I am trying to build a low pass filter circuit from the LM358 datasheet from TI. Looking at the pinout and building the circuit I cannot get something basic like this filter to work. I have everything connected properly, with the GND pin (pin4) connected to the negative power rail and the VCC pin (pin8) connected to the positive rail. I've been scratching my head over this the past couple hours, any help would be much appreciated.
You need to create a false mid-point for your amplifier. This can be done with two resistors and capacitors: -
Or, better still using an op-amp like this: -
Now, to make your input signal compatible, you'll need to feed it via a series capacitor like 10uF. This will remove the dc level from your input signal: -
If it is important to maintain the dc level then you have to use two power supplies with the centre point connected to ground.: -
Ignore the values, RL, Cp and RT - this is just an example.
As it stands, the op amp cannot handle any input below 0 volts, and about half of any AC input will be in this range, so it's no wonder the circuit doesn't work.
The lower op amp creates what is known as a pseudoground, and this is the reference point for the other two op amps. The pseudoground is commonly set halfway between the supply and ground in order to allow symmetrical voltage swings. The left-hand op amp is necessary to isolate the input DC level - without it the DC filter gain would saturate the filter unless you were very lucky.
Note that this loses your DC level on the input signal. As long as the input signal ground and the power ground are the same (and I expect this is true), this will generally be the case. There are ways to get around this, but I expect that this is a good start, given your apparent skill level. If you really do need to preserve DC, get familiar with this circuit, then ask another question.