Can someone checkout the attached circuit for me (amplifier)?

Projects General Guidance
1

The link attached is the circuit which I constructed and tried simulating. I spent hours with it but the simulation doesn't give me the result I want. Can someone check it out and correct it for me if theres any mistake. Its a circuit to filter frequency and then amplifies the voltage to pass to arduino ADC. Basically it has 4 stages, which are:

stage 1: Band pass filter to get frequencies from 700 Hz to 2000 Hz.
stage 2: Amplification with a gain of 14
stage 3: Amplification with a gain of 14
stage 4: Diode to cut off anything above 5V

Circuit Link:Complete Circuit

So, can someone please simulate and correct the mistake for me if there is?
Thanks

2

I don't have a simulator application -

120 volts into an op-amp circuit looks dangerous to the op-amp, your Arduino, and to YOU! The common practice is to use a transformer or opto-isolator between the line voltage and the circuit.

Does your simulator tell you how much power dissipation you've got in the capacitors & resistors connected to the 120V input? I'm thinking everything is going to burn up! :frowning:

You've got 1 Ohm resistors in series with 47uF. I assume that should be 1k Ohm? Perhaps with a smaller capacitor?

My "gut feeling" is that you are going to have trouble filtering-out the 120V 60Hz signal while amplifying the 700-2khz signal by ~200 (14x14). You'd need a very steep (high order) filter.

3

Is the arrangement of both high pass and low pass correct with bias voltage divider? When calculating the high pass filter should I take the total resistance of the parallel 113 ohms or just the one connected to ground?

The circuit is corrected, actually the input is aroudn 23mV Vpp. So, can I filter using the arrangement?

Thanks

4

@yaantey

I look at the circuit, you right, it need to re-design in my opinion... I will try to help you, ( I have two simulator ) A free simulator from http://www.linear.com It base on Spice, you can simulate with that circuit, but the software and to use it is a bit "technical". But It can calculate pretty good.

First, I want to know a few details of what you want the circuit to do...

  1. Minimum signal in
  2. Filter frequency
  3. What output you expect.
5

? When calculating the high pass filter should I take the total resistance of the parallel 113 ohms or just the one connected to ground?

Parallel, 56.5 OHm., HPF : freq. = 1 / 2xPIxC2xR1||R2 (56.5) = 1409
LPF, freq. = 1 / 2xPIxC1xR3 = 2041
Two HPF: freq. = 1 / 2xPIxC3(or C4)x R5(or R7) = 3.38

6
  1. Minimum signal in
  2. Filter frequency
  3. What output you expect.
  1. 23mV Vpp
  2. Bandpass filter: 700Hz to 2000Hz
  3. Sine wave, biased at 2.5V with maximum V = 4.5 or something like that and minimum V = 0 or something like that.
7

Thank you yaantey. Did you download the sim from Linear ? It may help in your design.

8

@yaantey

I just finish a circuit that do according to your spec. It is just a "prototype", and need to be refine to get the frequency and output. I test using LTspice and check the frequency response, I have around 1.5 kHz ( top of the bell curve ) which in my opinion OK for now. I would like to share with you, but the upload and PM may still not working.