Led display Digital Voltmeter question

[Gruber]

thanks MP !
I saw this schematic :

it is different than the 2 ones on projects section.
But i have some other questions popuped since i saw the fixed circuit.
pins 32 and 35 are connected to the analog(common) ground,but in the other two schematics they are not,can this be considered as a mistake (for eventual problems)?
Also pin30,the "low" in is connected to the common ground too - another difference with the other two projects.This is the biggest "confusion" for the scheme - seems strange to connect the monitored voltage to the scheme.

I will remake the scheme,i hope those changes can help to run the voltmeter

 

[MP1]

This just assures your reference voltage, ground on the chip, and ground on the input are all at the same zero potential in this design.

Attached to this post are the original eagle files. You can get a free copy of EagleCAD in our download section. The attached zip file will give you the schematic and the board layout.

MP

ICL7106-7_Eagle_Files.zip

 

[Gruber]

thanks MP.
But still one question remains - can i use the ampermeter to measure the current of the power supply,which is powering the ampermeter ? sounds little confusing - but the case is : if i have a stable 5V 1A+ power supply can i power the ampermeter from it and use the ampermeter to measure the current fomr that 5V 1A+ line from the power supply ?

 

[MP1]

I am not sure what you are working with. The amp meter should be connected in series with the varying input voltage to the digital voltmeter. Does it need additional power? How did you intend to connect it? You should not power it with the varying voltage. If it needs to be powered, you should use the same supply that you power the digital voltmeter with.
MP

 

[Gruber]

there is the schematic of the circuit i am asking about.
is it possible to do it like this ?


sorry for the low quality image

 

[MP1]

I did not mean to give you such a generic answer. It will depend on the specs of your amp meters. Check what is allowed for power requirement to operate the meter vs input volt/current ratings. I doubt there is a problem with the one on the 5 volt source, but the one on the 30 volt source might need more voltage to accept a higher input such as this. This information should be in the data sheet that came with the amp meters.

MP

 

[audioguru2]

Hi Gruber,
I think our digital meter project cannot measure its own supply, so the A-meter for the 5V supply will need a separate supply.

When you have both a V-meter and an A-meter for a supply, the V-meter should indicate the voltage at the load, because the resistance of the A-meter will cause the voltage at the load to drop.

View attachment 37893

 

[Gruber]

hi again.
Thanks for fixing audioguru.I didnt get any atentioned about V-A or A-V connecting of the meters,i planed to do when eventually connect them in final PSU.

Can  i use this "circuit" instead of previous one ?

 

[audioguru2]

Hi Gruber,
I think the 12V and 5V supplies are too closely related to work. I think this digital meter project needs a supply that is completely separate from what it is measuring.

 

[MP1]

Normally you cannot use what you are measuring as the power supply to the device that is doing the measuring. Is this what you are attempting? Unless your device specifiically says it will do this, it will not. I am pretty sure this was addressed in one or more of the previous posts in this thread.
Your data sheets for the meters will tell you what is possible. Again, I point you in the direction of the data sheet for your device.

MP

 

[Bits n Bytes]

Hi MP,

 

[MP1]

Bits, you only need to limit the input. Obviously, you do not want to apply this much voltage to the input. This can be done in many ways. One way is to use a 10:1 transformer, discrete parts, and a little calculation. Is this what you mean by "current transformer"?
Once you have the correct stepped down ratio, you can use the diagrams earlier in this thread to provide current and voltage monitoring.

MP

 

[oxyll]

Hello guys , i was wondering , maybe someone build this project for reading car battery volts ? is there any way to make this cicrcuit work with supply of car battery and measure it ?

Thx

 

[Master-Dexter]

Helo everyone!!!!!!
I build this voltmeter a year ago!I use it for few measuements to test it and it was ok!I didn`t need it until i build a power supply!!!!
So i find my voltmeter to combinate it with my power supply!But, my voltmeter don`t want to work correctly!When i put any voltage on it`s input it start to oscilate!
So if i put 5 V on Led display i will se 5.09,5.04,5.00,4.98,5.05......It change value from second to second and it can`t stabilize it self.
For power it i use only positive supply +5V, but this can`t be a problem because it`s work just fine with +5V a year ago.
I had  thought that i maybe burn the IC with static charge or wrong polarity but everything else work fine so i don`t think so.
Any idea what it is wrong?????? ??? ??? ??? ??? ??? ??? ???
Sorry for bad english!!!!!

 

[MP1]

Did you add the power supply bypass caps? I cannot think of a reason why it would work a year ago but now with no changes it does not work. Something must be different.
Are you measuring a true DC waveform? Does the display agree with the voltage that is being measured? Please tell us more about your circuit, any changes to the original design and a little about the voltage you are measuring.

MP

 

[ante1]

Hi Master,

Are you trying to measure the 5V from the same source as supplies the power to the meter?

 

[Master-Dexter]

I didn`t mesure the voltage from supply that i powers voltmeter this is imposible to do because this chip need a referent voltage for mesure so if you take same voltage for power supply and for measurement the IC wouldn`t have anything to compare!

I can measure any voltage some stabilized power supply like this one on this forum os some other.I try to measure a voltage on stabilized power supply, on 7805, on1.5V, 9V battery and there is always same result, value is oscilating.It`s displays almost the corect value but it wont to stop to oscilate.

I beleve that same of the components are damaged or they just don`t work fine! :-\

 

[chiquitronic]

I MP,

i tried to build  the voltmeter, but dont work,  my voltmeter don`t want to work correctly!When i put any voltage on it`s input it start to oscilate!
So if i put 5 V on Led display i will se 3.09,2.04,1.56,1.35, .It change value from second to second and it can`t stabilize it self. can you help me , For power it i use positive supply +5V and -5 it ok, but dont work, wy???

thanks,
and excuse me my bad english.

 

[MP1]

Which project did you build? Can you post a link? There are two different projects. One does not show the needed bypass capacitors for the voltage supply.
What are you using for a 5 volt source? This device depends upon a filtered voltage supply. Especially the reference voltage.
Also, if you could post your schematic diagram if it differs from the original, this would be helpful. Did you make any changes to the original parts list?

MP

 

[DMITRY GOLOVIN]

is there anyone tested this circuit with a frequecny-voltage converter LM2917?