / Reading
There are two kinds of photo cells as well - some have high resistance when dark, and others have high resistance when light is on them. Depending on the circuit, parallel may or may not work. Worth trying.
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
most IR sensors are just optical transistors that conduct when a sufficient amount of light hits them, pulling a circuit to ground when detecting light or allowing a circuit to be pulled high when light is blocked from reaching them.
depending on how they are driven, a single sensor could drive multiple detection circuits
do you want to have multiple DT-2 units (adding links would be helpful) triggered by a single sensor?
No. The opto-sensors are basically a variable resistance based on the amount of light it receives. The circuit is designed to be turned on with X resistance and off with Y resistance.
By putting them in series, the total resistance when light hits them will be higher, but still keeps the circuit off. However, when only one is covered, the resistance change isn't sufficient to turn the circuit on due to the other three still providing a high resistance.
At least that was MY experience. If someone does have a simple answer, I'd like to know as well as I have a similar situation and didn't want four separate circuits if at all possible either.
Got yet another one for my Forum friends: Can a modeler put Opto-Sensors in series if the crossing is covering multiple tracks with a DT-2 unit? (e.g. A1, A2, A3, B1, B2, B3, C1, C2, C3, D1, D2, D3.) I have a spot on my railyard where it is covering three tracks. I know prototypes have multiple track crossings but I want to make sure that I am connecting things right. As usual, thank you for any assistance that can be provided.