Discussion in 'The Projects Forum' started by abhi999, Feb 5, 2009.

1. ### abhi999 Thread Starter New Member

Feb 5, 2009
3
0
Hi everyone,

I am not a pro in electronics. In my spare time I build electronics gadgets. This is like hobby for me. I wanted to build a water level indicator and searched through the net for one. I got a good circuit diagram (here is the link http://www.electronicsforu.com/efylinux/circuit/cir105.htm)from a good site and started to build the thing. After two days of work I finally completed the circuit. It works fine but I a stuck in one place.

This is the Circuit Diagram http://www.electronicsforu.com/efylinux/circuit/cir105.gif

The circuit is working fine except the LED marked LED1 does not light up at all. Normally LED1 should light if the water level is below level L2 but above L1 thus connecting L1 metal strip with the Long Main Lead.

I have checked the circuit. The problem I noticed here is that the LED1 is not getting the Minimum Threshold Voltage to light Up. It is getting around 1.25volts which is insufficient for lighting up the led (this Should be anything in between 2.5 to 5.5volts).

On more thing happening here is that when water drops below L1, the voltage across the LED1 drops to half (0.6volt) now the circuit is built in such a way that this should happen ; only the drop should be from (2.5 to 5.5volt) to around 1.25volt.

So as per my inference goes the problem is this :

The voltage across LED1 is 1.25volt instead of 2.5 to 5.5volt when water level is above L1
The voltage across LED1 is 0.65volt instead of 1.25volt when water level is below L1

Rest of the LEDs are getting around 5.5volts each and are working fine.

Now can anyone help me out of this problem please. I am unable to figure out where the problem might actually be.

Abhi

2. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Connect another diode in series with D1 between D1 and L1. Then disconnect Led1 from where it is and connect it directly to L1. Also, put a protection diode across Led1.

However, I don't suggest you to use this circuit because the metal conducts in the water will rust and dissolved with time. It would be better to use a plastic rod which can float on water. Then put a pipe in the water tank (perpendicular) with a diameter just for the plastic rod to be able to move up and down inside the pipe. Then put the plastic rod in the pipe and by measuring the height the rod rises you can detect the water level.

Another way, is to attach a metal rod or plate inside a plastic pipe and close the plastic pipe on the bottom as water can't enter inside it. Then put a metal stripe along the height of the tank (if the tank is made of metal use it as the plate). This configuration is actually a capacitor and as the water level will arise the capacitance will change. If you apply an AC voltage across the meta rod (inside the plastic rod) and the metal strip outside the tank (or the tank itself it is made of metal) then the AC current will vary according to the water level. I have never tried this method because I have just though it but it should work.

Last edited: Feb 5, 2009
3. ### abhi999 Thread Starter New Member

Feb 5, 2009
3
0
Hi mik3,

Thank you very much for your solution. I will straight away go and try what you said and post the result here.

As per your suggestion of not using the thing because of rusting, I completely agree with you but I need it like that because the water tank in which i will fix the thing is on the terrace and therefore its pretty annoying and inconvenient to rush to the terrace to check the level each and every time. Therefore this kind of a gadget is the best solution for the problem as setting up the plastic level indicator wont help the cause. As far as the melting/rusting of the conductor plates is concerned, I have used thick Brass Metal Nuts & Bolt for that. This is surely going to take a while to rust away, and surely when it does, that would require only a couple of hours of time and a couple of trip to the terrace to replace them with new one. Now this is definitely better than running up there each & every day for at least two times to the terrace to check the tank. This is the reason why I am Inclined to use the thing.

Thanks Very Much

Regards

Abhi