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bonanz

Led display Digital Voltmeter question

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I tried to build the L.D.D.V. yesterday, using a breadboard and
I came up with peculiar readings on the LEDs. ??? I had followed the
schematic from smartkit.

I thought that I had a false ICL7107 and I dismounted the
components. :-[

Today I thought to check the data sheets of ICL7107 and MAN6960 in order to cross-check the connections. Found [glow=red,2,300]inconsistencies[/glow] in the
article schematic ! >:(

For example for the 1's display :

Article : ICL(6) -> MAN(10)
Should be : ICL(6) -> MAN(9)

another example :

Article : ICL(34)
Should be ICL(25) -> MAN(1) and so on... there are many there.

Moreover, the R1 should be 100K, not 180K, I refer to the datasheet
and the "Digital Voltmeter" project

Finally, the LCD dot, is pin number 5, emitted in the schematic.

I am about to search all the errors now and report back later,
after I will rebuild the voltmeter.

I attach the data sheets for further reference. 8)



Hi Billy,

After comparing the schematic with ICL7107 datasheet, I also realized those problems which are already mentioned by you.

If you have rectified those errors, and have drawn proper schematic, please put it on or mail it to me. I want to use it in my lab PSU.

Regards,

Ani

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blacksheep: you can use this Voltemeter as ammeter also using the connections see below:



You connect the ammeter in series with the load and voltmeter in parallel with load. To take a current measure there must be a load connected :D

Also you can read this: http://www.electronics-lab.com/forum/attachments/Digital_Panel_Meter.pdf
explaining different connections and R calculations.

Or use this to measure current:

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Here is a schematic and board layout that was donated by someone to the Eagle site. It is free to use. It looks like the project, but might be a little different. If you have the free version of the eagle, you can view it or even edit it to be what you want. If you do not have the free version of Eagle, go to http://www.cadsoftusa.com/ and download it.

ICL7107.zip

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mixos: Thank you very much for your reply... i have one more question: I've made a digital amperemeter with a voltage-to-frequency-converter (LM131), an amv (NE555), some mmv's (MC14538), some bcd-counters (MC14518) and some bcd-to-7segment's (MC14511).... is it possible to build an ampere meter in the same way, or do i need a "ampere-to-frequency-converter"? ;) sounds a little funny...

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First of all I attach here the FIXED SCHEMATIC (22-2-04):





I attach also two sample power supplies for this voltmeter:





Hope this one solves all previously mentioned inconsistencies. Also the schematic at the project's page is updated:

http://www.electronics-lab.com/projects/test/014/

blacksheep : To measure the current flows a load you use a small resistor in series with the load and you measure the voltage drop on it. Then with ohm's law you calculate the current pass throught the resistor and throught your load. You can't easily measure the current right away. So you can use the same circuit to measure the voltage drop across a resistor. For more info on how to do this see the pdf file i indicated previously.

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Here is a schematic and board layout that was donated by someone to the Eagle site. It is free to use. It looks like the project, but might be a little different. If you have the free version of the eagle, you can view it or even edit it to be what you want. If you do not have the free version of Eagle, go to http://www.cadsoftusa.com/ and download it.


These are the contents of the zip file for fast view of another 7107 digital voltmeter (it's almost the same, but this one incudes the +/-5V power sources)








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This is about the power source using the 1K resistors, I used the LM 317T for positive voltage because I found out the 7805 refused to work with the 7905, this I have tested over and over again beforew comin to that conclusion. A positive voltage enters the 317T and is varied until +5V is at its output.

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Guest Kasamiko

Hi all,
Where can I get the "EXACT" PCB pattern layout for this project? I tried to used the layout in this post but everytime I print it out it's always oversized.. :(
I set my printer to 1:1 but to no avail..
please help.. :'(

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The best way to print it out correctly is to make some test prints to find the correct ratio. Take a part with fixed dimensions and try to fit on the print out paper. Then change accordingly the ratio to achieve the correct dimensions. It is better to use a program that allow you to change the percentage (%) of the print out and not the ratio.

I don't know another more "easy" way to print a PCB from an image file.

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Kasamiko, if that will not work for you, here are the eagle board and schematic files. If you do not have the free eagle layout editor, you can get it from the dowmload links on this site. You can edit these files with this version of Eagle to make the design more specific of your application.

MP

ICL7107_Files.zip

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If you download the Eagle layout files, you can move the parts on the board. Breadboards, Veroboards, etc. are boards with multiple holes on a 0.1" pattern. You could edit the board layout by removing the traces, then moving all the parts so that they match the 0.1" pattern. ..or you can delete the board layout and automatically generate a new board layout from the schematic, then place all the parts where you want them. After that, using the autorouter will put the line where you can see them and know where to put your wires on the breadboard.

MP

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Stu,

Continuing from message: I have drawn a circuit for you that show the basic connection for your equipment with the meter hocked on. With the switch you choose current or voltage reading. Current is measured over the shunt (resistor voltage drop) and the voltage across the terminals pos and neg.

Ante ::)

post-929-14279141621536_thumb.gif

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Hi,

I built this voltmeter circuit, but have a question regarding the power supply for it. I notice the schematics show ground symbols in addition to + and - supply voltage. So would these indicate true earth grounds? I ask because I want to be able to use a digital voltmeter like this in my car, where (I believe) there would be no true ground?

Is there any way to get around this? I was able to get the 7805 to produce 5.0 volts when it's ground leg is attached to the - terminal of the 12 volt battery i'm using (and its V. in leg attached to the +12 volt battery terminal). I doubt this would work for the 7905 to make a -5volt supply though? ???

Thanks
-Nick

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You will need a negative voltage. A 7905 will only work with a negative input. There is a chip from maxim that will do what you want. It just converts your +5 to -5. Another way to do this is to use an inverter circuit to divide your battery voltage by two and give you a bipolar 6 volt supply. The maxim chip is the best solution.
There are some additional notes earlier in this thread regarding the -5 volt. It is here:
http://www.electronics-lab.com/forum/index.php?board=2;action=display;threadid=119;start=15

There were also some corrections to the circuit posted in earlier messages and also here:
http://www.electronics-lab.com/forum/index.php?board=4;action=display;threadid=353


MP

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Hi all,
Where can I get the "EXACT" PCB pattern layout for this project? I tried to used the layout in this post but everytime I print it out it's always oversized.. :(
I set my printer to 1:1 but to no avail..
please help.. :'(



Try to use a drawing software like photo shop or paint shop pro to resize the pcb and before you print always check the size from print preview so you would know if it's over sized or not!

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