LM 741CN Amplifier

[atntias]

Hi,
Im working on a project of mine and i have a small prob wich I hope you guys can help me with.

well, I have an output of +-5V wich is being changed constently and it can be + or - up to 5V, my goal is to amplify any value wich is outputed by 2.4 by using an external power supply.

Meaning, for example if +4V is outputed it needs to be 9.6 and if -4 is outputed it needs to be -9.6 when the extra V's are taken from external battery.

after some look up iv realzed i own a componted that fits the job wich is LM 741CN amplifier.

Thou the circute is supposly simple im having truble wich the schem if u guys can help me out il be greatfull.

Signed ThanksFull -Atntias

 

[Hero999]

So basically an amplifier with a gain of -2.4.

Is this coursework?

I don't plan on doing your work for you but I don't mind helping you.

A quick Google for op-amp inverting amplifier has revealed some helpful hints.

 

[evandude]

what you need is a standard non-inverting amplifier configuration.

**broken link removed**

That explains the basics... just choose resistor values to get a gain of 2.4 as you need.

bear in mind that you are going to have to power it with dual supply rails; if you need to be able to get an output of up to +/- 12v, then you should probably be powering it with +/- 15v. If you want to have batteries powering this amplifier, you'll need two batteries (or 2 sets of batteries) to get each the positive and negative supply voltage rails, which could be a lot of batteries (20 or so, if you're using AA's)

 

[atntias]

First thx so much and no its not curse work its just my privet project.

and yes i need to have +/- 12v but im already starting with 5V wouldnt that count?
i mean if i input the amplfyer +5v would he just add the other 7V (* 2.4) to make it a 12 or wuold it use the whle 12 from 1 place?!

 

[evandude]

no, it doesn't work that way. In a circuit like this, the input and output would be both referenced to the same ground, so the output of the opamp has to be able to swing to +12v for the specs you are looking for. The output can't "add" to the input voltage in the way you are thinking, because that would imply that the ground reference of the output was the input voltage, which it's not.

The idea with an opamp is that the input is basically just being MEASURED, and the output is coming solely from the opamp, from the power supply.

I wish I could think of a good analogy to make it easier to understand, but nothing good comes to mind, maybe someone else can think of something.

 

[atntias]

i think i underdtad but isnt there a way to do this maby other part will be better?

 

[evandude]

For the task of amplifying a +/-5v analog signal by a gain of 2.4, I think that a non-inverting opamp circuit is definitely the simplest and most straightforward way to do it, and is without question the way that I would approach it, provided there aren't any other important design considerations you haven't mentioned.

Since you are planning to use batteries (a floating power source) it might be possible to come up with some circuit that would do this kind of "addition" to the original input voltage that you seem to want, however I think it would be a pretty poor design with different grounds, and probably not a good idea for a beginner to tinker with, because it would almost certainly be more complex to build and debug than the incredibly simple non-inverting amplifier configuration.

Why are you so intent on this additive amplification you have in mind? Perhaps if you explained some more details of what you're trying to accomplish then we could provide some more insight.

 

[Hero999]

First thx so much and no its not curse work its just my privet project.

I certainly wouldn't help you with curse work since I don't think teaching people to swear is a good thing and I'm also afraid I can't help you with your privet project either since I'm no good at growing things.

 

[atntias]

Hero999 im sory if im not clear english isnt my first language.
as for the circute well this is the whole story:

I had a remote controled gas car, wich i just converted to dc motor (12v) and the reciver on the car can only output +/- 4.8v and 4.8V is bearly hinof to even make the motor start. basicly i need to multiply it by atleast 2.5 and it will be much better if it will be added b/c it lot of space and wight in the car.

I was thinking b/c the input voltage(+/- 4.8v) is not directly from the battery rather then going in reciver to servo controler and only then to ot put maby its possble to conect it to the reciver AND to the Vcc that way u dont need to add since it count as Vcc.

 

[Nigel Goodwin]

You've now COMPLETELY altered your original request, an opamp is completely unsuitable for this - and as you thought it was?, I doubt you are capable of building something to do this.

The receiver on the car should output a servo pulse?, which originally went to a servo that moved the throttle - this servo pulse now needs feeding to an ESC (Electronic Speed Controller). You need to buy this as suitable for your motor and battery - it's NOT something you're going to be able to build yourself!.

 

[evandude]

Wow, good thing I asked for details! yes, as nigel says, the signal you are getting from a receiver is not +/-4.8v, and it's not analog... it's a digital signal with a variable pulse width that controls a servo. This is EXACTLY what ESC's are made for. R/C electric motors can draw tens to hundreds of amps, they need to be driven by big, hefty power transistors in the proper manner, and building your own ESC is completely outside the realm of reality for a beginner at electronics; even if you could build one, it would cost you more money than simply buying one.

Again, your "additive" amplifier idea would be even LESS realistic in this situation... if you were trying to add to the 4.8v from the receiver, all the current for the motor would have to come from both the battery pack with which you power the motor, AND the receiver battery pack, which would cause the small cells in the receiver pack to immediately explode, for certain.

With most ESC's, you plug in a main (large) battery to the ESC, the ESC has a wire which supplies power to your receiver (which no longer requires its own battery), and has another wire that plugs into the receiver in place of the throttle servo that would have been in your gas model, and then of course the motor is connected to the ESC.

FYI, it would be a REALLY good idea for you to search around regarding the existing technology of electric R/C vehicles. Had you searched that, you would have realized that electrics still use the same kind of receivers as gas models, and use ESC's, not custom homemade amplifiers to drive the motor... Furthermore, with the kinds of high power that an electric is going to be using, you are going to need to do enough research that you know how to properly wire it up, with connectors and wire that are suitable for that amount of current, so you don't go blowing anything up. So, I would suggest you start searching and reading!

 

[Hero999]

Hero999 im sory if im not clear english isnt my first language.

I'm sorry for mocking you but please say so in your profile or else people won't make any allowances for you.

 

[Nigel Goodwin]

I'm sorry for mocking you but please say so in your profile or else people won't make any allowances for you.

However, YOU don't have your location entered either!

 

[Hero999]

Hypocritical I know, but I'm English so it doesn't matter, anyway I've fixed that now.

Hang on just a second, we shouldn't presume someone's first language is English just because they live in an English speaking area, perhapps we should have a separate box for first language.

 

[Nigel Goodwin]

but I'm English so it doesn't matter

The English technique!, just shout louder and louder till they understand!

Hang on just a second, we shouldn't presume someone's first language is English just because they live in an English speaking area, perhapps we should have a separate box for first language.

Not enough people even enter their location!, so I don't think it would help too much, but at least location gives a clue - and it's helpful for many other reasons as well.

 

[atntias]

First Hero999 I did live in the US for 2 years but moved back to Israel

As for the motor maby i didnt explain the hole thing correctly. b/c what i did is(wich i already done for my robot and is working great) i opened up the servo engine and took out the little motor and the gear and insted of the little motor i connected a diff. motor and that contorls its speed pretty well. this iv done for my little robot using a 3v motor and its working well for me.

i thought if il amplfy that maby it will work but in light of the fact of what i hear i think il just buy ESC.

im just a natrual improvilzer and i have bearly basic knowlge of elc. im still in school learing elc. this is my first year of elc and i like to get in over my head with things and i do blow-up/burn alot of thing but thats just my way to learn. yet i have some secssues (like this **broken link removed**
**broken link removed**

(wich is my robot pc control thats working great for me so far)

in any cae id like to say thx for the help and for the time i think in this case il just buy a proper componant.

THX -Atntias