uA741 won't work well from a 5V supply. The input and output voltage ranges for a typical part would be 2-3V and 2-4V, respectively.

A worst case part wouldn't work.

 

If you dont understand something, just tell me and I'll clarify it for you.

Haven't followed for awhile but what is the purpose of the op amp circuit?

 

I'll answer both @dl324 and @sghioto
Thank you for your reply. You are right and i already know. The idea is to get a little bit of functionality from the opamp. Im not interested to use it rail to rail. That little bit can drive a transistor that will do the rail to rail thing... i imagine. But im a bit new to opams, and my experience is very limited, but i push with what i know so far. Thats why i come to ask your help. So make me or give me an idea about using it to amplify that very small signal, that is all the point to it.

 

The good part with the [ldr with opamp circuit] is that the LED is completly turned off and on ! So the opamp circuit is fine. What is not fine is my lazy signal. Thats why the same led is just dimming when I put my signal. Should I make you sketch with what i just said here? Its no problem, I want it to be very clear. So I can forsee a silverlining but i dont know how to make it yet. I hope you get me now.

 

Should I make you sketch with what i just said here?

Yes

 

If you want me clarify it some more, tell me.

 

The circuit is not an amplifier it's a comparator. If the voltage on pin3 is higher then pin2 the output will be high.
This is the case with the PC817 if the internal IR LED is not activated which explains why the LED is always on.
What are you trying to achieve with the PC817?

 

I'm thinking that the relay is trembling because the transistor switching it isn't being driven hard enough. Try this to see if it helps:

It will give you more current gain and a higher voltage on the base of Q2. This is a split Darlington configuration and doesn't have the problem with a saturation voltage 0.7V higher than normal.

 

The circuit is not an amplifier it's a comparator.

That's what he wants. He wants the relay and its LED to be turned on when the 10th LED is on.

 

What are you trying to achieve with the PC817?

From the last pin of lm3914, when is activated, I want to transmit a signal to the relay. The PC817 is just another led in the row, and is picking up when this last pin is activated. Basically. But for some reason, the signal to this last led is too weak. And it reflects in the relay, trembling, vibrating. Most probably the led is fluctuating as well. I can see the other visible leds are fluctuating so for sure the led inside PC817 is doing the same.

 

Of course the input of the opto-coupler is an LED. It is shown on its datasheet, and its sensitivity code marked on it.
The 741 opamp was designed 53 years ago to use a 30V supply as shown on its datasheet so many of them do not work when the supply is only 5V.

On the LM3914 the resistance to ground on its pin 7 sets its output currents.

 

That's what he wants. He wants the relay and its LED to be turned on when the 10th LED is on.

OK I get it now.

Most probably the led is fluctuating as well. I can see the other visible leds are fluctuating so for sure the led inside PC817 is doing the same.

That's the problem. Just need to figure out why the LEDs are flickering or add some capacitors to the relay circuit.

 

I just made the repair of my previous mistake.
I put the led of the optocup PC817 in paralel, like the rest. (it was in series)
I also eliminate the last red burned leds laying around, in the idea, maybe some weird leakage may occur through them and influence the sensitivity. It may have been ! Now when I tested it, it got more brighter than before.
BUT... when I attach the optocup PC817 led, the last leds on pin 10, dont turn on. Very weird. Now that you mention is a IR led inside, maybe it has other requirements than the last red red.
I also colored in my sketch here, that the rest of 9 leds are blue, and the last 10th is red. Im mentioning this because red led has different voltage to operate than the blues and also than the IR led.
I'll have to measure what is going on there, I only look and tell so far. This circuit is cursed. Or I am.
Here is what I just did so far:

Mister dl324, I have already a relay driver that uses this circuit:

I will try your circuit that you made now as well, but in continuation of the ones I have already installed. Because it's all glued in there. I will also try it with a separate relay, just for tests. So I will try it in 2 ways, is all im saying.

 

That's the problem. Just need to figure out why the LEDs are flickering or add some capacitors to the relay circuit.

Please consult this full circuit to clarify yourself:
https://www.deviantart.com/q12a/art/Q20201219-Led-Wings-Projekt-Circuit-864540519
zoom in it, its at it's best rezolution there.
I am using a sensing circuit. And that is the principal factor of turbulence in the leds functionality. All I can concentrate now is forward, after the leds.

 

Now that you mention is a IR led inside, maybe it has other requirements than the last red red.

It does. The voltage drop across an IR diode is typically 1.3 volts. If you put this in parallel with the red LED the IR diode will basically short it out. You could try adding a resistor in series with the opto LED , try 100 ohms.

 

Leave the LED in the optocoupler in series with the 10th LED. The 3914 drives the LEDS with current sources. If it runs out of headroom, the 10th LED will just be dimmer than the rest.

 

It does. The voltage drop across an IR diode is typically 1.3 volts. If you put this in parallel with the red LED the IR diode will basically short it out. You could try adding a resistor in series with the opto LED , try 100 ohms.

Excellent answer. Though I did the try before reading your answer, but your answer totally confirms it. I did test with 1k and then with 10k. The red led is bright now. So that problem is solved. Oau. Phiu.
I made a tiny modification to the PC817 output; I linked it to the +5V and to the S (Signal) to the relays.
I've also updated it with the salvation resistor.

Though I observed an interesting thing. When I put 1k and if I'm putting my multimeter probes to the output of the PC817, the relay trembles incontrolable. But If I put 10k, and the probes, it does not tremble anymore. But still not working either. I think it might be a clue there, in that behaviour. Hmmm.

 

Leave the LED in the optocoupler in series with the 10th LED. The 3914 drives the LEDS with current sources. If it runs out of headroom, the 10th LED will just be dimmer than the rest.

If it didnt work out, I was also planning to revert it to the working stage from before. Now is better ! We have 2 problems now that remains to be solved.
1- trembling bypas ( I imagined with an opamp in the begining)
2-amplifying from this stage I am right now.
The emitor - colector of PC817, (it's output), it stays at 4V when nothing is activated, and gets down to 3V when the last red led is activated. Now is waaay much better voltage diference than before. Now is 1V and before was 300mV(when in series). This is progress, not much but an important one.
Added more text here:
Oh, the relay has 1.5V diference of actioning. I just test it with my Power Supply at 1.5V it gets off and at 3V is on. It stays off OR on in between 1.5 and 3 until it gets over those values.

 

Try this modified version of the circuit Dennis posted in #168.

 

Another version controlled directly by Pin #10.