Motion sensor using Pin Photodiode and LF353 and LM393

Thread Starter

Nickmar2877

Joined Dec 6, 2021
17
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.
View attachment 267386
View attachment 267389
Hi Sir Eric, thanks for the simulation, you're right when there's a motion, output voltage is 3.3V at the comparator of pull up resistor. Motion sensor changing the voltage at inverting input from 6.5 (no motion) and 1.5~2 V (with motion). For clarification sir, what is the purpose for 1N4148 diode to be in reverse position after the output of LF353?
 

Thread Starter

Nickmar2877

Joined Dec 6, 2021
17
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?
Yes sir, this is actual product with motion sensor. I think for the high value feedback resistors due to the target output voltage at LF353.
 

ericgibbs

Joined Jan 29, 2010
18,766
hi Bill,
If you look at the last image of post #15, it shows the Frequency versus Gain plot of the OPA's,
Note: how at 1k [my test Sine wave input], the Gain is down to ~ +10dB at 1kHz.

E
 

ericgibbs

Joined Jan 29, 2010
18,766
Hi Nick,
I believe the designer added the diode in order to allow only the Low going pulses from V(o2) to be connected into the Comparator input.
Do you have any information on the sensor you could post.?

E
 

Thread Starter

Nickmar2877

Joined Dec 6, 2021
17
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.
View attachment 267386
View attachment 267389View attachment 267390
Hi Sir Eric, can I have a copy for this ltspice simulation? Thanks.
 

Thread Starter

Nickmar2877

Joined Dec 6, 2021
17

Attachments

ericgibbs

Joined Jan 29, 2010
18,766
hi Nick,
The two LF353 OPA's in your circuit are standard type, connected as Non Inverting amplifiers.

The DC Gain figure for that type of amplifier is ...... 1+ (Rfeedback/Rinput).

So for Post #15 circuit.
DC Gain of first LF353 = 1+(2meg/205k) = 1+ 9.75 = 10.75

DC
Gain of second LF353 = 1(20meg/51.1k) = 1+391 = 392

Overall DC Gain = 10.75 * 392 = 4214

The Gain will fall as the frequency of the Input Signal increases, refer to the Bode type plot Post #15
Is this what you are asking.??

E
Added a PDF.
 

Attachments

Last edited:

Thread Starter

Nickmar2877

Joined Dec 6, 2021
17
hi Nick,
The two LF353 OPA's in your circuit are standard type, connected as Non Inverting amplifiers.

The DC Gain figure for that type of amplifier is ...... 1+ (Rfeedback/Rinput).

So for Post #15 circuit.
DC Gain of first LF353 = 1+(2meg/205k) = 1+ 9.75 = 10.75

DC
Gain of second LF353 = 1(20meg/51.1k) = 1+391 = 392

Overall DC Gain = 10.75 * 392 = 4214

The Gain will fall as the frequency of the Input Signal increases, refer to the Bode type plot Post #15
Is this what you are asking.??

E
Added a PDF.
Hi Sir Eric,

I'm asking the output voltage (Vo) calculation for lf353.
With non-inverting input varies from 6 V to 2.5 V (AC from sensor output) and inverting input 6V (DC supply) with 205K resistor going to the feedback.

Thanks.
 
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