Need help ???

Hello

I am creating a water level sensor.

As I shown on the attached screenshot the Low Level Protection as I marked giving me around 340mv when I measured it with multi meter all other levels are giving me around 2mv and they are working OK

they are all attached to arduino pro mini each to digital pin

They all worked before and something happen I am not sure what I replaced the 10k, 1k and even the BC548 transistor and I am still getting the same result. Where it said SENSOR OUT is RJ45 socket

They all work when I hold the VCC in 1 hand and the level wire with the other hand The Low Level Protection is working only when I touch VCC wire directly to it

Thank you

I have absolutely no clue what you are asking or what your schematic shows.

All I can determine is that the transistor connected to R5 is turned off, and the transistor connected to R6 is turned on.

Since you don't show what the collectors of the transistors are connected to or what the sensor is, I can't begin to guess if this is normal.

I have absolutely no clue what you are asking or what your schematic shows.

All I can determine is that the transistor connected to R5 is turned off, and the transistor connected to R6 is turned on.

Since you don’t show what the collectors of the transistors are connected to or what the sensor is, I can’t begin to guess if this is normal.

Hello

sorry. I attached new image

I am applying +5VDC to the circuit

Normally voltage should be +5VDC i.e “HIGH” But when water level rich >=0% voltage will go to -5VDC i.e “LOW”

The problem is that voltage drops only around 0.04mV when water level rich 0% all other levels are OK, but if I touch +5VDC to 0% wire then voltage goes to -5VDC i.e “LOW”

I have replaced the transistor and both resistors also the wires that goes to the water i.e CAT5 cable and I am still having the same problem

Thank you

If I am reading you correctly, and I'm not sure of this, you are not using the DMM correctly. The probe negative goes to ground.

So, what I see is a container with two electrodes plus a positive electrode. When the liquid level reaches a probe, the associated transistor should turn on.

What is the voltage at the base of the transistor, dry and wet?
What is the voltage at the collector of the transistor, dry and wet?

OP’s image

With no water in the container, measure the ‘voltage’ from the collector of 0% LLP transistor to GND; what do you read?

Add water covering the 0% sensor, what do you measure now?

Are you using tap water or distilled water?

Hi,
Using this diagram.


With the black/neg probe of your DMM connected to the gnd of your circuit;

  • Measure DC voltage at A, B, C , D with NO WATER and using the red/positive probe of DMM.
  • Measure DC voltage at A, B, C , D with WATER covering BOTH zero and 20% wires using the red/positive probe of DMM.

Thanks.. Tom... :slight_smile:
PS. Have you checked your tank probes for corrosion due to electrolysis?

TomGeorge:
Hi,
Using this diagram.


With the black/neg probe of your DMM connected to the gnd of your circuit;

  • Measure DC voltage at A, B, C , D with NO WATER and using the red/positive probe of DMM.
  • Measure DC voltage at A, B, C , D with WATER covering BOTH zero and 20% wires using the red/positive probe of DMM.

Thanks.. Tom... :slight_smile:
PS. Have you checked your tank probes for corrosion due to electrolysis?

Hello

Here are the measurements

no Water
A = 3.5mv
B = 4.97v
C = -345mv
D = 4.97v

in WATER
A = 0.753v
B = 9.2mv
C = 0.755v
D = 9.4mv

""PS. Have you checked your tank probes for corrosion due to electrolysis?""

It is not is the production yet

thank you

xlameee:
no Water
A = 3.5mv
B = 4.97v
C = -345mv
D = 4.97v

A, B, D: perfectly normal.

C, not so much - the main oddity is that it’s negative. Galvanic potential from two dissimilar metals maybe?

in WATER
A = 0.753v
B = 9.2mv
C = 0.755v
D = 9.4mv

Perfectly normal.

wvmarle:
A, B, D: perfectly normal.

C, not so much - the main oddity is that it's negative. Galvanic potential from two dissimilar metals maybe?

Perfectly normal.

What is that mean??? and How to fix it ????

Thank you

It is normally simply impossible to have any potential below 0V in your system - where you have a single power supply, and all negatives connected as GND.

Where two metals meet they can produce a voltage. That's the only way I can think of for a negative voltage to appear in your circuit (I'm assuming you're measuring correctly). These two metals, separated by some kind of electrolyte, then act as a battery, producing a tiny voltage. The current this can supply is very small as well, so a load much greater than a multimeter and it may basically disappear. Common examples of this include the lemon battery (copper/zinc) and the zinc galvanic anodes aka sacrificial anodes to protect iron in marine environments.

If there are other possibilities for such a voltage to appear, maybe someone else can chip in, I'd love to learn about it.

Not enough detail on your build to say where/how this could possibly happen. My best guess based on the little information I know is that it's some kind of reaction between the electrode and the container itself. A water film between the two can be enough, or some other leaky separator. The schematic as such doesn't give any clues.

hello

you are correct the sensor is assembled on the breadboard the only power supply going to this breadboard is from arduino 5v and GND

I am not sure if you can see much on the image I’ve attached

Thank you

OP’s image.

Replace the White and Red power wires, they may be bad.

After which, what voltage is measured between the Red and Blue power busses?

The is a Grey wire on the far right, what is that for?

Those green screw terminals have pins that are really too big for solderless breadboards.

It's probably not a super awesome idea to have the BASE pins floating like that (which they are) because they act like antenna and will respond to being touched by a finger just as much anything else or nearby electric fields.

Consider adding 47K ohm or so resistors between the Transistor BASE and GND and seeing if that helps.