Dear Mr.Mark Rages and Mr.Bob Blick, I thank you for your kind help. I added a 4.7uF capacitor in parallel to the 100K resistor. The display value has been stabilised. Thank you very much. I am also thanfkul to Mr. Richard for helping me in this regard. I have just begun my career and all these issues seem to be very new to me. I am able to learn a lot from this forum. Thank you very much. Regards, Sairam >Message: 20 >Date: Fri, 4 Dec 2009 22:22:22 -0600 >From: Mark Rages Subject: Re: [EE] Problem with PM129B 31/2 Digital Panel meter To: "Microcontroller discussion list - Public." Message-ID: <74ee72ca0912042022u2ef2eff5x72a26bbbc6c3d5f7@mail.gmail.com> Content-Type: text/plain; charset=ISO-8859-1 On Fri, Dec 4, 2009 at 10:08 PM, Research Faraday wrote: > I have another issue now. When I connected the 0-20V of a DC RPS, my output > was stable and the values didn't change frequently. Now, I connected the > output of the sensor to the display. When there is no output voltage, the > value of the display keeps changing frequently. i.e 0.01, -0.01, 0.3 etc and > this seems to be highly fluctuating. I am told that the quality of the > components used in the meter is low. > > I checked the same output from the sensor using a multimeter. The value > seems to be relatively stable. When the sensor is idle, the output voltage > is 0.16V and when the output is maximum, the output is 5.01 V. > > I read the ICL7107 datasheet and I came to know that the ADC reacts to the > reverse current from the LEDs and grounding the digital and the analog > signals is necessary. I am going to try grounding the display's ground and > my sensors ground to the body of the enclosure. > The grounding is probably a good idea. It would be nice to look at the signal with an oscilloscope to see what kind of noise is there. I recall you have a voltage divider made of 100k ohm and 9.9M ohm resistors. Try adding a 10 uF capacitor in parallel with the 100k ohm resistor. This will give a low pass filter with a one-second time constant. Regards, Mark markrages@gmail -- Mark Rages, Engineer Midwest Telecine LLC markrages@midwesttelecine.com ------------------------------ Message: 21 Date: Fri, 04 Dec 2009 20:37:54 -0800 From: Bob Blick Subject: Re: [EE] Problem with PM129B 31/2 Digital Panel meter To: "Microcontroller discussion list - Public." Message-ID: <4B19E3A2.8070008@ftml.net> Content-Type: text/plain; charset=us-ascii Research Faraday wrote: > > I read the ICL7107 datasheet and I came to know that the ADC reacts to the > reverse current from the LEDs and grounding the digital and the analog > signals is necessary. I am going to try grounding the display's ground and > my sensors ground to the body of the enclosure. > I don't know if you mentioned where the power for the ICL7107 was coming from. The power supply of the ICL7107 must be totally isolated and floating from that used by the input signal, or else you need to add a differential amplifier to the input of the ICL7107. The ICL7107 is intended for a handheld multimeter with its own 9V battery, so they did not make it easy to share grounds. Cheerful regards, Bob -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist