Thanks ken I will bench test it tommo at my end ...but when u tested it what was the time delay coming during turn ON

 

~2.5 seconds on-time at power turn-on, and 5 second delay after water is removed. Changed R3 from 1.2MΩ to 1MΩ and got 3 seconds at power turn-on.

Ken

 

Dear KMoffett,


I have to make one modification in this circuit on urgency basis.I want initial time delay 5sec .Situation is like this :
Initial time delay after turn on =5sec
Then when we dip electrode in water then there should be 5sec delay before detecting the presence of water and then the lamp should glow .

In short I want there should be initial delay in starting before detecting presence of water..

Is that possible ?

Waiting for urgent reply

Thanks in advance

 

Why? And why urgent?

Diagram your timing.
Indications on power-up with no water present.
Indications on power-up with water present.
Indications if water detected some time after power-up.
Indications as water is drained after power-up.

Ken

 

So, whats the status of the design?

Ken

 

Dear KMOffett,

Thanks for your kind support

I would like to know one thing if I want to remodify this circuit with following specs which need to be fulfilled.

With Water detected =11.99V i.e(supply voltage-0.5V min)
With fuel detected =0.5Vmin to 1.8Vmax
Supply voltage =10.5Vmin to 16Vmax
with LOAD rating of LED =1.703V able to drive this circuit
Initial self test after key ON is not required in this case

What all modifications need to be done in that case so that I can meet this requirement as in present case with water detected it shows the saturation voltage of IC .Please correct me if I am wrong.So Do I need to change the IC suiting this requirement .

Please give your valuable input for the same.

Thanks in advance

 

I'm assuming that you want a simple circuit with only an LED indicator. Attached schematic should work. Note the change of the inputs to the LM311. I have not bench tested this.

Ken

 

Dear Kmoffett,
can you please let me know with this IC output current is 40mA and in your sensor circuit diagram can you please tell me maximum output current for this.

Waiting for your kind reply

 

Page 5, near the bottom.
"Output Source Current": Minimum=20mA, Typical=40mA.
"Output Sink Current": Minimum=10mA, Typical=20mA.

My circuit, in Post #87, uses a "sink" output.

Ken

Ken

 

dear KMoffett,
Please find enclosed one circuit which i made for water sensor new...with Power MOsfet for the details which i mentioned in my last post..with water condition i.e 100kohm output is 11.3V or greater and in fuel condition i.e 1Mohm output is 0.5 to 1.8V.in this circuit 100kohm represents water condition and in this situation i get output voltage 12V and in fuel condition i get 1.009V well within the range.Please give your view about the same and disadvantages which will be there.Will this idea work for small cars ?waiting for ur reply about circuit and protection circuit.

 

this is the circuit

 

The problem is that MOSFETS do not switch on and off as nice trip points like the comparator circuits. They go from barely conducting to saturation over a wide range of input voltages. And, that can vary from transistor to transistor. Plus, the turn on point will vary with the power supply voltage. And, putting a resistor between source and ground will cause negative feedback that will make the problems even worse.

Ken

 

so according to you we cant use mosfet all alone? cant we modify this circuit itself.please provide some solution for it.Or can we simplify IC circuit for the same.Kindly let me know.

 

What's your goal here? Size? Parts count? Cost? Curiosity?

Simplify the comparator circuit means giving up what you have previously requested.

Ken

 

cost .I have made one circuit wid comparator i need a more simple circuit than this one is it possible with this mosfet ?

 

If you can find an "automotive rated", logic-level, P-channel MOSFET it might work. The turn-on will likely be less predictable that the comparator. The turn-on will probably be a gradual, not complete OFF to complete ON, and may be flickery with any motion. But it's worth a try.

Google: p ch mosfet automotive logic level

Also, did you want a high or low output on this one when water is detected? I was assuming High. N-Chanel if you want Low.

Ken

 

If you can find an "automotive rated", logic-level, P-channel MOSFET it might work. The turn-on will likely be less predictable that the comparator. The turn-on will probably be a gradual, not complete OFF to complete ON, and may be flickery with any motion. But it's worth a try.

Google: p ch mosfet automotive logic level

Also, did you want a high or low output on this one when water is detected? I was assuming High. N-Chanel if you want Low.

Ken

with water detected output goes high .

 

Why p channel only...Why cant i use n channel mosfet in case of water detected condition (output is high)

 

First...what is the output going to pull high when water is detected? What is the load?
Second...I'm still under the assumption that one of the detector electrodes is grounded, not + battery.

Ken

 

The detector electrode is grounded.

Load is ECU output of sensor is pulled up by 2.61ohm resistance and is given to ECU