Arduino Based Water level Controller - Voltage drop problem at sensors

[snmjack]

Hi, my name is swapnil. I am trying to make a water level controller using arduino. I refered many circuit ideas for different website and made my own design. Simulated it in Protues and it worked fine. Also i designed my PCB in eagle and started implementing.
Everything was going as per plan, but when i tried to test the input sensors voltage, i got major voltage drop due to water acting as resistance between the sensors.
For sensor - I used a PVC pipe, in which Cat 6 LAN cable is inserted. One wire of LAN cable is connected at bottom of PVC pipe with a stainless steel metal. This wire is also connected to 5V supply through board. Same way other sensors are connected to different levels of PVC pipes. Now when water rises till 1/4 tank full sensor, arduino will get the voltage at its digital input pins (Because of water, 5V sensor and 1/4 tank full sensor will get short).
Now the problem here is, water is conductive but with high resistance since its not much salty, so instead of getting 5V at 1/4 tank full sensor, i am getting around 2-3 volts.
My board is also ready and sensor set for both Below tank and overhead tank are both ready, and my program also works fine. but i am stuck at this voltage drop problem.
I had one thing in mind, what if i use a intermidiate circuit betweent he sensor set and board, which will detect any voltage above 0V and give output 5V. But i am not getting any such circuit ideas to build one.

Anyone have any idea.. how to tackle this problem.

 

[KlausST]

Hi,

the complete construction is not clear to me.

But it seems you work with DC voltage. This may sooner or later wear out your electrodes.

****
The sensing voltage problem is caused by:
* current drawn from the electrode
* sensor_dependent resitance = sensor size.

Therefore I see two solutions:
* reduce the current by using an amplifier
* increase the sensor size.

Klaus

 

[snmjack]

Hi, Thx ...
I have used stailess steel screw as electrodes. So there are 5 electrodes in the tank in vertical position to detect 5 levels. As you can see in the proteus image file, i have also connected a LED in series of 220 ohm resistor. So one leg of sensor goes to arduino Digital input pin and other leg go to LED, to get an visual indication of the level reached.
I did not understand your suggestion of reducing the current. Should i increase the value of 220 ohm resistance or any additional circuit?

 

[KlausST]

Hi,

As you can see in the proteus image file

No, I can´t see this...
*****

I did not understand your suggestion of reducing the current. Should i increase the value of 220 ohm resistance or any additional circuit?

In your circuit the electrodes should carry the current of a LED?
--> don´t do this. Soon your electrodes will be gone (it doesn´t care wich material they are)

Drive the LEDs from an arduino output.

Then the electrodes current is just a few microamperes to pull the arduino input high or low.
Additionally you may use the internal pullup. you may switch the internall pullup OFF most of the time ... this additionally decreases electrode current and increases electrodes lifetime.
Just switch ON the pullups a short time before you read the electrodes state.

Don´t forget to install some ESD protection. Maybe use a capacitor as low pass filter. (depends on read cycle time)

Klaus

 

[snmjack]

I have attched a image file for transistor logic... will this logic work?

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Thx... i have attached the proteus files and arduino source file and hex file. driving LED directly from arduino will require more output pins. Can you please check , what all changes are required in the design?View attachment WLC EDA.7zView attachment WLC EDA.7z

- - - Updated - - -

please see attached proteus and adruino files... suggest changes that need to be done. FYI.. the code and proteus files works without any error.

 

[BradtheRad]

I have attched a image file for transistor logic... will this logic work?

Typical setup for NPN biasing. Output is taken at collector leg.

The sensor (or touch contacts) can be one or the other side of the potentiometer. Detach the potentiometer at one end, depending on how you want output to respond when contact is made.