Post by thread:[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

"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 removed}

Dear Mr. Richard Seriani, I thank you for your help. The display is working. I added an external voltage divider circuit. Thank you very much. Sairam Message: 25 Date: Wed, 2 Dec 2009 08:00:23 -0500 From: "Richard Seriani" <spam_OUTrseriani48TakeThisOuTcox.net> Subject: Re: [EE] Problem with PM129B 31/2 Digital Panel meter To: "Microcontroller discussion list - Public." <.....piclistKILLspam@spam@mit.edu> Message-ID: <12FD431D95204F9CA91D6AE8B57633A7@RICHARD> Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original "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 removed}

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. Is there any suggestion you may have? Can I try adding a filter to the input? I cannot offer my customer a display which is unreliable. Your help is highly appreciated. Thanks in advance. Regards, Sairam >Message: 43 >Date: Fri, 4 Dec 2009 09:54:16 -0500 >From: "Richard Seriani" <rseriani48KILLspamcox.net> >Subject: Re: [EE] Problem with PM129B 31/2 Digital Panel meter >To: "Microcontroller discussion list - Public." <.....piclistKILLspam.....mit.edu> >Message-ID: <3E3DEACB241E4D96A53BD819D9DBE84F@RICHARD> >Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original {Quote hidden}>Sairam, >Congratulations! >It is always a good feeling when we finally make something work the way we >want it to. >Keep learning. >Richard >Perpetual Student {Original Message removed}

On Fri, Dec 4, 2009 at 10:08 PM, Research Faraday <EraseMEresearchspam_OUTTakeThisOuTfaradayozone.com> 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 markragesspam_OUTmidwesttelecine.com

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

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 <@spam@markragesKILLspamgmail.com> Subject: Re: [EE] Problem with PM129B 31/2 Digital Panel meter To: "Microcontroller discussion list - Public." <KILLspampiclistKILLspammit.edu> Message-ID: <RemoveME74ee72ca0912042022u2ef2eff5x72a26bbbc6c3d5f7TakeThisOuTmail.gmail.com>> Content-Type: text/plain; charset=ISO-8859-1 On Fri, Dec 4, 2009 at 10:08 PM, Research Faraday <spamBeGoneresearchspamBeGonefaradayozone.com> 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 {Quote hidden}> 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 TakeThisOuTmarkragesEraseMEspam_OUTmidwesttelecine.com ------------------------------ Message: 21 Date: Fri, 04 Dec 2009 20:37:54 -0800 From: Bob Blick <RemoveMEbobblickTakeThisOuTftml.net> Subject: Re: [EE] Problem with PM129B 31/2 Digital Panel meter To: "Microcontroller discussion list - Public." <piclistEraseME.....mit.edu> Message-ID: <EraseME4B19E3A2.8070008ftml.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