Chuff Cam circuit ? Where's the ground?

[gmpullman]

I have a few brass engines that I'm preparing to install sound decoders in. I have a few TCS WOW sound model 1513 decoders that have a hard-wired tan wire for the chuff sensor. I'll make a bronze wiper to contact the cam.

These engines have a four-lobe cam pressed on to the axle so they are going to complete the circuit through the engine chassis, and then on to the right rail.

So, I'm wondering what the "other side" of the chuff cam circuit is supposed to be? The diagrams for both WOWsound and Tsunami only show one wire to the chuff sensor.

Will it be OK to "ground" the chuff cam wire to the rail? Otherwise, what wire should the chuff sensor use to complete the circuit?

Thanks, Ed

[mlehman]

Ed,
I don't know the answer to your question, but don't ground that tan wire to the rail. That may just let the smoke out. Typically, I just tuck it away where it won't ground on anything of not in use. If to be used, hook it up to the cam and it should work. Why?

[DigitalGriffin]

It's grounded at the decoder.  But it will only work on DCC tracks, not DC in alternate power source mode.

[gmpullman]

Thanks, Mike and Don

I got a quick reply from Norm at TCS and here's what he said:

Hello Ed,

The cam will work with either rail to trigger the chuff or you can just use the auto chuff (default). Both are included in the WOWSound decoder. If you decide to use the cam, to enable it set these 4 CV's in order:

CV201 = 4
CV202 = 19
CV203 = 0
CV204 = 57

Best Regards

Norm Stenzel

Tech Support

267-733-3408 cell

Mike, I was a bit concerned about grounding through the axle, and thus the rail but TCS says it is OK. Some of my brass engines that are 20 or 30 years old have speaker holes in the tender floor and the square cam on one of the driver axles for sound. That's forward thinking!

Don, I have all DC conversion disabled on my decoders anyway. Thanks for your help,
Ed

[mlehman]

OK, now I've learned somthing. Knew it worked, was just clueless how. I'm a better safe than sorry sort, so good to know it's safe to do that.

[rrinker]

 Far as I know (not being a decoder designer or having access to anyone's schematics), the chuff sensor is just an input to the decoder's processor, a high impedence input, meaning there is a large value resistor between the outside world and the chip. So it needs to see a voltage relative to the decoder's ground, which is taken from one side of the bridge rectifier which is conencted to track power. So a conenction from either rail would work as stated, it doesn;t matter which. And there would be no danger in frying anything since the large resistance would limit total current flowing through the decoder

 At least, that seems like the logical way it would work knowing microcontrollers and the basic building blocks of decoders.

                 --Randy