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There was a discussion some time back about using photosensors for chuff input in TMCC/RS4 upgrades. I ordered some RPR-220 reflective photosensors to try out not long after. The idea is to trigger fixed chuffs from a driver as opposed to using a tender wheel with magnets using the old 2 chuff/tender wheel dia. = n chuff/driver dia. where n chuff is close enough but sometimes too low.

My current 3rd Rail J1a project seemed to be a good candidate for a bit of analog electronic tomfoolery. I am using a classic Lionel RS4 3 board setup with the chuff input on the m/b. This input reads 5VDC when open. The m/b I have is fairly similar to some of the small TMCC steam with tethers from the early 2000s.

In any case, tonight’s little experiment is promising. Here’s a vid of the first problem encountered:

Here’s a chicken scratch of the circuit I cobbled up:


I was wondering if anyone else has experimented with these. There are quite a few smaller versions out there. In any case, seems promising!


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Norton, I am planning on using the sensor on spoked drivers, painting the backside of the flange black with 4 silver stripes for a trigger. I did play around with shining a flashlight on my sketchy setup and it didn’t seem to affect the sensor.

I will see what happens when I try to set it up. Maybe a small hood made out of brass or styrene could help if I encounter some issues.

I was kind of surprised the sensor could respond to the 60Hz of the half wave dc powering the IR LED. At least that’s what I think was triggering the machine gun chuff.

Random triggers from ambient light will depend on how much IR is in the light source. Cool LED and fluorescent likely won't be a problem. incandescent maybe, sunlight for sure as some fellow club members who used my circuit found out when we setup at a local fairgrounds. Those detectors are very fast, much faster than 60 hz. Being able to mount the detector on the flange will depend on how much is the way. Usually the cast on leaf springs are the problem. On my last install I had to install the sensor below the frame.




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Last edited by Norton

I spent a bit more time experimenting with the RPR-220 but decided to install one of John’s CGs. I am using one of his nice little 5V power supplies (no smoke so no Super Chuffer to get 5V from). I was able to mount the power supply on the tailbeam and had a nice unused smoke switch location for the cal switch, accessible below the flywheel:


I used the ground light output of the CG in the cab by the engineer so he can check his OGR posts before heading out. This is an 0402 LED, the one above the backhead is always on with track power:


Here’s a quick little vid:

I may revisit the RPR-220 on another project. I found I could actually trigger the chuff from a striped axle but need a reliable mount that would allow me to adjust the sensor’s position for best response.


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The filtered DC for the IR LED seemed to cure the machine gunning. I was just being a wise guy powering it with a diode and a 470ohm resistor for experimental purposes. My biggest challenge is fixturing the sensor in a way that it would be adjustable. I figure it could trigger off a driver or an axle for a no-math proper chuff rate. I am so close to getting a 3D printer to make adapter parts for things like this. I was just fartin' around with TinkerCAD to see how quickly things could be cobbled.

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