I would like to build a copy of this circuit on a breadboard and have been trying to figure it out through these three images.

I used Falstad online circuit simulator with a voltage source of 5V and a 100mV test signal.

There's a capacitor connected between the VCC leg of the IC and somewhere else I cant figure out.

I was expecting a more prominent voltage swing when adjusting the potentiometers. There must be something wrong im overlooking as I dont know much about opamps.

Thank you

 

Hi FB,
Recheck pins , #5 & #6
Note = + & -
E
Update:
That 0V connection from the Non invert pin should also be removed.

 

that cannot work, second opamp inverting input is grounded, the non-inverting input is used to create positive feedback so output will always latch up. without access to the board and removing any parts, this seem to be the likely circuit:

 

Thank you so much for your corrections and for the schematic. Now the simulation seems to run correctly on Falstad: https://tinyurl.com/28o56qdz

I edited my image as I had also mislabeled a copper patch as VCC instead of GND. I attached the corrected image to this post.

 

I put the following project together around an LM324, the input signal coming from the magnet vibrating over the 150 ohm coil.

The plan in to rebuild it around the LM358. Any suggestions regarding some components I should add for signal condition? Like filtering, for example.

 

no schematics?

 

The old LM324 and LM358 use noisy (hiss) opamps that have trouble with frequencies above a few kHz and produce crossover distortion.

 

no schematics?

I want to turn ON and LED when a very small vibration of the magnet generates a current through the coil (a small voltage across its terminals).

https://tinyurl.com/28xvumsd

 

Hi,
You are showing P MOSFET, when Out=0V the MOS & LED will be On.
What is the type of MOSFET?
E

 

Hi,
You are showing P MOSFET, when Out=0V the MOS & LED will be On.
What is the type of MOSFET?
E

Replaced by an AO3400 n-channel logic level mosfet.

Should I add a zener diode to the non-inverting input of the first opamp to deal with possible voltage spikes?

 

Hi FB,
That combination of 1K and 100nF should remove any spikes.
What signal level do expect at the Input of the 1st OPA.?
E

 

Frankly I dont know, as I dont own an oscilloscope. I only measured the resistance of the coil with a multimeter, which is around 180ohm. ..

 

Hi FB,
Interested to hear how it works when you have built it.
E

 

the input to the circuit is AC... i would to get the steady output rather than pulse train.
probably use AC coupling, high gain, and missing pulse detection circuit (or rectification, filter...)

 

the input to the circuit is AC... i would to get the steady output rather than pulse train.
probably use AC coupling, high gain, and missing pulse detection circuit (or rectification, filter...)

I need to get an oscilloscope before attempting something like this

 

Hi FB,
Interested to hear how it works when you have built it.
E

Done and working adequately, thank you.

 

You already have DC pulses since the LM358 input rectifies the AC signal. Simply filter the DC pulses to make an average or peak DC voltage. It might take a fairly long time for the rectified DC to reach its maximum.
Note that your signal input is AC but the LM358 Absolute Maximum Input Level is -0.3V.

Wires all over the place on a breadboard usually pickup lots of AC from electricity and other interference since the wires are antennas.

 

small mod could do it too
https://tinyurl.com/2ygqecvx

added switch...