Question about a circuit again

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1moldmaker
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Question about a circuit again

Post by 1moldmaker » Sat May 02, 2020 4:41 pm

Has any body ever tried to make any of the circuits in the op amp cook book part 4
https://www.nutsvolts.com/magazine/arti ... ook-part-4
basically what I am trying to figure out is what resistors and capicatiors would I need to use for only 20 volt AC
also would I need a voltage divider resistor for an ICL7107 for 20 volts (1.2K)?
Thanks
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dyarker
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Location: Izmir, Turkiye; from Rochester, NY
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Re: Question about a circuit again

Post by dyarker » Sun May 03, 2020 12:39 am

As far as I can tell the parts to the left of the ADC are the voltage divider. (and I don't see the 1.2K you mention in the posted diagram, nor figure 7 in the linked page.)

C2 and C3 may be replaced with a single 30pF. Series caps are -
Ctotal = 1 / ((1/C2) + (1/C3))
(30pF is not a standard value)

R1 and R2 with a 9.9MOhm. Series resistors are -
Rtotal = R1 + R2 (note - 900K = 0.9M)

R3, R4 and R5 with a 10K.

note on C1 - 10nF may be listed as 0.01uF, 10000pF or 10000uuF.
--------------------------------------------
Or, get resistors and capacitors as shown, leave out the switch, wire ADC to where the 20V position of the switch used to be.

Cheers,
Dale Y

1moldmaker
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Re: Question about a circuit again

Post by 1moldmaker » Sun May 03, 2020 5:56 am

Thanks the 1.2k voltage divider that I was talking about I was using on a DC circuit

dyarker
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Re: Question about a circuit again

Post by dyarker » Sun May 03, 2020 6:41 am

A voltage divider needs at least 2 resistors. Input at top lead of upper resistor and bottom lead of lower resistor. Output to measuring circuit is junction of the 2, and bottom lead of lower resistor.

If you are only going to AC with this circuit, then you won't need the DC divider.
Dale Y

1moldmaker
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Re: Question about a circuit again

Post by 1moldmaker » Sun May 03, 2020 8:17 am

Thanks

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