Please help me resolve why the Output suddenly drops to zero

MrChips

Joined Oct 2, 2009
30,814
I graduated from the Bob Pease School of Hard Knocks.
I would believe the real circuit first before I trust a simulator.
 

Thread Starter

Vikram50517

Joined Jan 4, 2020
81
hi @ericgibbs i completely understand what you are trying to convey.
Also regarding Visible light reciever , you are right in that too!, ambient light F*s so much with my Reciever, such that i have to switch all those stuff off and then test my circuit . But can't the Problem be eliminated if we use a start and stop byte sequence before and after the transmission of data?

Also the IR tip is so cool
 

MrSalts

Joined Apr 2, 2020
2,767
Your simulator is not connected to power. The USB connector is not plugged in, there is nothing connected to 5+ And nothing connected to V(in). Try connecting your battery 9v+ to Vin on the Arduino Uno.
6D214C7C-7AB7-481F-B2FF-D14AC8679827.jpeg
 

crutschow

Joined Mar 14, 2008
34,453
@crutschow , just me testing stuff sir. I just wanted to see how a passive low pass filter works. That's the main reason iam testing this circuit
That's fine.
It just was not clear, exactly what the circuit was that you were testing, which makes it difficult to make an informed comment about what it might be doing.
 

MrSalts

Joined Apr 2, 2020
2,767
@crutschow , just me testing stuff sir. I just wanted to see how a passive low pass filter works. That's the main reason iam testing this circuit
First, your "schematic" in post 1 does not include an op amp but your image in post 13 does show an op amp. Which op amp is that? Also, what is the FULL circuit you are trying to represent - because somethings are obviously missing from the abbreviated attempt to communicate what you are doing used in Post 1. If you use a half-a$$ description of what you tried, and what failed, you'll get crap answers to clove your problem.
 

Thread Starter

Vikram50517

Joined Jan 4, 2020
81
@MrSalts True, the schematic that i posted actually was half a$$, i modified my circuit to include an op-amp at the end, so that i can see an amplified output. ( i used an IC741 op-amp). To describe by circuit in a single line its just a passive low pass R-C filter with the op-amp attached at the end to view an amplified output. That's the outcome i expect out of my circuit.

PS: I have not used a feedback resistor/capacitor on my op-amp, is that the reason why my circuit is messing up?
 

crutschow

Joined Mar 14, 2008
34,453
I have not used a feedback resistor/capacitor on my op-amp, is that the reason why my circuit is messing up?
Have no idea. My crystal ball is out for maintenance. :rolleyes:

Again, since you can't, or won't show us the complete circuit, we cannot make an informed comment about what it is doing.
 

MrSalts

Joined Apr 2, 2020
2,767
PS: I have not used a feedback resistor/capacitor on my op-amp
Well, with near infinite gain of an ideal op amp, and no feedback to control the gain, I'm thinking the output will be at max or min. Not a lotta filtering going on. 35 posts of useless crap - thanks for sharing the details of your circuit.
 

Thread Starter

Vikram50517

Joined Jan 4, 2020
81
I seriously don't know what information iam missing out and i definitely found the 35 posts useful in many ways. Allrigh, Anyways , i found out something is wrong with the tinkercad arduino simulator like iam messing something up in the simulator . let me make a last attempt in completely describing the circuit as succinct as possible. I tried out the below circuit in LTSPICE and i got an apt result and iam satisfied, the circuit works.

1647851245134.png

so the input is a square wave . the low pass filter has a cutoff frequency of around 1591 hz. the output is from an IC741 op-amp. all the values are clearly given in the schematic. The output still has a square shape to it but somewhat smoothened out, thereby signalling out that the filter is working!



I tried the same circuit with tinkercad arduino simulator, instead of Vinput in the circuit attached above, i used digital pin 12 of arduino as the Vinput. I connected the output of op-amp to pin A0 of arduino to read it. The result is its just printing continuous 0's . If i change the filter's R value to something stupid like 10000000 Mega ohm, the output spits out 5V dc constantly.

Iam happy that my circuit works out in LTspice, i dont know why it is not working in the arduino simulator. Anyways Thanks y'all for your interest and concern to clarify me .
 

AnalogKid

Joined Aug 1, 2013
11,052
No.

That circuit will not work in real life.

The power source is not referenced to the circuit GND. I'm surprised that LTS did anything.

A 741 will not run on a single 5 V power supply. The datasheet states the recommended operating voltage range.

The 741 is not a rail-to-rail component. Its input stage common mode voltage range does not include either power supply rail. IOW, the part will not perform as a linear amplifier if the input voltage is too large. Again, the datasheet lists the input voltage range limitations.

You don't state the output voltage amplitude you get in LTS, but whatever it is, it is not correct. Like the input (but for different reasons), the output voltage range has headroom requirements and cannot swing from rail to rail. IOW, with a 5 V power source you cannot get a 5 V output.

You have an input voltage of +5 V and a gain of -1000. Do you expect the output to be -5000 V?

As lowpass filter topologies go, that is not a good one. Better to change to a non-inverting amplifier such as a unity-gain voltage follower.

NOTE: Simulation programs do not simulate real life in ANY way. They demand that you keep all components within their operational limits, and will not tell you when they are not. If you change your schematic such that the 741 has to supply 1000 amps into a very low resistance load, LTS will happily simulate that circuit with no indication of any kind that a 741 cannot source 1000 amps.

I like LTSpice. I use LTSpice. But I never, ***ever*** trust LTSpice.

ak
 

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crutschow

Joined Mar 14, 2008
34,453
I seriously don't know what information iam missing out
Seriously?
You have a circuit that can't work in real life.
That's what was missing, and why verbal descriptions of a circuit seldom tell the whole story.
If the simulation does give you any result it's likely that the op amp is not doing anything, and the signal is just directly going through R2 to the output.
If you compare the output signal to the input it will probably be in-phase, whereas if the circuit were working properly it would be out-of-phase.
 
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crutschow

Joined Mar 14, 2008
34,453
. If you change your schematic such that the 741 has to supply 1000 amps into a very low resistance load, LTS will happily simulate that circuit with no indication of any kind that a 741 cannot source 1000 amps.
I think most 741 models do limit the output current to a more or less realistic value.
My 741 model in LT spice limits the short circuit output current to about 40mA.
 

Audioguru again

Joined Oct 21, 2019
6,693
The 741 opamp was designed to use a +15V AND -15V power supply. Its design is 54 years old!
It produces noise and its poor slew rate limits frequencies above only 9KHz.
Bury it.

The negative feedback of an inverting opamp causes the signal in its -input to be the same as the signal on its +input which is zero then your capacitor does not produce a lowpass filter.
 
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