I have problem with an lm386 op amp in an non-inverting configuration. For the resistors, I take two equal resistors so i set a gain of 2. When i put a signal of 3.3 volts on the non-inverting pin, i should get 6.6 volts on the output on the op amp, but i get totaly different measuring. I have also measured the voltage on the inverting and non-inverting pins and i do not get the same voltage but i should. Also when no voltage is connected on the non-inverting pin (when its grounded) i am not getting 0 volts on the output, but i am getting zero point something volts. I have also tried to change the ic or the resistors but it didnt worked. So now i wanted to ask am i makeing a mistake or the mistake is in the ic. Every answer is welcome. Thanks a lot.
Electronic – Non-inverting op amp problem
lm386non-inverting
Related Solutions
I sample 4 times per second and I repeat it for about 20 cycles for smoothing of values using moving average.
OK this is the basic information needed. To prevent the effects of noise causing aliasing you need to filter the signal before it enters the ADC at below 2 Hz. This might be best done on the final op-amp (gain stage) by using a sallen key filter: -
This is a typical circuit although the values will be different for your application. Here's the link for the circuit above - it may be useful for you. Here is a very useful link - it's a calculator and this is what the calculator looks like when you scroll down the link to the relevant part: -
You might also consider putting a capacitor across the lower of the two 10k resistors that feed the 1st AD822 - a value of 33uF creates another 1Hz low pass filter that, along with the sallen key filter gives you a third order filter. Even so, depending on the noise this may not be good enough and a final rC filter on the output of the op-amp stage converted to a sallen key filter may be needed. 10kohms and 10uF would be about right.
And, if all this seems a little over-the-top, consider sampling at a much higher rate (maybe 100 times per second) because the filters require smaller capacitors and you can average more in your MCU.
One final thought - the IA may be subject to EM Interference and this may require 1k ohms in each input leg with a 100nF across the two input pins.
You need to ensure that the inputs of the 741 (any op-amp, in fact) are within the input common mode range. On the 741, that range is within 3V of each supply rail, according to the datasheet. The output also cannot swing all the way to either supply rail.
If you use supplies of +/-15V (the common must be grounded) then the circuit should work, however you show only a single power supply of +30V with no ground reference. If it is, in fact, floating as you show the circuit will not work, and it will not work if either side of the 30V supply is grounded. You also cannot use a voltage divider because current flows to the ground through R1. You could use another op-amp connected as a unity-gain buffer and a pair of equal value resistors (eg. 10K each) as a 'rail splitter'.
simulate this circuit – Schematic created using CircuitLab
Or swap the ancient LM741 out for half an LM358 and ground the (-) of the 30V supply and things will be okay (for positive inputs only).
Best Answer
Whenever you see a big difference between inverting and non-inverting terminals, one of three things may be happening:
LM386 is an audio amplifier, not an op amp, even though it has some superficial similarity.
According to LM386 datasheet, the open-loop gain
Avis only 26dB i.e. 20V/V. This is far from the ideal opamp where Av is considered near infinite.Consequence of this reduced open-loop gain is that there will be significant difference between the inverting and non-inverting inputs, as you observed.