Can CTMU/ADC be used to detect metal?

[large_ghostman]

Just thinking a few things through and it got me wondering, the set up is say a model train set with inductors between the rails (smd and small), now I now if you put a clocked pulse through an inductor them pass metal over it the frequency changes. There are a few on the net based around WDT etc, and I have done one with a timer etc.
This got me wondering, supposing you wanted more detectors then you would need something else. Do you think the following would work, the CTMU detects the charge on a cap over a sampled time. Depending on that charge determines if the capacitance has changed. So could the same be done using inductors connected to the CTMU channels?
Pass say a fairly high frequency low voltage/current at low duty cycle through the inductor and measure with the CTMU, no metal and the reading will be what ever charge has accumulated, pass metal over the inductor and would this alter the amount of charge by stretching the frequency or duty cycle therefore changing the amount of charge read by that CTMU channel. Obviously you set the CTMU to take readings at a set time period via timers so this is constant.
Thoughts ?
The distance between inductor and moving metal is only 2-3mm so that bit should work. If it does work then there are chips that have a good number of captouch channels and this would make it viable to have large numbers of train detection units along a track.

OK now explain why it wont work

have I tried it? I dont want to say yet, first I wont to get reactions

 

[JonSea]

Don't know if this will work, but another idea is to use cap-sense switch technology. Some of them can proximity as well as touch, so they should detect a metal train car passing over.

 

[large_ghostman]

Don't know if this will work, but another idea is to use cap-sense switch technology. Some of them can proximity as well as touch, so they should detect a metal train car passing over.

I think thats the same kind of thing, so looks like I am on the right track I didnt know until this morning but one of the Gecko dev boards I have uses a small inductor for metal detection, it uses a similar cap sensing system to microchips, so I am guessing it is doable! On the dev board it will only sense metal less than 4mm away, but to be fair the board is running at 1.8V for the moment.
Dads project is passed the first stage so I am hoping he will no longer need the kits! Now that would be like Christmas!!!

 

[JonSea]

I had wondered if CTMU was a variation of cap-sense but didn't bother looking it up. Sometimes, I can be lazy too

Hmmm...a pile of stuff suddenly available to use is a good thing!

 

[large_ghostman]

CTMU is microchips trade mark for Charge Time Management Unit, or Cap touch to anyone else. Actually to be fair they have a dedicated peripheral to do what you would do with a ADC to get the same result. Its just a precision current source and auto this and that, it sits on the ADC channels