> would this work through 60mm of cured concrete ?

Sure, but water / dampness spoils performance, so you'll have
to watch that. It's an easy circuit to experiment with, give it a go

I found the BiMOS CA3130/3140 worked well, better than
other common, and cheaper ;-( , amps of the time. It's a project
I'd like to re-visit at some stage (it can just join the queue), new
commercial applications have emerged

> I make concreto countertops with embedded clocks
>   and I would like to embed sensors in them.
> 
> See a not-very-good uTube video.
> http://www.youtube.com/v/dNsjyZ4yAHc

Couldn't quite make out the Hours / Minutes designation. Dual-
colour LEDs ?

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