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Led display Digital Voltmeter question


bonanz
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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
 

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  • 5 weeks later...

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  :)

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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
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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
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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!

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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

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  • 1 month later...
  • 4 weeks later...

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.

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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

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Sure. I just get tired of the scare tactics to newbies....you will fry this if you don't follow my instruction....etc.. but then I get emails from those who have built the originals with no problems, grumbling about what they feel is a false posting on this forum.

Projects Q/A is primarily for those who are actively building these projects. Not for theory statements or overall attempt at re-design in one's head. We have a forum for Theory discussions.
Thanks for your input.

MP

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Okay this is not a theory discusssion , i have built the ICL7107 voltmeter and is working great , form www.electronics-diy.com , here is the PCB layout and silkscreen. the lines are jumpers

These are the componenets list

VALUE        SHAPE        #    REFDES     

1.0MOhm_5%  R0204R7_5    1    R6         
1N4148      DIO_DO35    3    D1,D2,D3   
10K_LIN      TRIPOT10X5V  1    R2         
10kOhm_5%    R0204R7_5    1    R5         
10nF        MKHCON4A    1    C7         
10uF-POL    ELKO10R5    2    C1,C2       
15kOhm_5%    R0204R7_5    1    R3         
47kOhm_5%    R0204R7_5    1    R4         
100kOhm_5%  R0204R7_5    1    R1         
100nF        MKHCON4A    1    C4         
100pF        KERKO5X4R5  1    C3         
220nF        MKHCON4A    1    C6         
470nF        MKHCON4A    1    C5         
DIPSW4      DIPSW4H      1    JSW1       
ICL7107      DIP40S      1    U1         
ICL7660      DIP8        1    U2         
JUMPER      JUMPER      20  J1,J2,J3,J4,J5,J6,J7,J8,J9,J10,J11,J12,J13,J14,J15,J16,J17,J18,J19,J20
SEVEN_SEG_DECIMAL_COM_A 7SEG8DIP14B  4    U3,U4,U5,U6 
TEST_PT1    PB          4    GND,INneg,INpos,VCC

ICL7107.rar

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Hello

Someone was asking about the board that someone drewup in eagle. i looked at it and almost made it, went so far as to burn the board. I think that it isn't right. looks like the 7 segments are backwards.
Don't know has anybody eles tried it.  I'll post the files so you can look at em.
                                          gogo

ICL7107.zip

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Hello MP
    I know its a double sided board, what I think I did is burned it upside down.
  I think. I am doing heat transfers so I burned the printed the bottom and mirror the top and then printed. Don't know maybe I should of mirrored the bottom and not the top.  guess I will have to stare at it for awhile

                                          gogo

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hahaha
      Ya MP thats what I think my problem was to begin with.
    Heres what I come up with. I mirrored the bottom layer and just printed the top.
  seems that works. I printed it out and played with it. Makes since that way.
      time to burn another board.
                      have fun gogo

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AH BOO WHO :'(
    that way won't work either, makes the L7660 backards. I would use  the original project but Iwant to put a L7660 right board too.
              Oh well back to the drawing board.

Hey MP someware on this said there was a schmatic posted on the eagle web site, I coulde find it. You wouldn't  happen to have a copy of it  ::)
                            have fun gogo

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Hello
                  MP the eagel pcb you posted don't work unless you drill holes throuth the 7107 to get the 7 segments to place right.    Thanks anyway
                                  back the the org.
                                      have fun gogo

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