"There is a variable resistor "105" available in the back side of the
display. I assumed it was meant for calibration of the display voltage and I
tried adjusting it."
"Is there a possibility that the calibration is wrong. I noticed an
information in the website saying that if needed, we must add proper voltage
dividers and decimal point wire jumper. I don't have an idea what they meant
by this information."

The second link you provided contains this information. No need to "assume".
The fact that this is a 200mV full-scale display means that, if you want to 
measure voltages higer than that, you need a voltage divider. The chart in 
the datasheet is pretty clear on the values you need. For 20V full-scale, 
use an input voltage divider made up of a 100K resistor and a 9.9M resistor. 
Look at the relationship between those values and the relationship between 
the 200mV and 20V full-scale you are trying to achieve.

You may want to do a search on DC voltmeters so you can see how input 
voltage selection is usually accomplished. That may help.

Good luck.

Richard





----- Original Message ----- 
From: "Research Faraday" <research@faradayozone.com>
To: <piclist@mit.edu>
Sent: Wednesday, December 02, 2009 12:40 AM
Subject: [EE] Problem with PM129B 31/2 Digital Panel meter


> Dear All,
>           I am trying to display my sensor's output voltage to the PM129B
> 31/2 Digit LED Digital Panel Meter.
>
> The display information is available at the following link:
>
> http://store.kysanelectronics.com/servlet/-strse-68458/PM129B/Detail
>
> The data sheet of the display is available at this link:
>
> http://www.circuitspecialists.com/images/PM-129A&Bspecs.pdf
>
> The display uses a ICL7107 IC which has A/D conversion and display
> utilities.
> http://www.intersil.com/data/fn/fn3082.pdf
>
> The problem I am facing is that I am not able to read the output voltage
> using the display. The voltage uses a 5V power supply. I have set the
> display's voltage range to be 0-20V.
>
> When I switch on the power supply to the display, it shows that "0.00". 
> So,
> I concluded that the display is in good condition.
>
> Now, when I tried giving a 12V to the analog input pins, to test the
> display, it is displaying the character 1 and a dot. When I cut off the
> signal voltage, I see that the value indicated is gradually reducing to
> zero. I also noticed that it seems to decrease from some random higher
> value. For example, while decreasing, it shows values like this 16.36, 
> 12.00
> and so on until it shows zero.
>
> There is a variable resistor "105" available in the back side of the
> display. I assumed it was meant for calibration of the display voltage and 
> I
> tried adjusting it. There were no changes and it was showing the same
> character 1 when I provided the input voltage. In order to double check
> this, I tried giving a signal using a 1.5V battery. It seems to show the
> same character 1.
>
> Is there a possibility that the calibration is wrong. I noticed an
> information in the website saying that if needed, we must add proper 
> voltage
> dividers and decimal point wire jumper. I don't have an idea what they 
> meant
> by this information.
>
> Any help in this regard, would be appreciated.
>
> Thanks in advance.
>
> Regards,
> Sairam
> -- 
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist 

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