water degtection frequency

What frequency would be recomended for detecting water ?

Read through this. Its higher than you think.

how do you want to do it? You could stick 2 probes in the water and measure the change in resistance between them. This requires dc (10V maximum). If you wanted to mount something above the water surface and measure the distance, you could do this with ultrasonics (40kHz) and measure how long the ultrasonic wave takes to bounce back to the transmitter and do a 'time of flight' calculation

It doesn't matter as long as it's high enough to prevent electrolysis, I'd recommend using a frequency above 20kHz so you can't hear it.

EDIT:

Electronworks,

You do realise that using DC causes electrolysis which can cause corrosion??

well I'm using the 1 MHz that the pic provides as it's available anyhow, thing now is I'm having trouble rectifying my output and keeping an average voltage of 0 (AC) through the water to stop electrolysis

If you run the signal through a series capacitor, then you are guaranteed there will be no net DC current.

Thunderchild said:

well I'm using the 1 MHz that the pic provides as it's available anyhow, thing now is I'm having trouble rectifying my output and keeping an average voltage of 0 (AC) through the water to stop electrolysis

Click to expand...

I suggest you take another look at the circuit I posted awhile ago on the other forum, here it is again.

I know you're using an MCU so it won't be the same but the basic capacitor, rectifier and pull-down configuration shouldn't need to change.

How long are the leads?

If the capacitance of the leads is significant compared to the AC coupling capacitors then it won't work because the parasitic capacitance of the leads will cause a current to flow, giving a false positive.

yes I realized after my error i forgot to put a cap on both probes, yea our supplier is still getting his water detection pumps all wrong and we are in a massive mess. people seem to not appreciate my critism of the supplier as he naturally MUST know more than me. well I've decided to put that to the test ! considering this bloke does this for a living it is amazing we have such ,massive failures instead of altering his crappy circuit he is now potting the whole thing, really i begin to wonder if he designed it himself !

I'm having to use a uC because to stop the pump from burning out certain running and rest times have to be set otherwise I'd use comparators or logic gates, it seems very easy to get 1 MHz @ 5 V through water and it can be detected and rectified to 3-4 V DC again so very easy to pic up and set another circuit off by in my case I'll use the ADC of the uC. if the probes are pulled out of the water it goes dead so I really can't see why his design is so fragile as it it can run and never stop or just not run at all.

more experimentation going on tonight