Water level indicator

Thread Starter

endlasuresh

Joined Feb 11, 2010
19
I tried today to build a simple water level indicator, but failed.I bought all these were from shop except charger.
BC 547 transistor
220 ohms resistor
5mm leds
9v charger but it is giving 12v might be this is a big problem for failing project.

I connected everything as in the image, but two leds were lighted themselves from starting and the other 2 were lighting when i touched the transistor center pin.
after sometime all the four leds are lighting by themselves. I think transistors are dead due to 12v, but let me know where the problem happened.
I am thinking the shop sold are poor quality components.
 

Attachments

MisterBill2

Joined Jan 23, 2018
9,468
I tried today to build a simple water level indicator, but failed.I bought all these were from shop except charger.
BC 547 transistor
220 ohms resistor
5mm leds
9v charger but it is giving 12v might be this is a big problem for failing project.

I connected everything as in the image, but two leds were lighted themselves from starting and the other 2 were lighting when i touched the transistor center pin.
after sometime all the four leds are lighting by themselves. I think transistors are dead due to 12v, but let me know where the problem happened.
I am thinking the shop sold are poor quality components.
That image does not provide enough information to allow any useful advice to be offered. So the very best you will get is guesses.
 
Last edited:

KeithWalker

Joined Jul 10, 2017
1,933
The supply voltage not the problem.The BC547 will work with up to 40V across the collector to emitter. It is a badly designed circuit because it should have a resistor in series with each transistor base to protect it from being overloaded and damaged. The maximum Vbe is 6V. With no base current limiting resistors, the bases are exposed to the supply voltage through the liquid.
I suspect that all the transistors are blown. You can check each one by connecting each input sense wire in turn through a 10K resistor to the supply. If the led does not light, that transistor is dead. If you rebuild the circuit, add a 10K resistor between the base and sense wire on each transistor. Make sure that the end of each sense wire has at least 1/4" (6 cm) of bare wire exposed, bent to be parallel with the surface of the water, to give it enough area to make good contact.
NOTE: Pure water does not conduct electricity so this circuit will not work with distilled water or clean rain water, and may not work with filtered water.
 
Last edited:

Audioguru again

Joined Oct 21, 2019
3,634
Your transistors are missing a resistor from base to emitter to turn them off. That will help prevent the wires at the bases from being antennas that pickup mains hum and most radio signals near you.

A cheap power supply has no voltage regulation. Its voltage drops to near its voltage rating when its current is at its current rating.

Calculate the LED current. 12V- 2V for a red LED is 10V. Then the current in each LED is 10V/220 ohms= 45mA. The maximum allowed current in a 5mm LED is usually 30mA so yours might have burned out.

Buy electronic parts at a real electronic part distributor like Digikey or Farnell because your local shop might buy cheap fakes from ebay.

You showed a tiny photo of a bunch of parts. Next time please post a real schematic.
 

Thread Starter

endlasuresh

Joined Feb 11, 2010
19
There are lot of videos on YouTube but people mentioned it worked for them.
Here is the video
I'll try to rebuild them with 2 leds as you told in above posts and see.
 

BobaMosfet

Joined Jul 1, 2009
1,878
Your transistors are missing a resistor from base to emitter to turn them off. That will help prevent the wires at the bases from being antennas that pickup mains hum and most radio signals near you.

A cheap power supply has no voltage regulation. Its voltage drops to near its voltage rating when its current is at its current rating.

Calculate the LED current. 12V- 2V for a red LED is 10V. Then the current in each LED is 10V/220 ohms= 45mA. The maximum allowed current in a 5mm LED is usually 30mA so yours might have burned out.

Buy electronic parts at a real electronic part distributor like Digikey or Farnell because your local shop might buy cheap fakes from ebay.

You showed a tiny photo of a bunch of parts. Next time please post a real schematic.
Article & schematic his project is based on:

https://envirementalb.com/simple-water-level-indicator/
 

Thread Starter

endlasuresh

Joined Feb 11, 2010
19
The supply voltage not the problem.The BC547 will work with up to 40V across the collector to emitter. It is a badly designed circuit because it should have a resistor in series with each transistor base to protect it from being overloaded and damaged. The maximum Vbe is 6V. With no base current limiting resistors, the bases are exposed to the supply voltage through the liquid.
I suspect that all the transistors are blown. You can check each one by connecting each input sense wire in turn through a 10K resistor to the supply. If the led does not light, that transistor is dead. If you rebuild the circuit, add a 10K resistor between the base and sense wire on each transistor. Make sure that the end of each sense wire has at least 1/4" (6 cm) of bare wire exposed, bent to be parallel with the surface of the water, to give it enough area to make good contact.
NOTE: Pure water does not conduct electricity so this circuit will not work with distilled water or clean rain water, and may not work with filtered water.
I will check tomorrow and see to fix the problem. Thanks for your advice, but I didn't get what you meant for 6cm in parallel.
I am building for 500 liters water tank.
 

KeithWalker

Joined Jul 10, 2017
1,933
I will check tomorrow and see to fix the problem. Thanks for your advice, but I didn't get what you meant for 6cm in parallel.
I am building for 500 liters water tank.
My mistake . I meant not 6cm but 6mm (1/4") . At least that much wire should be exposed in the water to get a good contact. If it is bent into an "L" shape with the bare wire being the base of the "L" you will get the best resolution. If the water tank is metal, make sure the wires don't touch the tank.
 

Audioguru again

Joined Oct 21, 2019
3,634
The video is probably a fake since the "220 ohms" resistors appear to be only 22 ohms which will quickly burn out the LEDs if the battery is any good (maybe it is almost dead?).
Notice that there is almost no bare wire in the water that might be acid instead of water.
 

Ian0

Joined Aug 7, 2020
3,463
The maximum Vbe is 6V.
That's actually Vebo - the maximum reverse base-emitter voltage. Because there's a diode between base and emitter, you won't get more than a volt of forward voltage before it fails due to over-current.
With no base current limiting resistors, the bases are exposed to the supply voltage through the liquid.
Not unless that liquid is mercury - even salt-water won't pass enough current to exceed the maximum base current of 200mA.

I am building for 500 liters water tank.
This project really isn't much use beyond a demonstration. In real life the sensor wire will quickly dissolve due to electrolysis, and you will end up with metal ions in the water.
A float switch or a tube with a pressure switch at the end (as used in washing machines) will be much more reliable for a big water tank.
 
Top