Troops,

There is a guy on ebay selling chips for detecting fluid levels. The item number is: 7539003779

He only wants 19 cents each plus postage (which is reasonable).

Here is a description of the part:

ULN2429A (1pc) Fluid Detector and Level Sensor IC NOS
This IC was originally designed primarily as an Automotive Coolant Level Detector. It may be used to detect the presence or absence of many types of fluids in automotive, home, or industrial applications - such as water, acids, wet soil, beer, wine, petroleum products, pop, you name it.  It is designed to be used in very harsh environments.

I showed this to Ed Anderson, who found a circuit for this chip at:

http://www.tinaja.com/glib/hackar1.pdf

While the pdf document is pretty long, the relevant pages are on pages 12-14. For your info, I've copied those pages here in the enclosed files.

In the write-up Ed found, the author wrote that conductivity makes the circuit work, making it suitable for keeping track of your radiator, expansion tank, etc.. However, the guy selling it on ebay has a very small and hard-to-read functional block diagram on the ebay page and claims that it will work for petroleum products. Beats me who's correct . If one of you verifies this one way or the other, please report back.

At any rate, for 19 cents plus postage, it's hard to beat.

Hey Rusty, what ever happened to that guy who had that bunch of optical sensors he was metering out on ebay a couple at a time?

Barry Gardner
Wheaton, IL