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Led display Digital Voltmeter question

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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

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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?

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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

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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

post-10630-14279142315553_thumb.jpg

post-10630-1427914231611_thumb.jpg

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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

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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

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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

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I haven't found that to be true. I have samples from both manufacturers and in my bench tests have found both to be stable. In most cases where someone has complained, I have found it to be a board layout error or design error. Most problems are cured by reading the application notes and data sheets.

MP

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I'm using the ICL7107CPL from Intersil. Incidently, I bought a Texas Instruments version today and plugged it in and the same thing happened. I think what will be best is if I scrap my old circuit and build another one from scratch. I find that sometimes helps to get kinks out that I miss. I'm still willing to hear any advice on the subject!

--Amr

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MP,
Intersil also have an improved one, also with guaranteed stability like Maxim's. Which one did you try and are people complaining about Intersil's old original one?

Actually, it was your comments in the past about the specs that caused me to get the Maxim sample and compare. I have always used the Intersil chip in the past since as a general rule Maxim is always more expensive. Unfortunately, I have not noticed any differences. The two ICs that I compared were Intersil from approximately 2 years ago and Maxim from a more recent sample.
Reference voltage and supply voltage are critical in any A/D converter. Problems in those two general areas are the most common cause of instability in LED or LCD readings when using an A/D converter of any kind.

MP

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Good news! I've just rebuilt the circuit using the Texas Instruments chip and breadboard and it works perfect! What's more, I replaced the TI chip for the Intersil one and it works just as well! I must have made some mistake in my PCB the first time. Anyway, I'm glad that's all sussed.

Thanks for all the comments and help everyone!

--Amr

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Dear Jose,
Your post did not translate very good. Are you asking if this Integrated Circuit Chip, ICL7107SCPLZ is a direct replacement for the 7107 in the project on this wesite?

MP

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

7107cv.gif

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:

ammeter 7107.GIF


What if I wanted to measure resistance? Could this DVM be modified, if so how?

Thanks

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Hi, After reading all the experts building their own voltmeter. (using the ICL7107)
I decide to make a try and follow all the intruction...BINGO ...It's works with accuracy ...BUT one problem, I can't adjust adjust to Zero setting (without any load), always read as minus 00.1/00.2 If I tune to zero the reading with load will not accurate.

Anybody know the faults of have the answer?

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Hello MP

The different is about 5 to 5.5v short with tunning to zero, the last digit still flicking between one and zero, if witout flicking (zero is stable) is about 6v less

although I'm able to set zero, the minus sign is always appeared, but when loaded with current to read the voltage, the minus will go off,...any answer?

Dan

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Hi MP,
thanks for the attachment

I manage to solved the negative sign by grounding the pin 30 (also can be connected to pin 21). the minus sign goes off.

But still can't rectify the zero setting problem, anyway the VM works find and accurate when put on load,

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