Motion sensor using Pin Photodiode and LF353 and LM393

Thread Starter

Nickmar2877

Joined Dec 6, 2021
17
Hi to all

Good day.

Please help I got simulation error in multisim, this circuit is a motion sensor with op amp LF353 and I'm not sure if LF353 is used
as an Comparator or transimpedance amplifier

Thanks,
 

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MisterBill2

Joined Jan 23, 2018
11,876
neither stage is a comparator, nor are the component values reasonable. the feedback resistances are far too large, in addition to other problems.
 

MisterBill2

Joined Jan 23, 2018
11,876
Without knowing what the error message is I find it difficult to know which error you will need to correct. The circuit does have several rather obvious errors. It will not operate as shown in the drawing.
What do you want the simulation to show?
 

Thread Starter

Nickmar2877

Joined Dec 6, 2021
17
Without knowing what the error message is I find it difficult to know which error you will need to correct. The circuit does have several rather obvious errors. It will not operate as shown in the drawing.
What do you want the simulation to show?
Hi Sir, I had already pin point the error, incorrect pinning of the Op amp.
My problem is the function of LF353 in the circuit, kindly refer to the attached file for the whole circuit.

Thanks

Thanks
 

Attachments

MisterBill2

Joined Jan 23, 2018
11,876
The first LF353 is connected as a very high gain non-inverting op-amp. Both inputs are biased to about Vcc/2, about6 volts. It appears that the gain is about 1000. The second LF353 is connected for very high gain, with the 20 megohm feedback resistance. That may be intended to provide a time delay function. Again, the input bias voltage may not be correct. With no input signal the non-inverting input voltage and the inverting input voltage will be close, and so the output will also be close to zero.
The diode connected to the output assures that only voltages below 6 volts will affect the input to the LM393 comparator.
With such very high resistance values the circuit the simulator may have difficulties with the analysis process.

Using non-conventional symbols for the two amplifies stages and the comparator, as well as non-conventional input labels and a reversed signal flow direction do add to the effort required to evaluate the operation of the circuit. That may also have caused the simulator to have a problem with the simulation.
Direction and symols in electronic circuits are almost as important as spelling accuracy and writing direction are for this language that I am familiar with.
 

Thread Starter

Nickmar2877

Joined Dec 6, 2021
17
The first LF353 is connected as a very high gain non-inverting op-amp. Both inputs are biased to about Vcc/2, about6 volts. It appears that the gain is about 1000. The second LF353 is connected for very high gain, with the 20 megohm feedback resistance. That may be intended to provide a time delay function. Again, the input bias voltage may not be correct. With no input signal the non-inverting input voltage and the inverting input voltage will be close, and so the output will also be close to zero.
The diode connected to the output assures that only voltages below 6 volts will affect the input to the LM393 comparator.
With such very high resistance values the circuit the simulator may have difficulties with the analysis process.

Using non-conventional symbols for the two amplifies stages and the comparator, as well as non-conventional input labels and a reversed signal flow direction do add to the effort required to evaluate the operation of the circuit. That may also have caused the simulator to have a problem with the simulation.
Direction and symols in electronic circuits are almost as important as spelling accuracy and writing direction are for this language that I am familiar with.
Hi Sir, thank you very much for the inputs especially to the diode connected to the output at 2nd stage of LF353.
 

MisterBill2

Joined Jan 23, 2018
11,876
Now I still wonder about the source of this circuit. The selection of the very high value feedback resistors may lead to a problem of PCB surface leakage causing faults in an outside application. So is this an actual product or a proposed design?
 

MisterBill2

Joined Jan 23, 2018
11,876
The IR sensor for the circuit in post #10 is totally different from the sensor in the initial post.So the output from the sensor is totally different was well. An IR sensing diode produces a much smaller amplitude signal and has a much higher impedance. So the input circuit would be very different. I do agree that the second stage values are probably too high for practical use, although they may be OK for simulations that do not reflect reality.
And I am still waiting for te answer about the origin of the original circuit.
 

DickCappels

Joined Aug 21, 2008
8,704
Note: In the first two of the thread starter's schematics (posts #1 and #6) one of the inputs of the second amplifier is referenced to ground. The common mode range includes (in this circuit) 4 or more volts above ground. The common mode input range is something we should always check and be aware of. Not only do op amps stop working when this range is exceeded but some even invert sense, changing negative feedback to positive feedback.

Eric solved the problem - he used an op amp whose input includes all way down the ground and biased the inputs up above ground. That is safe.
 

ericgibbs

Joined Jan 29, 2010
15,509
hi Nick,
This is the result of a LTspice simulation, please check my circuit for any errors or omissions, etc.

What signal level do you expect at the sensor Input.?
E

BTW: I have redrawn the circuit to the usual configuration , from In to Out Left to Right.
[corrected 1000pF on input]

Added a 2nd sim with Negative going pulses at the input, Vout switches.
EG 1626.gif
EG 1627.gifEG 1628.gif
 
Last edited:

MisterBill2

Joined Jan 23, 2018
11,876
OK, so whst is needed now id to adjust the reference bias on the comparator The sine wave out shown in post #15 does not make much sense.
And thanks for the redraw, the circuit is now much easier to follow and analyze.
 

ericgibbs

Joined Jan 29, 2010
15,509
The sine wave out shown in post #15 does not make much sense.
It may not make sense to you, that's not it's purpose.

It was posted as demonstration for the Thread Starter, in order to show the overall response of the circuit output with an alternating signal.
 

ericgibbs

Joined Jan 29, 2010
15,509
OK, but getting a fair sine wave out of a comparator with no visible feedback is not common. At least not very common.
If you take the trouble to read the plots/labels on that particular simulation V(o2) you can clearly see that the sine wave plot, the plot of interest does NOT include the comparator section in the sine wave output plot.

There is no visible hysteresis feedback on the comparator because the original TS circuit does not show any feedback

Why do you insist on posting critical comments on 'helpers' circuits you don't understand and/or bother to read.?
 

MisterBill2

Joined Jan 23, 2018
11,876
Yhr fact is that indeed I did not read any of the fine print. Sorry about that. I would expect more gain with such large feedback resistor values.
 
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