Yes, it can be done...but...why? If there is water in the fuel tank you are looking at only one level, the presence of water below the fuel. What would be the tank fuel/water condition that you would need to detect two levels?

Ken

 

Anything new developments?

Ken

 

Well, the term "rail" when used in electronics is kind of an anachronism; people used to start drawing schematics by making horizontal lines for +V, ground, and -V, then start connecting components between these power lines. It started resembling railroad tracks, so they started calling them power "rails".

Yep, my teacher used to use the term "swing rail to rail" all the time. He had a couple of pet CMOS op-amps that he liked to use as they swung virtually to both rails.

Incidentally TI had a great doc (ref SLOA058) about how to configure op-amps in circuits if you have a single power supply etc - some good examples in there

 

Yep, my teacher used to use the term "swing rail to rail" all the time. He had a couple of pet CMOS op-amps that he liked to use as they swung virtually to both rails.

Incidentally TI had a great doc (ref SLOA058) about how to configure op-amps in circuits if you have a single power supply etc - some good examples in there

????????????

I was referring to payal.kellyyy's project requirements.

Ken

 

My first thought is that the layout of the PCB has an error. Can you post the layout...both sides?

Ken

 

The circuit in the schematic works. You verified it on a breadboard and in a simulator. It does not work on the PCB. That indicates that there is likely something wrong with the PCB. I can't help you diagnose a problem with something I can't see. Post the PCB.

Ken

 

OK. Are you saying the the circuit on the white breadboard always shows 0.172V on pin 7? Or, is that the circuit that works and the perf board one doesn't? I need to see the back of the perf board too, to see how you have connected the components.

Is the polarity of the electrolytic capacitor on the perf board wired correctly? The white band on the side is usually the negative lead and should go to the ground side of the 12V. If the ground is along the lower edge of the perf board, the capacitor's leads needs to be reversed.

Ken

 

Read the end that I added to my last post.

Ken

 

After reviewing the minimal white board layout, it looks like it should work OK. You might take it all apart and reassemble it. I have found bad connections on some of those that don't show up on visual inspections.

Ken

 

OK. I see a mistake on the white board. Top of the middle picture. The black water-detection wire should go to the junction of the 10K and 1M resistors, not to the top 47K resistor. The left end of the top 47K resistor so go to common (blue wires), not to the water-detection wire.

Ken

 

Dear Kmoffett,

that problem got solved thnks a lotcan u also help me in telling what will be the leakage current since we are putting 9.4uF capacitor at the input of pin 3 .how much leakage current is expected.can u also tell me possible causes of failure of this circuit in future.in short what are the shortcomings of this circuit

Why 9.4uF? Is that the measured value of a capacitor with a 10uF label? Leakage depends on the type and quality of capacitor used. What would be the significance of leakage for you in this circuit? The most likely component to fail over time in a harsh environment is an electrolytic capacitor. They could dry out and effectively loose their capacitance.

Ken

 

Dear KMoffett,

also If i want to reverse the logic with same IC that is water detected VCC(12V)-0.5V and with fuel 0.5V min to 1.8max can you tell me will this IC be sufficient if i do not connect my mosfet at the putput reversal of logic is possible but how much is the output current of LM311 IC alone.

Reversing pins 2 and 3 reverses the output logic. The pin 7 output is capable of sinking 50mA to ground.
http://www.national.com/ds/LM/LM111.pdf

Ken

 

its been our mini pjct automatic water level control

 

leakage current i need to know for the testing purpose.i am connecting two 4.7uF capacitor in parallel to meet my respective time delay.So i need to know how much value of leakage current can be expected how can i check the leakage current or how to calculate the same for this circuit.Kindly help

What are you testing in that circuit that the small leakage current through an electrolytic capacitor would effect?

Place a multi-range A/ma/uA meter in series with the capacitor's (-) lead and ground. Set the meter on the highest range. Place the circuit in the state that you want to quantify. Adjust the meter's range switch to lower and lower settings. Eventually you will read the capacitor's steady state leakage for the particular circuit state. Return the range switch to the highest setting before changing circuit conditions.

Ken

 

Dear Ken,

I know the maximum sink current which is possible is 50mA i want to increase the same current to 250mA without using mosfet .What changes i need to incorporate in my circuit to meet this new current requirement of 250mA.

The LM311 can't do 250mA without an external BJT, MOSFTET, or relay.

Ken

 

dear Krishananvsalim,

Are you designing on the same concept ?

actually we ve done it a long tym before,i ll try 2 get tat ckt and all

 

Dear KMOffett,
i connected the ammeter between capacitor negative lead and ground and kept the range of multimeter on maximum and kept my electrodes dipped in water the leakage current was not showing it was showing a value of 1mA only is this the leakage current ?since the capacitor negative lead is already grounded .

The ammeter has to be placed in series with the negative lead of the capacitor, so it measures the current through the capacitor, not in parallel withe the negative lead and ground. The way you have it now you are just measuring the current through R1 and the water, or just R1 if the electrodes are out of the water.

Ken

 

Can you post the PCB layout and associated schematic you used?

Ken

 

The time is a function of both R and C. With R5 at 220K, increase the value of C1/C2 by a factor of 3 or 4.

Is your PCB now working? What program are you using to create your PCB. I don't have time right now to create overlay transparencies from the PDFs to trace out your layout.

Ken

 

Sorry, don't have that. Perhaps someone else has it Orecad and can cross check your layout with your schematic.

Ken