I've answered your last post with a picture:

(click on image to magnify it, then Right click on it and choose "view image" to fully load it at its original rezolution and be able to read all the little text is there)
Im a beginer with opamps so I may do some terible mistakes with them until i learn them good enough.
I already get a good idea about them, but is just teory at the moment. Ill have to get practical experience with them to be more confident. At the moment im using my best intuition.

 

Your new schematic has R1 and R2 providing an unregulated input voltage for the opamp.
My idea has the LM3914 pin7 providing a regulated input voltage for the opamp.

Look at the datasheet for the old 741 opamp. Every spec has a +15V and -15V supply! Your circuit has only +5V which is too low for it and does not even have a negative supply.
A LM358 dual opamp works perfectly with a 5V supply and does not need a negative supply.

I am just guessing (I said for you to try it) that pin7 of the LM3914 still works when it has a tiny load current so that the LEDs are dimmed.

 

Well, i did my best with what i have. I will buy LM358 when i will make some money and after that, wait for it to come in about2-3 months from china. So not very soon. But i retain what you told me and show me.
So... this experiment is concluded now? We got away too much with this because I also was somewhat interested.
Can we look over my initial problem(s) from this thread, please ?
If you have any interesting points, then lay it down here.
Thank you mister @Audioguru again .
And also mister @sghioto , did you thought on a way to create a sphere of "something", to enlarge the sensitivity for pin5 of the vumeter ?

 

Open this image first:
(this image is HiDef and you can read the smallest text in it, but you must open it properly, either download it, or in browser 1click to enlarge it and then rightclick on it and choose "view image")
View attachment 215289
I have 3 important problems to resolve:
probl 1: (!!!!!Very important!!!!!)
The area of the light is too small and the LM3914 circuit will create an On/OFF state for all leds, when interupting the beam. It will interupt suddenly.
Its not the circuit fault but exclusivly the light and LDR fault. Their dimentions are too narow and my finger is too wide for the circuit to sense it slowly. I need a way of enlarging the LDR surface that will allow penumbra to play its role on the lm3914 circuit and the leds to behave corectly. I have to evectively get into the beam light and interupt it right now, so it is no room for penumbra to leave the sensor to sense anything. Its too fast for the ldr to be able to cath other little diferences in shadow, other penumbras diferences. I need to enlarge the shadow area of the LDR. I dont know how to say it better than this. The shadow area right now is 0.5cm (or 5mm) (or 1/5 of 1 inch)
I wish I can enlarge the shadow area to about 5cm (or 2 inch) around LDR sensing area. When this area is so large, the ldr have the time and space to dim the leds 1 by 1 more elegant. Right now is too abrupt, too brutal, too fast, too narrow. You get me? If not, ask me, and ill add more details on this matter and drawings if needed.

probl 2: (not very important at the moment, is working as it is)
The new Laser diode, I inserted for the very large distance i can separate the triger elements. But, the Laser is too dim at 3V and im afraid to push it over 3V ( i can, i test it already and is brighter) but it will overheat and burn in a short period of functionality. Im not very sure how stable will be as it is at it's normal parameters.
My thought is to amplify the LDR signal to pin 5 trough a transistor because of this small laser signal. It is good light right now and working ok but not very bright and leaves other external lights to interfere. Of course ill have to make a new case for the ldr to defend it from external lights and concentrate only my beam on it.

probl 3: (important, but it can wait until the end)
All this trigger part, (laser diode + ldr module to pin 5) will have to be integrated with another pre-existing circuit. I'll have to change ldr module to that one, and adapt this one to do a double function: to action on pin 5 as it is now, and also to triger a relay from the other circuit. What a complication. I hope i can split the signal in 2, one for the pin4 and other for a transistor that will drive the relay. Ill have to test it and keep you in touch.

Here are the 2 circuits i must combine:
Light switch: https://www.deviantart.com/q12a/art/dBenzin100-ziuc-12a-Mains-Beam-Light-Switch-Latch-848347670
Vumeter with 3914 and LDR : https://www.deviantart.com/q12a/art/dBenzin100-ziud-20-Vumeter-with-3914-and-LDR-852598799

Hello,

Just a note...

It is better to download your pictures and then upload them to this forum so that they are stored on the same server. What happens if you link a pic instead is that something happens to the website you linked to and then nobody can see the drawings.
A Mod may say something to you about this.

 

It is better to download your pictures and then upload them to this forum so that they are stored on the same server. What happens if you link a pic instead is that something happens to the website you linked to and then nobody can see the drawings.
A Mod may say something to you about this.

