Led display Digital Voltmeter question

[ferio]

Can someone tell me if I can buy the PCB board or do I have to make the PCB board my self?

 

[MP1]

I think there is a smart kit for this project. Search for Smart Kits.

MP

 

[bilalhasani]

hi to everybody here
i am a new comer here with my 1st post, and i am really impressed to see the way you people are working for projects and discussing about them for the benefit of beginners like me.
i saw the LED display voltmeter and also browsed through the discussion about it, and i think its an ideal project for any beginner to start.

but i have some questions about it before its practical implementation (dont laugh if you find them too childish)
First Question:

for multi range, its recommened to use 0 ohm for 0-2 volts, 120 k ohm for 0-20, 12 k ohm for 0-200, and 1.2 k ohm for 0-2000.
i cant understand why no resistance for 2 volt, then suddenly increases 120 k for 20 V, then it gradually decrease for 200 and 200 V. I have always seen resistances increasing or decreasing in any multi range meter (current, voltage etc). but here it is showing different change ????

Second Question:

what about type of capacitors used? in diagram, they seem to be non polar but i want to confirm about their type. also voltage ratings of capacitors is not mentioned???

Third Question:

from the discription of circuit, it is clear that the IC 7107 is very delicate, what does it mean?? will the voltmeter be also very delicate that it may damage for a very small excessive voltage... So please make me clear about the tolerance level about which it can withstand.

thank you very much for reading all this stuff written by me...
waiting for a kind reply
bilal

 

[cdonke]

if the input is 5.6v will it read 5.6 or only 5????

 

[shankar1]

Some people recommend using IC for generating the -5V. But the best thing to do is to have a resistor divider across the -15 V which is available in all the voltage source to produce the -5V.

 

[audioguru2]

Hi Shankar,
A resistor divider would waste a lot of power and wouldn't regulate the -5V very well.
A linear series voltage regulator IC is a voltage divider that hardly wastes anything and regulates the -5V extremely well. ;D

 

[MP1]

I normally use an ICL7660 for a negative supply on mine, but the datasheet for the ICL7106 and 7107 shows how to use a CD4009 and some diodes to generate the negative voltage from the oscillator pins. This is probably the simplest. The negative side does not need much current.

MP

 

[amir kargar]

thats very good
thanks
can i ask where are you live?

 

[ante1]

This is one way to do it:

View attachment 37172

 

[luisrosario]

I every body

I'm new here and i've read all the discussion forum, i'm shure it hellpe me doing my digital votlmeter.
I read that the IC 7107 can read capacitors to. Do any body try to do it??
i'de like to do one. Can any body hellpe me???

Thanks

View attachment 37221

 

[kauvi]

I was so fascinated that I decided to build the voltmeter on the breadbaord. It couldn't work correctly. It was just flshing. C6 and C7 are only on the components list and the PCB where are they on the schematic.

I am dissapointed cause I have probably messed up my ICL7107 IC

 

[MP1]

C6 and C7 are only on the components list and the PCB where are they on the schematic.

I am dissapointed cause I have probably messed up my ICL7107 IC

C6 and C7 are bypass caps for the power supply in case you need to clean it up. Leaving these off the board will not ruin your chip. There must be something else wrong with your layout.

MP

 

[bassemessam]

i have used the design of this circuit for a project was required for me but i faced a problem after making it . the reading of the display doesnot stay on a fixed numbers it changes rapidily and also doesnot give the actual reading . all the connections is right .
HINT: i didnot use the diplay MAN6960 as shown in the explain of the circuit couz i didn't find it in stores but i think that doesn't make a problem couz i used a common anode displays.
please i need a solve for this poblem?

 

[MP1]

You might want to post your schematic and board layout that was used. It has been my experience that when someone makes the same circuit, but only a little different, that means it is a different circuit. If you will post, others might be able to give you some ideas. Normally fluctuating numbers on one of these circuits is due to supply filtering, or I should say the lack of. Did you use bypass caps in the circuit? Another thing to look at is the board layout. Routing can sometimes cause you headaches that are hard to find.

MP

 

[Amr Bekhit]

I have the same problem as bassemessan. The meter readings are extremely unstable. The datasheet does specify that the oscillator capacitor should be ceramic, the integrator should be polypropylene and the reference and auto-zero should be Mylar or polystyrene. I have done so in my circuit and it's still just as unstable as ever. The meter is configured for 2V fullscale. I have fixed a 1M-100k potential divider so that I can input a maximum of 20V. I've attached my circuit diagram and PCb layout. Any help is greatly appreciated.

--Amr

View attachment 37297

View attachment 37298

 

[MP1]

Are you using bypass caps on the +5V and -5V connections? There should be a capacitor from these supply lines to common or 0V. Be careful to make sure you use the correct polarity. Compare the project board and the schematic and you will see that the project uses the bypass caps. You should be able to use something in the area of 10 uf. In many cases even much smaller. Depends upon what you are using to power this circuit.

MP

 

[Amr Bekhit]

The circuit is powered by a regulated and smoothed dc power supply. Is this not good enough?

--Amr

 

[MP1]

Which project did you use? There are two which are similar. There is one from Smart Kits and one from Zeus electronics. If you used the Smart Kit project at:
http://www.electronics-lab.com/projects/test/014/index.html 
Look at C6 and C7 on the board. There is also a description in the text about using bypass caps.
If you used the project from Zeus electronics at:
http://www.electronics-lab.com/projects/test/007/index.html   
it does not show the use of bypass caps. However, I would not skip this important component. There are a lot of ways noise can get into your circuit between a filtered power supply and the final destination. Hope this is helpful.

MP

 

[Amr Bekhit]

I haven't used any kits. I came across the chip in a book and used the datasheet to design my circuit. When the circuit refused to work properly, I searched on the net for a solution and found this site.

I will try the bypass caps and see how it goes.

Thanks form the help so far!

--Amr

 

[audioguru2]

Maxim's improved IC is much more stable than Intersil's original one. ;D