Voltage problem of resistors in a circuit

Hi,
I've an elementary problem: why I don't have 5V in out? ..measuring I obtain 3.84V with 12.45V from battery. I've mistaken the circuit?

(I'm in difficulty!)
Thank you!
Marco

Resistors

The voltage should be 12.45V * 604K / (845K + 604K) = 5.19V.

Measure the two resistors to be sure they are the correct value.

What voltage do you measure across the 845K resistor?

Maybe your volt meter has a relatively low input resistance, so it's drawing significant current from the circuit and decreasing the voltage.

Resistors

This voltage should be somewhere arrond 5v. But you have mention about that come aroung 3.82V. I think there is the problem that the resistor that you are placing maynot have proper value or its tolerance level is high. As you know that the resistace of your measuring voltmeter should be as high as possible. Theoritically it should be infinite. There may be the problem with your voltmeter too. Or there may be the problem due to the voltage rating of your capacitor that you have used across the resistor. Check the voltage rating of your 1 microfarad capacitor.
For getting the better result you can use the resistor with the high accuracy. For this you can use the ressistor with 5 color code. This is more accurate than the 4 color code. Second you can measure that voltage with different voltmeter so that you can say that where there is problem with your voltmeter or not.
Hope this will give you some idea for your project.

Re: Resistors

The resistances 73.2k+1k+100k+100k+100k+1k+5.6k+10k could be in parallel with the 604k resistance.... so that its effective resistance drops.... so you might be getting a low voltage than the expected value...

Re: Resistors

Pin 1 is floating?

Re: Resistors

I believe that the tester has one resistance such to create problems: 604K in parallel with 1M (of the tester)=376.5K and this in partition with 845K, with 12.45V of alimentation, supplies properly 3.84V!
I must to change tester!
The CIRCUIT is right therefore?
THANKS MANY, Marco

Re: Resistors

Raymond_di said:

Pin 1 is floating?

Click to expand...

Pin 1 has nothing to do with it...

Added after 1 minutes:

marcocoto said:

I believe that the tester has one resistance such to create problems: 604K in parallel with 1M (of the tester)=376.5K and this in partition with 845K, with 12.45V of alimentation, supplies properly 3.84V!
I must to change tester!
The CIRCUIT is right therefore?
THANKS MANY, Marco

Click to expand...

Yep, your circuit looks right, Marcocoto. Perhaps it is time to invest in a decent digital multimeter. They have become really cheap and affordable.

Added after 3 minutes:

marcocoto said:

Hi,
I've an elementary problem: why I don't have 5V in out? ..measuring I obtain 3.84V with 12.45V from battery. I've mistaken the circuit?

(I'm in difficulty!)
Thank you!
Marco

Click to expand...

Forgot to include in my previous message...

May I suggest to use a couple bypass capacitors over the powerlines (+/-) on IC1, and sensor input? 0.1uF type is good.

Resistors

Pin 1 it's the result of an wheatstone's bridge amplification.. near 5.25V; I need 5V to use them in a "offset" and measuring, between OUT1, 0.25V!
I'm happy that my "little circuit" work.. I think of change the value of the resistors in partition: 60.4k and 84.5K!
Bye!