Led display Digital Voltmeter question

[MP1]

The project in your link is not measuring the same voltage which is supplying the unit. It is measuring a simple transistor used as a temp sensor. The earlier post about measuring the voltage that you are using for a supply was a reply to a member who wanted to actually measure a varying supply voltage to the voltmeter with the same meter. Problem with this is that your supply voltage to the chip is always changing. Thus, your reference voltage is also always changing. If you continually change your references, you no longer have accuracy.

MP

 

[Oneeye_IO]

I made updated circuit yesterday and it works . Now I have one little problem. Why the shown voltage is 50* larger than input voltage ? I can reduce it with 1K trimmer but it still shows 40* larger value of voltage at trimmer minimum.

 

[MP1]

Can you post your modified circuit?

MP

 

[anderson.salzano]

if I  use a rectifier to read a/c it goes to present an increase of 40 percent of the reading because of the rectification how can I  correct this ???
for example:220V/ac  goes to 308V/dc

Sorry for the inglish! ;D 

 

[MP1]

For such a high voltage, I would recommend to use a step down transformer and then a rectifier. You can then adjust the error in the reference or use an op-amp on the input to offset the error.

MP

 

[faizanbrohi]

HEllo everyone , i would jus like to confirm that if the Eagle Version of the voltmeter    is correct to build , because i need acurracy. i am trying to build a digital voltmeter so i can attach it to a LM2907 Frequency  to Voltmeter Converter , and measure frequencies on the range of 1hZ till 10Khz . although i can also use low pass , band pass and high pass filters for frequency to voltage conversions, then again does the meter has milivolt range and is it that accurate... if this project is complete a higher VHF Filter can be used to measure VHF Frequencies

 

[MP1]

You should check the data sheet to see if the chip has the accuracy you need. This is a simple matter of research and you should do this yourself.

MP

 

[Wiggle]

Hi everyone,

I'm building this Voltmeter together with the supply 30V-3A from the projects.
Now I have some questions about it:

1) How can I supply the voltmeter if i'm using a transfo with only one secundary from    the dc supply? If I put a voltage regulator 7905 behind it, can I messure the output voltage correctly then?

2) If I use the schematic out of the datasheet from the icl7107 i can' t get the correct voltage on my display. I can regulate it to 0 at 0V but I can not get the correct output from a input voltage.

I hope someone can help me out with this,

Greetings Wiggle
 

 

[cynicmonster]

Hi All,

Just looking for some confirmation on a couple of things:

1. I'm looking at running this meter from a wall pack - I assume I still have to regulate the power (i.e. can't just stick a zener in there) as the wall pack may not be regulated;

2. Do I need to do anything to regulate current - that is, if the wall pack is rated 9v 500ma, will the regulator take care of the current?

3. The meter will only be reading +ve voltage, but if I'm going to the trouble of putting it together, I might as well put the -ve supply in as well (protection from wrong connection)...

4. If putting in the -ve supply, should I look at using a 12v wall plug?

Thanks,

Monster 

 

[MP1]

Hi everyone,

I'm building this Voltmeter together with the supply 30V-3A from the projects.
Now I have some questions about it:

1) How can I supply the voltmeter if i'm using a transfo with only one secundary from the dc supply? If I put a voltage regulator 7905 behind it, can I messure the output voltage correctly then?

2) If I use the schematic out of the datasheet from the icl7107 i can' t get the correct voltage on my display. I can regulate it to 0 at 0V but I can not get the correct output from a input voltage.

I hope someone can help me out with this,

Greetings Wiggle

Could you please post a drawing or explain a little more?

MP

 

[MP1]

Hi All,

Just looking for some confirmation on a couple of things:

1. I'm looking at running this meter from a wall pack - I assume I still have to regulate the power (i.e. can't just stick a zener in there) as the wall pack may not be regulated;

2. Do I need to do anything to regulate current - that is, if the wall pack is rated 9v 500ma, will the regulator take care of the current?

3. The meter will only be reading +ve voltage, but if I'm going to the trouble of putting it together, I might as well put the -ve supply in as well (protection from wrong connection)...

4. If putting in the -ve supply, should I look at using a 12v wall plug?

Thanks,

Monster

You should not have the problem of current limitation needed, but others who have built this circuit have complained about the display numbers being a little unstable without real good regulation on the power supply. I recommmend bypass caps at the very least.

MP

 

[cynicmonster]

Thanks MP,

I figure I'm on the right track then.

 

[pacermike]

Hi guys,

I read through all 17 pages of this thread and almost found what I was looking for. A guy asked how you could convert this voltmeter to read millivolts instead of volts but I think the question got lost in the fray because an answer never came up. I read about shunting for reading higher values but it sounds like this won't work backwards for reading smaller values, am I right?

If that's the case then what would I need to do to get a reading in millivolts instead of volts?

p.s. I'm the newest kind of newbie so thanks for any help!

 

[Tristable]

Everybody, Hello!

I'm building power supply from this great community. (looks familiar?)
And yeah, I want to add this meters in my PS.

So, I have 2 questions:
1. As I need only measuring positive voltages, I will use just positive 5V supply.
    And as my meter will be set on 0-200V range (with 0.1 V precision), and as I do
    not need negative sign, can I just remove one 7-seg. display - it would be off
    anyway? Of course, brightness resistor would be bigger.
2. Is original PCB layout OK? I hope that one who made Eagle layout is not angry,
    I appriciate his effort, but I realy dont like boards with askew components.  :
    Well, maybe I remove negative voltage generator and make this resistors
    straight.

Thanks, Triple

 

[kentlee]

Hello!! Everybody.
I am a new member and I want to use this circuit to measure AC voltage around 300V to 400VAC.
Can some one let me know which rectifier circuit can be used??
Thanks a lot!!!

 

[faizanbrohi]

Hello Can i use the Eagle Version of this voltmeter is it ok to build

 

[cynicmonster]

Hi Moderators,

Well, there has ben a lot of inquiry about this voltmeter.

I am truly a Newbie in this field, but can someone PLEASE fix this project so it is an easy project/downoad.

Coupled with the power supply project (30v 2a). it is pretty obvious that ppl want this want this project to complete their unit.

Can someone please supply an updated schem with voltmeter in order to finalise this project. I too have got the eagle version and am waiting confirmation that all is correct.

 

[MP1]

There is no guarantee on any schematic you find on the Internet. That is why there is a discussion area for Q/A of the projects in our project section. Most projects which have a substantial conversation thread will also have a link from the project page. The Eagle version is ok. Also, I am pretty sure corrections in the original project were already made my mixos. This should be clear if you read through the pages of this thread. I uploaded the Eagle version so that members who wanted to make a board had an easier method to do so. As far as your comments about the power supply project, many members have built the original and have had no ill effects. The member who has posted the changes in that forum has not built the device, so I will have to take the word of those who have built it over one who claims to be a theory expert.


MP

 

[cynicmonster]

Thanks MP,

Subtle, but the confidence is there to continue with the project.

Thanks again 

 

[indulis]

From a purely analytical standpoint, "the theory expert" does make SOME valid points!! From a practical, "I only have to build one of these, not 10,000...", it probably doesn't matter!!