I agree Stan, the only reason i am perusing this is we run a lighted caboose at the end of every train, and the passenger trains are all lighted (being converted to LEDS).
that module looks interesting, wonder how i could get it between the rails, maybe unmount them from the PCB and sink them into the board?
Well, if your passenger cars have been converted to LEDs, it's likely they each draw far less than 5 Watts of an incandescent caboose. For example, the Hennings LED passenger car module might be set to as little as 10 mA. So using the ACS712 eBay current sensor module, that would generate a voltage output of only 0.1 V/A x 0.01 A = 10 milliVolts when a passenger car is running by that block sensor. 10mV is arguably difficult to easily detect. I understand a block can be longer than 1 car length so you'd be detecting multiple cars and hence the current to be measured would be higher, but I think you get my point.
Anyway, the emitting LED and detecting sensor on the modulated eBay module are of the 5mm ilk. So, yes, you could drill 5mm holes in your track bed or something like that.
Note that the "trick" to this modulated IR infrared occupancy detection is the integrated IR detector chip tuned to 40 kHz or whatever.
These are 3-terminal chips with the photodetector and all the electronics to detect just a pulsed/modulated IR reflection. So if you are configuring a system/layout you only need one generator of 38/40 kHz driving multiple LEDs all pulsing at a common frequency...and one of these 15 cent IR receiver modules detecting the reflections when a block is occupied. Note that the current detection method might generate a somewhat difficult to detect millivolt range output whereas this IR Receiver chip swings a full 5V or so between detect and no-detect!
Sounds like it might be worth my wild to rewire for isolated blocks! The photocell logic was time consuming, and the IR seems like too much tech for most of the club members. My saying "K.I.S.S"
Agreed. I'd think the effort to create isolated outer-rail blocks vs. isolated center-rail blocks would be similar. That is, you'll be creating gaps between track sections and running additional wires to the newly formed electrical "islands". An obvious advantage of the isolated outer-rail method is the amount of current flowing when the block is occupied is negligible...measured in the, say, milliAmps. The isolated center-rail method using current-sensing carries the full current of the train which can be in the Amps. This has implications on the type of wiring used. And has been discussed there are tradeoffs in current-sensing technique. The outer-rail method has negligible current flow as you are simply detecting the presence/absence of the common outer-rail voltage supplied via one or more wheel axles - a relatively simple circuit.
Agreed. It's the same effort as center rail gaps. The relays we had under the layout for the first test of isolated blocks were from Azatrax, he has great products but don't think these were the right thing for this layout.
Ive seen you're previous threads with the one channel boards for about 2$
I have a 8 channel Arduino relay module. Just a little confused at where to hook the wires up to. (Coffee hasn't kicked in yet)
christhetrainguy09 posted:...I have a 8 channel Arduino relay module. Just a little confused at where to hook the wires up to. (Coffee hasn't kicked in yet)
Is this a question or a statement? 
I seem to recall drawing up a diagram for another thread on how to use these $1/channel multi-relay modules but can't seem to quickly find it.
Anyway, if you're seeking suggestions on how to hook it up for isolated outer-rail, I suggest starting another thread to keep the hi-jacking police at bay. 
What I'd want to know is:
1. What voltage is your 8-channel module (5V, 12V, etc.)?
2. Is it "hi" or "low" level triggered? Or what is the eBay listing #.
3. These modules do not have any timing or delay to demote or mask intermittent axle contact (relay chatter) when the first few axles enter the block or when the last few axles exit the block. Is this feature of interest - which would add, say, 25 cents per channel and assembling a few components (capacitor, etc.).
I will start another thread later tonight. That should keep the hijack police happy.
Hi. I see there has been an interesting discussion here. With the ACS712 I guess I can eliminate the optoislator, but what about the filters for compensating for "dirty track" that may cause flickering in my output signal? Would I then need an Arduino to capture the output and then perform my signal logic via software? I was once a software engineer so this is not a daunting task for me. This was something I considered but decided against given the complexity of my signal modules and the very fact that Arduino cannot handle the number of inputs and output needed for some of my modules, let alone issues when wiring up an Arduino (i.e. solder bridges destroying inputs/outputs). What I see here is a possible software solution which I ruled out, however will the ACS712 provide the needed output voltage to drive my signal logic if I go with the hardware solution (i.e. NAND gates) that will be part of my design. My guess is that it does not.
I know that the 1.4 Volt "tax" is a downside. I am reluctantly willing to live with that.
Actually, the ACS712 is not a good match to your application. It is a linear sensor which means you get a voltage output proportional to the measured current. This comes at a cost - both the IC chip (relative to a cost of a bridge-rectifier) and, to your point, additional circuitry to convert the output to a yes/no digital signal as needed by the downstream circuitry. It appears the 1.4V "tax" and arguably punitive power dissipation are acceptable so really all I can say is thanks for sharing! 
One observation about the thread topic of "current detectors". From what I've seen the big effort in block current detectors is for 2-rail applications like HO where they don't have the luxury of the extra isolated rail for "free" occupancy detection. 2-rail being generally DC, the bridge-rectifier and ACS712 operate/detect DC currents as well as 60 Hz AC and high-frequency DCC. I suspect if 2-rail had historically been 60 Hz AC, there would be more published circuits taking advantage of doughnut current-transformers as occupancy detectors without the 1.4V "tax". Not quite apples-apples but we all have current detector circuits protecting our safety - the GFCI (Ground Fault Circuit Interrupter). Generally implemented with a low-cost application-specific IC chip, it is a clever circuit which can detect remarkably small AC currents generating what amounts to a yes/no output.
If I was to use an ACS712, software would need to sample the output. That sample would be in the form of a loop that would check the output say 1000 times. That would replace the filter. In order to achieve the voltage needed to drive the logic, that resulting output from the loop could be fed into another softwate program that drives an Arduino output signal which could be 5 volts DC. That output could then drive the signal logic via hardware or software. Just another way of achieving the same goal. The advantage here is that there would be no 1.4V drop. I may have considered this, but all 123 detectors are now wired and tested.
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