Casmer

Looks like this might work for me thanks. I think I may even to be able to use multiple to get more than 4 devices off of 3 pins, instead I can get use 4 pins and control a few more devices. by adding more of these 74HC4052's together.

Never mind, I have that

SPI.Configuration conf = new SPI.Configuration(Pins.GPIO_PIN_D10, false, 1, 1, false, true, 1000, SPI.SPI_module.SPI1);

spiPort=new SPI(conf);

spiPort.WriteRead(buffer, buffer);

I used pin 10 for the select pin.

For those that are as new to this as me, the SPI pins are pins 12 (data - D0) and 13(clock - CLK). above I selected pin 10 as the select pin. (CS)

Is there a fully fleshed out example of this? Something that includes the read steps?

Refer to page 6, bottom circuit.

The LM working principle is based on a oscillator. Its output (pin 13) is going though a capacitor to the probe (and pin 10), which acts essentially as a resistor to the ground. The higher is the fluid conductivity, the lower will be the resistance. This phenomena is due by the free ions available in the fluid, so it depends on what's in the fluid itself.

Anyway, on pin 10 there is a pulsing signal, having the same frequency of the reference oscillator. Since the capacitor and the fluid-resistor pattern behaves like a high-pass filter (in the frequency domain), by modifying the fluid-resistance also the amplitude on pin 10 will be related to it.

The "detector" stage acts as a level detector, so that only when the amplitude is above a certain threshold, the signal can flow through this block.

Now we're on pin 9 and the signal is *still* oscillating, but we don't want that: we just need a "stable" signal to reveal the successful detection. That's the way the capacitor on pin 9 is very important: it acts as a pulse smoother, and levels most of the ripple that we don't want.

At this point, the game is over: when the detector is able to flow the signal to pin 9, the cap gets it smoother and the final transistor will be polarized. Since the emitter (pin 12) is to the ground, the transistor polarization means that the pin 12 is tied low as well.

Hereinafter, the Netduino wiring is as we discussed above: nothing has changed.

 

My initial error was about *HOW* the LM yields the detection: I believed on a simple "stable" output, but it wasn't. Without the smoothing cap, the output is toggled at the same frequency of the reference oscillator.

 

Tell me whether that's clear enough.

Cheers

I just plain did not see the Capacitor on pin 9. How close to 20uF do you think I have to get for it to work? thanks again!

Sorry, Casmer, it's my fault! I didn't not check the datasheet, but I referred only to the schematic above.

The circuit you used is for testing, and without smoothing capacitor, will output a square wave, not a continuous signal.

You should consider the schematic at page 6 (bottom), instead. However, the resistor/diode/transistor group depicted at pin 12 is not necessary, and everything we discussed about the interface with the Netduino is still alive.

Cheers

You are referring to the second transitor for controlling a solenoid? that is what is on page six. Also, how would that create a constant output? does that have to do with out transistors switch on or off that I don't know about? I though it would do the same thing all over again.