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i read about virtual ground but still dont have clear idea how things connect each other.
can you please point me to some kind of "idiot's guide to opamp virtual ground" ?
Two resistors of say 2k2 each (for close to 1mA at a 5V supply), one from positive supply line and one from 0V.Join the free ends in what is your artificial ground.Use a cap of eg. 10µF (or whatever's handy) between this node and 0V.This will do for most circuits.BTW. It is sometimes called a supply splitter, if that helps getting a picture of it.If the artificial ground is loaded too much, it will start to sag in the direction of the load. In that case, a common voltage follower op amp is used as a buffer.If the ground is very capacitive, a resistor of ~100 Ohm on the output, with the feedback connected to the "outer" end of it will help.
Just to say if I were you I would go with a voltage divider - Darlington configuration... Ask Soeren to explain, I bet he would be happy... :-p
Generally, I mean something like the picture below, unfortunately their regulation isn't very good...You know there is a standard voltage drop between base and emitter, for a single transistor that's 0.7V, for a Darlington it's 1.4, cause is a double transistor, or a transistor in series.The bad thing is that their regulation heavily depends on the load...Anyhow, say you have a 12V voltage supply, how come you don't use a 7806??? That's simple enough.And there may be also 78L06 that's the low power equivalent that also comes in a "standard transistor" package... To - 92 if I remember right.Anyhow, there is also the LM317 that you can use.... Many many choices really ;-)Best Regards, LefterisGreece
I had the idea you were in need on a negative voltage with a single supply... right???
now i want to replace this op amp with TL081 which has null adjustment.so I thought to begin with TL082.
and in your diagram lets say i want to make non inverting amplifire with gain of 10 how can i modify the circuit?
Quote from: TrickyNekro on April 04, 2011, 07:34:36 AMI had the idea you were in need on a negative voltage with a single supply... right??? ya sort of but i dont see how you get negative supply from darlington couple or 7806
And here is the circuit, [...]
The gain in your schematic is 11 (R1/R2+1).Did you measure the capacity of X1?If it's more than 10nF, increase the value of C1 to at least 10 times (up to say 100 times) the capacity of X1.Add a resistor of 910R (R1//R2) between C1 and pin 3 to match the impedance of each input. Even better, use a slightly larger resistor and make a (high impedance) splitter to keep the non-inverting input in check.I can't imagined what you're trying to do with an LED on the output, but perhaps it's just for visual confirmation or something along that line.When you make the artificial ground, then, when there's no input from X1, the inputs of the op-amp will come to rest at Vcc/2 and so will the output. Your amplified signal will thus be symmetrical around Vcc/2.Lifting the ground side of the LED to Vcc/2 as well would keep it off with no input and (with luck) flicker weakly at 40kHz if the input is very strong. But then you'd need the buffer on the splitter.Two CR2032 coin cells could be used to make a +/-3V supply.
And here is the circuit, the ground is the Ground for your microprocessor etc etc etc...If 9V regulated is a must, then you should immigrate to 3V - 3.3V logic...Just a note though... Should you use this circuit, then you must find out about precise rectification methods,(NOTE: That's basically some Schottky diodes with some op-amps, one or two, depending whether you need half or full wave rectification) as this circuit will give you negative voltages, that a microprocessor can NOT handle at its inputs...Peace out,Lefteris, Greece
I measured the capacitance and its around 2nF.
LED is for visual confirmation.I'm planning to feed the output of the op amp to LM567 tone decoder.
lets say I use a single supply op amp for this circuit. then how should i connect ultrasonic receiver unit to the op amp input?
is it correct to connect one pin of the transducer to op amp non inverting pin and other to the ground (0V) supply rail (in single supply) as in my circuit I posted above?or should i connect one pin of transducer to non inverting input and other to a voltage divider as you mentioned above?
I have a feeling that if I connect one pin to a 0V supply rail it will cut off negative part of incoming signal and will reduce the sensitivity.
OK, but what's the purpose of the '567?If you want to measure distance, you want as little delay in getting the return pulse (or pulse train) back into the controller. If you use a '567, you'll get a delay with a magnitude depending on the quality of the signal (the lock time).
With the 100nF capacitor, you could use a voltage divider (with high value resistors) on the non inverting pin instead, as the cap will "remove the ground reference".I'd use the voltage divider (with a cap) for the "ground pin" of te transducer however, as you then won't need to lower the input impedance of the op-amp.
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