On December 19, 2005 04:29 am, Steph Smith wrote:
> found this site,
> http://hawthorn.csse.monash.edu.au/~njh/electronics/watersensor/
> and just wondered...has anyone
> a.seen it?

no, haven't seen it but it looks interesting.

> b.made simpler version?

it appears somewhat complicated for a water sensor.

> c.how easy/not! would it be with a newer PIC
> i.e. the 12F675

You don't have many pins to work with on the 12f versions.
For accuracy, you need to run a crystal and not the internal clock, 
since the internal clock is +/- a large percentage, but a crystal is 
considered reliable to 4 digits past the decimal point, and stable to 
about 5 digits past the decimal.
I would suspect you want the 12Fxx to have both an RX and a TX. The RX 
would be so that you could calibrate the 12Fxx so that it would be 
usable by any computer reading the output. On the other hand, you could 
probably live with just a TX capability and then correct at the 
computer.... therefore it would be a 12Fxx dedicated to 1 computer.

...so let's see... power takes 2 pins, xtal another 2 pins, let's 
suppose it's just a TX and no RX.... so that's 1 more dedicated pin... 
leaving you with 3 pins for measurement and what-not.

> (use the PIC to generate the 
> pulses for the capacitive sensor,lose the time-clock)

...I think you misunderstand how the circuit works. The pulses are 
generated via a 555 in this example.... however, if you are up to the 
challenge and a bit of ingenuity, you could probably do it a little 
differently using just the PIC.... hint: look at PIC Application notes 
regarding capacitance or resistance measurements.
hmmm, looks like you could probably re-instate the RX line after all.

Looks like you have yourself an interesting project.
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