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Using more than two sensors

Posted: Tue Aug 20, 2019 10:22 am
by caprisam
Hi all,

Has anyone had any luck using more than two track sensors with one power box? I tried (without really thinking about it) just using a headphone cable splitter, which had the effect of still only allowing one sensor to work, but - I suspect - damaging the sensor input on the controller by feeding back false signals (as it now has difficulty registering some sensor activations. It may have also damaged one of the sensors). I don't know why, I suspect that the signal from one sensor is interfering with the signal from another (leaving one switch constantly closed or giving it a mixed open/close signal?)

Does anyone know of a solution? I'm trying to wire four sensors into one controller to operate a layout with a balloon reverse loop at either end and a zig-zag in the middle, so we're looking at the sensors operating two one-direction sections and two straight direction change movements. I've attached a basic track diagram by way of explanation.

I'm currently having to run it off two controllers and essentially split the layout in two - which worked fine until I managed to potentially bork one of the sensor inputs on one of the controllers! It's also a mighty expensive solution to what could be a very simple problem to fix!



NB the points are all one-way, as you can see the zig-zag is only run through one-way and bypassed on the way back. It's my attempt at a narrow gauge industrial shunting layout!

Re: Using more than two sensors

Posted: Thu Aug 22, 2019 9:07 pm
by dkightley
I'm not sure what you're trying to do is possible without investing in something more than the stock parts. I see two showstopping issues

First of all, I don't think you understand exactly what each sensor consists of....and the sensor does not "send" a signal to the controller box. Each sensor consists basically of an infra-red transmitter and an infra-red optical a device that senses when light falls on it and changes it's electrical resistance from either high to low...or low to high, I'm not 100% sure which without pulling a sensor apart and looking at the components in it!

Connecting two sensors in parallel....which is what you're saying you have done....will probably result in no detection whatsoever, as you will have reduced the resistance seen by the detection circuit in the controller....with it always being low! Either that, or only one will work - some of the time!

Secondly, having a "balloon loop" introduces a very real danger of shorting out the output of the controller....and causing terminal damage!! To get this arrangement to work safely, the track in the loop needs to be electrically isolated from both ends of the points....and the power connection switched in conjunction with the point...or at least the direction in which the point is being used! If you want this switching to take place with the train running, the power swapping will need to accompanied by reversing the direction of travel AT THE SAME TIME as the power connections are swapped in the loop....this will result in the train running into the loop, and then out again (now running in reverse).

Bottom line....this is not a simple layout to wire up for controlling trains. Far from it, it needs some electronics knowledge to solve! Take a look at this page: ... loops.html

Re: Using more than two sensors

Posted: Fri Aug 23, 2019 7:37 am
by martink
I agree with Doug's opening line (the conclusion!), but the reversing loop part of it should work fine. I assume you have wired each loop through a rectifier so trains will always move in the same direction, relying on the one-way point to put it on that track. If the sensor is then placed near the end of the section, the controller will have the correct direction set for the main line when the train needs it.

Seriously, if you aren't happy with dismantling a sensor to see how it is wired and then doing some fun electronics to combine two, your best bet is to simply use those two control boxes as before. After replacing the damaged one, of course.

Re: Using more than two sensors

Posted: Wed Mar 04, 2020 4:30 pm
by davidmatthewson

ISTR a while ago you were playing/going to play with some home brew IR sensors...did you ever get them to work?



Re: Using more than two sensors

Posted: Wed Mar 04, 2020 7:19 pm
by dkightley
I've used IR sensors for quite a while now...initially on a microprocessor control system that a T gauge user Martin ( username martink ) designed and built for his T layout, and then offered me a copy of the system. It worked very well for a year, but was superseded by my DCC work.

An LED planted underneath the track with a 3 or 4mm hole and it successfully used the ambient light from the layout lighting. It worked at most shows....only being thwarted by the overbearing brightness of a show being held in a giant marquee in mid-summer!

On Saltash, as all bar two sensors are "behind the scenes", I've 3D printed gantries that hold white LEDs to provide the light source, allowing me to use smaller holes to channel the light. I've not run them in anger.....but in test, they work very well, and I've connected then to MERG multi-way feedback input boards to feed JMRI software on a laptop for automation purposes. On the Saltash thread there's a photo or two of a gantry...and its components.

For the two "display side" sensors, I've used low-power laser beams (like the ones you see on bar code reading tills in shops) shining across the track, with the train breaking the beam. These also are currently untested in anger.....but do work very well!

Still to be experimented with, I have the electronics and relevant parts for using RF ID tags attached to the underside of locos so that individual locos can be detected...and again, feeding into MERG electronics to provide feedback to the JMRI software....

Re: Using more than two sensors

Posted: Thu Mar 05, 2020 8:26 pm
by davidmatthewson
Thanks Doug - interested to see how you get on with RFID tags- I used these a while ago for an 009 demo but ISTR they would be a bit fat for T..


Re: Using more than two sensors

Posted: Thu Mar 05, 2020 11:26 pm
by dkightley
There's a piccie of the tags I've got on another thread: viewtopic.php?f=10&t=1675

They'll fit nicely in a slot in a loco under belly.

Re: Using more than two sensors

Posted: Sat Jul 17, 2021 9:55 pm
by dino956
Check out the new precision detectors from They have both an adjustable range (1-150 mm) and an adjustable detection width (10 mm for N) within that range. This combination can be used to effectively sense trains on parallel tracks. There is also a timeout adjust to eliminate errors caused by the spacing between wagons in a train. They claim to be unaffected by ambient light sources. They are designed for N Gauge but should work for T. Here's a link to the introduction video

Re: Using more than two sensors

Posted: Sat Jul 17, 2021 11:24 pm
by davidmatthewson
Thanks Dino - interesting.