Reposting here:
I have a grade crossing signal board that I have six IR detectors wired to (signals protect three tracks, so three IR emitters/detectors on each side of the crossing, one per track.) All the IR pairs are the type that are in a little black plastic brick, side by side, with a small plastic divider between emitter and detector.
I have the IR bricks between the rails, but the sensitivity is disappointing. If I put a small piece of white tape on rolling stock bottom, they work fine (I know black absorbs more IR energy, so the white tape reflects better). Before going the tape route for hundreds of pieces of rolling stock, is there a way to boost the sensitivity? This board does not have a separate adjustor for it, so it would have to be something else.
Thanks - I'm learning electronics as I go, so all help appreciated.
Todd
Hi, Todd
I use IR detector/emitter pairs from the kits included with LogicRail Signal Simulators and the Grade Crossing Pro boards. They mount one (HO) tie apart and are angled toward each other at about 10°.
These seem to function pretty well althouth there is a sensitivity pot on each board. Maybe the problem you're having is related to the IR bits being housed in the same cube.
Perhaps try to find separate emitter/detectors and mount them a little distance apart, aimed toward a central point about where your car floors bisect the beam?
Good Luck, Ed
*I was typing more but when I hit "save changes" I got kicked out then found out the thread had been locked
Toward the end of this document there are some pointers regarding the use of IR detectors.
http://www.logicrailtech.com/od-1-ir_inst.pdf
Hi Todd,
I know the detectors you're talking about because I tried them too and had the same problem.
I switched to using a single LTR301 phototransistor instead of the emitter-detector pair. I found it works much better. The LTR301 is much smaller (it's about 1.5mm thick) so it can slide underneath the track with its little detector spot between ties. It's small enough that you don't even need to plan for its placement; I use foam roadbed and can just slide one in anywhere.
I don't need any IR emitters with it. I pull its collector up to 5V via a 100k ish resistor. When there is no train on it, ambient light activates it, and the collector is pulled down to ground. When there is a train sitting on top of it, ambient light is blocked enough that the collector remains pulled high. I find it much easier than the detector-emitter pair, and no taping/painting of rolling stock is required.
Datasheet: https://www.sparkfun.com/datasheets/Components/LTR-301.pdf
It's called a infrared phototransistor but I've found it seems to work fine with whatever ambient light is bouncing around my room. I don't even use incandescent lights.
There's not much you can do but try different sensors with different characteristics. Adjusting the position of the ones you have might help.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
BigCityFreightI have the IR bricks between the rails, ... is there a way to boost the sensitivity?
are they angled such that their lines intersect at the height of the bottom of the car?
have you maxed the current to the emitter and maxed the resistance on the detector?
low level TTL is fairly low (~0.8V), arduino atmel 328P is ~0.3V. you could try a 555 which is 1/3 VCC, ~1.7V at 5V.
greg - Philadelphia & Reading / Reading
Thanks -- I'll try these out. Does it matter which side the resistor is on?
BigCityFreightDoes it matter which side the resistor is on?
no
what are you connecting the detector to?
BigCityFreightAll the IR pairs are the type that are in a little black plastic brick, side by side, with a small plastic divider between emitter and detector.
i assumed you have a emitter/detector pair similar to (b) in the lefthand image below. there are 2 wires on either side, one pair for the emitter and the other for the detector which are presumably connected to some circuit similar to the one below.
R1 can be made small to maximize the current thru the emiter for a know supply voltage. R2 is made large so that even when a limited detection occurs it creates a large change in voltage across the resistor.
i the circuit below, i'm not sure why they have a transistor. The transistor requires ~0.7V to start conducting and R4 raises that voltage as soon as it does.
gregc the circuit below, i'm not sure why they have a transistor. The transistor requires ~0.7V to start conducting and R4 raises that voltage as soon as it does.
the circuit below, i'm not sure why they have a transistor. The transistor requires ~0.7V to start conducting and R4 raises that voltage as soon as it does.
If the voltages called out on the circuit are to be beleived, the .86 volts at the R2/R3 junction is just slightly above the maximum 'low' voltage for the 74HCT14 inverter. So it would appear to be acting as just a level converter. A different sensor, with a different IR phototransitor, could probably make that unecessary.
gregc I have the Vishay tcrt5000. Datasheet here: https://www.vishay.com/docs/83760/tcrt5000.pdf What kind of resistors would I need to maximize the sensitivity? I'm struggling to understand much of this. BigCityFreight All the IR pairs are the type that are in a little black plastic brick, side by side, with a small plastic divider between emitter and detector. i assumed you have a emitter/detector pair similar to (b) in the lefthand image below. there are 2 wires on either side, one pair for the emitter and the other for the detector which are presumably connected to some circuit similar to the one below. R1 can be made small to maximize the current thru the emiter for a know supply voltage. R2 is made large so that even when a limited detection occurs it creates a large change in voltage across the resistor. i the circuit below, i'm not sure why they have a transistor. The transistor requires ~0.7V to start conducting and R4 raises that voltage as soon as it does.
BigCityFreight All the IR pairs are the type that are in a little black plastic brick, side by side, with a small plastic divider between emitter and detector.
rrinkerSo it would appear to be acting as just a level converter.
fig 5.4.2 on that page shows a slotted opto being tested which doesn't require much sensitivity. I think reflected sensitivity may require a different type of circuit.
BigCityFreightWhat kind of resistors would I need to maximize the sensitivity? I'm struggling to understand much of this.
but it's still not clear how you're using the opto, what are you connecting it to?
and is the detector subject to ambient incandescent lamps/sunlight in the room
BigCityFreight What kind of resistors would I need to maximize the sensitivity? I'm struggling to understand much of this.
according to your datasheet, the Forward current (emitter) is 60ma. under Basic Characteristics, the Forward voltage (drop) is 1.5V. With 5V supply, a 59 Ohm ((5 - 1.5) / 0.06) resistor results in 60ma. (something more to be on safe side.
It's connected to a cheap ebay board that controls a grade crossing signal.
BigCityFreightt's connected to a cheap ebay board that controls a grade crossing signal.
can you post a link from ebay?
Here you go.
https://www.ebay.com/itm/1-set-grade-crossing-signal-automatic-control-system-with-sound-effect-blink/401721782487?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
i was expecting to see a part no. that I could look up to see a schematic for what the opto is connected to. Based on your questions, it seems unlikely that you'd modify the circuit.
so at this point, the only thing i can suggest is the alignment of the detectors which also doesn't seem likley without modifying the housing.
there is of course that pot on the board the opto connects to. is it for adjusting the sensitivity?
The pot is labeled as "speed" and I think somewhere on ebay description it says it's for the flash rate, though the flashing board (yellow one) has its own adjustment pot. I will try the one on the green board and see what happens.
The sensors come out of the brick pretty easily and I already have an oversized hole cut, so I will try angling them. I also have the optical sensors on order that another poster suggested to swap in as a backup plan.
If all else fails, I have plenty of white tape to put on the bottom of rolling stock.
I appreciate everyone's efforts here. I'm learning a lot.
Thanks!