Can I Replace 10uF Disc Ceramic Capacitor C4 With Electrolytic in PICMeter Part2?

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#1 21680728 22 Sep 2018 20:42

Ken Bush Ken Bush

Anonymous

Post #1
21680728 22 Sep 2018 20:42

I am having some problems obtaining a single 10uF disc ceramic capacitor, shown as C4 on Fig.8, at a reasonable price. Is it detrimental to replace it with an ordinary electrolytic capacitor? Resistors R1 1Mohm and R2 10kohm, shown on Fig.8 appear to have had their idents accidentally reversed on Fig.4 but I think that is obvious from the writeup. The project so far shows great promise and I look forward to its development.Thanks Mike (in the plural).Regards Ken.
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#2 21680729 22 Sep 2018 21:23

PeterTraneus Anderson PeterTraneus Anderson

Anonymous

Post #2
21680729 22 Sep 2018 21:23

I do not have access to the article or to the schematic. If C4 is a power-supply filter capacitor, an electrolytic would probably work. If C4 is in a signal path or precision timing circuit, try using a 10uF film capacitor. A 10 uF film capacitor has more stable capacitance than a 10 uF ceramic capacitor usually has.
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#3 21680730 23 Sep 2018 01:02

Ken Bush Ken Bush

Anonymous

Post #3
21680730 23 Sep 2018 01:02

Thanks for your advise, C4 is in a signal path so it looks as if I will have to bite the bullet and buy one.Cheers.
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#4 21680731 23 Sep 2018 06:03

PeterTraneus Anderson PeterTraneus Anderson

Anonymous

Post #4
21680731 23 Sep 2018 06:03

High-capacitance ceramic capacitors are notorious for their capacitance changing with temperature and with applied voltage. Look up the datasheet for the 10uF ceramic capacitor to see the size of these effects. Film capacitors do not show these effects. Think about what happens if C4 drops in value as the voltage across C4 increases.
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#5 21680732 23 Sep 2018 17:53

Ian Stedman Ian Stedman

Anonymous

Post #5
21680732 23 Sep 2018 17:53

In the circuit, C4 is a low ESR capacitor for the built-in 3.3V regulator. Confusingly the schematic does not show the power supply connections but working with DSPIC devices in the past, I know RA6/VCAP needs a 10uF Tantalum capacitor to work reliably.
Take a look at section 2.4 of the PIC24FV16MK202 datasheet, http://ww1.microchip.com/downloads/en/DeviceDoc/30003030b.pdf for more details.
Ian
#6 21680733 23 Sep 2018 22:14

Ken Bush Ken Bush

Anonymous

Post #6
21680733 23 Sep 2018 22:14

Hi Peter and Ian. Thanks for the advice, I now have some 10 uF Tantalum caps on order. At least I will now have a reasonable chance of a working circuit.Ken
#7 21680734 11 Oct 2018 20:40

Ken Bush Ken Bush

Anonymous

Post #7
21680734 11 Oct 2018 20:40

On page 50 the author says he has forgotten to connect AVDD
(pin 28) and AVSS (pin 27) but on Fig. 8, pin 28 is connected +3v and pin 27 to ground, presumably he means to
their respective pins and not to each other? So far I have the display up and
running and it looks pretty good though a little small for octogenarian eyesight.
Unfortunately I get no response from a voltage applied to the input so its back
to the drawing board!
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Topic summary

The discussion addresses the feasibility of replacing a 10uF disc ceramic capacitor (C4) in the PICMeter Part2 circuit with an electrolytic capacitor due to availability and cost issues. It is clarified that if C4 is part of a power supply filter, an electrolytic capacitor might suffice; however, since C4 is in a signal path or involved in precision timing, a ceramic capacitor's capacitance instability with temperature and voltage makes electrolytic capacitors unsuitable. A 10uF film capacitor is recommended for better stability. Further, C4 serves as a low ESR capacitor for the built-in 3.3V regulator, and a 10uF Tantalum capacitor is advised for reliable operation, referencing the PIC24FV16MK202 datasheet. The user decides to order 10uF Tantalum capacitors to improve circuit reliability. Additional notes mention schematic pin connections for AVDD and AVSS and initial successful display operation, though input voltage response issues remain.
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Can I Replace 10uF Disc Ceramic Capacitor C4 With Electrolytic in PICMeter Part2?

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