Led display Digital Voltmeter question

[noorussaad85]

Hi dude,
I have created the exact model as shown by ur schematic on the PCB.
But the only problem i'm facing is while measuring the voltage.
For example ............it displays a value of 1.4V for 1V input.......
14.1V for a 10V input........
28.2V for a 20V input......and so on
Basically the original factor gets multiplied by a factor of root 2 and then its displayed........
i checked it for a no. of values........but the problem prevails.......

try to get me a solution..........as soon as possible........

--Noorussaad.

[MP]

Did you use the modified circuit or the original which had some errors?
How is your reference voltage? Have you included all of the capacitors or deleted some thought to be unnecessary? Others have reported excellent results, so you will have to take a close look at what you have put together.

MP

[Gruber]

Hi.
i have several questions about the voltmeter.
I built it,but it has some problems.

1.When the input is empty,i.e. no voltage is monitored the circuit has random segment flashing + random flashing of the minus sign.This occurs in (average) same periods like 10sec pause then flashes,10sec pause and again.
Any idea what can the problem be ?
Parts that form the "logical" unit for measuring should be OK,except the R1 which is 180k as written in project page.No C6 and C7 are added.
The power voltages are not perfectly equal - like +5,03V and -5,04V with common ground.The power supply is not a synchronized  dual supply,it has two separate different voltages -the negative and the possitive.

2.When no voltage is monitored what should be written on display ?

3.If this voltmeter is build as an ampermeter can it be used to monitor the current usage of the same curcuit ? The output voltage is stable 5V. ( if i find the attach function will attach an image ).

4.Can this project be done with common cathode instead of common anode ? Or i should use some kind of inverting system for the display ?


I read the topic and found some usefull information about this project.Unfortunately the older links are not working and cant check the whole info aboit it.

The circuit is built in a pcb with many wholes on it (dont know the english name for it )- not the specific pcb on the page.
Using this project : http://www.electronics-lab.com/projects/test/014/index.html
the 7107 is intersil's  ICL7107CPL.The 7-segment displays are some kingbright's and the are different from the displays used in project's page,but schematics is done with modifications in display part to fit the 7seven segments.


And the main question of all :

5. Can someone confirm that the project is working with the circuit posted on the page withoud having to change anything on it (i.e. C6&C7,power supply,etc).
I am asking,because i could done the pcb wrong and have some problems because of that,but the problem (random display flashing) is confusing me - either i messed with the circuit or the 7107 is out of use...
There is no problem to make the same PCB as shown on site (and this topic too),but i need to be some kinda sure,that this project will work as voltmeter.The curcuit i've made so far is for testing only,i hoped it can work properly and then make a "good" PCB for use,but i have problems.

Thanks for reading my reply and i hope someone can help me about the problems i have.

[MP]

Some corrections were posted and then I think I merged all the topics together. They should all be in this thread. That is most likely why some of the old links do not work. Have you read all of the previous posts? I have previously posted a schematic and board layout in eagle format. Others have made this work and have posted about the problems they encountered. I have not heard of the problem with a flashing display. The two missing capacitors are bypass caps for stability of the power supplies. You should add them. Dependent upon how much ripple you have in the power supply, adding the caps might correct the flashing problem.

MP

[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 :)

[MP]

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 ?

[MP]

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 :)

[MP]

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

[audioguru]

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.

[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 ?

[audioguru]

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.

[MP]

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,

[MP]

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 :p, 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!!!!!

[MP]

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

[ante]

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.

[MP]

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?

[kaneco]

i have a power supply for my lab, and i use the lm337 and lm317 and i have the 2n3055 in parallel for more current.

my question is this icl7107 measuring the negative/possitive to -37 0 +37 voltage and the currents at 5A


tank you