I understand, but my way, redirecting to my portfolio artpages, will make my account visible to you and others, and can browse to see other works i did, not only the circuits i build. But as you observed already, I did uploaded only here for a couple of times also, because they are not something final, but in working stage. When is final, I will post it and link it as being something oficial. This is how i think. So partial progress is directly uploaded here, while final work/finished schematic is there and linked here. Is not that wrong in this way im doing it. I also experimented and find the best way in time. Thank you for your intervention.

 

I will buy LM358 when i will make some money and after that, wait for it to come in about2-3 months from china.

Money? Months for shipping? China?
The LM358 is made by Texas Instruments. Western electronic parts distributors have thousands of them.
One costs $0.36 at Digikey and they can deliver it to you tomorrow.
Don't buy cheap Chinese fakes.

 

In case anyone wondered, here is the datasheet for the dot-bar driver:

https://www.ti.com/lit/ds/symlink/lm3914.pdf

 

@BobaMosfet we already discuss about this datasheet, this is a continuation of older discuttions.

 

@BobaMosfet we already discuss about this datasheet, this is a continuation of older discuttions.

thx

 

This is what i need at this moment and if we resolve it, the project is finished.

where:
PERETE = wall
Area de efect = area of effect
Senzor = Sensor (of any kind, i dont mind).
20cm = 7.8 inch.
How can I implement it in these parameters ?
Thank you.

 

How can I implement it in these parameters ?

Does the sensor have to be that big? There are a lot of smaller size solar cells (50 to 100mm) that should work.
SG

 

Does the sensor have to be that big? There are a lot of smaller size solar cells (50 to 100mm) that should work.

I am not that precise in my drawing here, i forgot to mention. I am only focusing on the idea itself and the range.
I didnt give that sensor any size. I did specified, it can be anything, any type of sensor.
Your idea is good, but i dont have this solar cell, and it takes 3-6 months (IF) it will arrive.
Thank you.

 

3-6 months

Good Lord! Give me your address I'll mail you one.

 

Solar garden lights are sold at low cost in many stores with various sizes of solar panels. But most panels are square, not round.

 

A friend of mine, suggested a FET (field effect transistor) to use as my proximity sensor. It is a very old idea, back in the 80's electronic magazines. I played with them back then as well. I remember they didnt do exactly the thing i had in mind, but in general, they did had good range and somewhat usability, for this type of sensing circuits im into.
Back then I used BF245 or BF256 as a sensor.
My question now, they are still the same or they changed their names or they got better, more stable than the older ones?
What are the new ones names? I searched for them myself but im not sure i found the right ones. I think I find something else, and im afraid they are not the same or better than the old ones. Thats why i come to you to ask about them.
Oh... maybe there are IC now that are doing this sensing thing better.
I find 2N3819 as another type on ebay. I searched for [ 10pcs RF VHF UHF jfet ] or [10pcs RF/VHF/UHF]. Over 10pcs they get quite expensive.
I hope im searching the right ones. Dont lough on me, because im not used with these types of transistors in normal circuits. I never used one other than sensing.
Thank you.

Im also planning to make a mini antenna amplification. Hopefully, I will get this 20cm range with it. This part im not that good in it. But i know is working to some range. The transistors used here are BJT NPN General Purpose Transistor small power, like bc107 for example. Im also wondering if I can amplify this type of small signal through an opamp like my ua741 that i already have. I will have to test it, but maybe i can get some interesting feedback from you.

 

https://www.instructables.com/id/Pr...ity Sensor,relay, power transistor or mosfet .
SG

 

like bc107 for example and opamp like my ua741.

Wow q12x are all your components from the sixties?
SG

 

Wow q12x are all your components from the sixties?
SG

yes they are old Some i even bought ! haha
Thank you for the link and the video inside, its realy what i wanted ! Thank you!
I'm reading about this (new transistor for me) 2N7000 here : https://en.wikipedia.org/wiki/2N7000 and I see there is another SMD brother mentioned 2N7002 , but they mention they have some differences. I would listen to your original circuit and get 2N7000 but ... the SMD is attractive as well, what is your advice on it? Its the same thing? I think the TO92 package is "more" sensitive also because of it's long legs... but... internally should be the same. Im a bit in doubt right now. You really have been a great help, mister @sghioto .

 

what is your advice on it? Its the same thing? I think the TO92 package is "more" sensitive also because of it's long legs... but... internally should be the same.

The 2N7000 is a little more rugged in my opinion and if I was doing this that's the one I would use. However if you are going to order parts might as well get both.
SG

 

Thank you mister @sghioto , i buy them both.
I understand they are very susceptible to static electricity and very sensitive when handling.
Im wondering what are they most used for, in general? (beside sensing) Now that i have a good lot of them....